JP2014149258A - Retroreflection device and terahertz wave measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a retroreflection device and a terahertz wave measurement device in which retroreflection can be performed on light even when inclination of retroreflection means such as a retroreflection mirror for performing retroreflection on light occurs.SOLUTION: A retroreflection device 120 includes: first retroreflection means 121; and second retroreflection means 122. The first retroreflection means has directional dependence in which retroreflection is disabled by inclination of the first retroreflection means 121 along a first direction and retroreflection is enabled even when inclination of the first retroreflection means 121 along a second direction occurs. The second retroreflection means 122 has directional dependence in which retroreflection is disabled by inclination of the second retroreflection means 122 along a third direction and retroreflection is enabled even when inclination of the second retroreflection means 122 along a fourth direction occurs. The first and second retroreflection means are arranged such that the second direction and the fourth direction intersect with each other.

Description

  The present invention, for example, includes a retroreflective device that retroreflects light and a terahertz that analyzes the characteristics of an object to be measured using terahertz time domain spectroscopy using light that has been optically delayed by such a retroreflective device. The present invention relates to the technical field of wave measuring devices.

  As a terahertz wave measuring apparatus, an apparatus using terahertz time-domain spectroscopy is known (for example, see Patent Document 1 to Patent Document 3). The terahertz wave measuring apparatus analyzes the characteristics of the measurement object according to the following procedure. First, pump light (in other words, excitation light), which is one laser light obtained by branching ultrashort pulse laser light (for example, femtosecond pulse laser light), generates terahertz waves to which a bias voltage is applied. The element (particularly the gap portion of the photoconductive antenna included in the terahertz wave generating element) is irradiated. As a result, the terahertz wave generating element generates a terahertz wave. The terahertz wave generated by the terahertz wave generating element is irradiated to the measurement object. The terahertz wave irradiated to the measurement object is another laser light obtained by branching the ultrashort pulse laser light as reflected light or transmitted light from the measurement object, and is optically delayed with respect to the pump light. In other words, the terahertz wave detection element (in particular, the gap portion of the photoconductive antenna included in the terahertz wave detection element) irradiated with the probe light (in other words, excitation light) to which the (optical path length difference) is applied is irradiated. As a result, the terahertz wave detecting element detects a current signal corresponding to the intensity of the terahertz wave reflected or transmitted by the measurement object. Thereafter, the detected terahertz wave (that is, a terahertz wave in the time domain and a current signal) is Fourier-transformed to obtain a spectrum of the terahertz wave (that is, frequency response characteristics of amplitude and phase) and the like. The As a result, the characteristics of the measurement object are analyzed by analyzing the spectrum of the terahertz wave.

International Publication No. 2000/079248 Pamphlet JP 2001-21503 A JP 2006-329857 A

  Here, the optical delay imparted to the probe light (or pump light) is a retroreflective device (or such a retroreflective device including a retroreflector capable of retroreflecting incident light). In many cases, the probe light (or pump light) is incident on the optical delay device including the optical delay device. Here, “retroreflection” refers to a state in which incident light is reflected in a direction parallel to the incident direction of the incident light. As an example of the retroreflecting mirror, a retro reflector is exemplified. However, in order to manufacture a retro-reflector, it is necessary to arrange three reflecting mirrors whose reflecting surfaces intersect with each other at an angle of 90 degrees with high accuracy. For this reason, it is difficult to manufacture a retroreflector having high deflection angle accuracy (that is, parallelism of reflected light with respect to incident light).

  For this reason, from the viewpoint of ease of manufacture, a retroreflecting mirror composed of two reflecting mirrors each having an angle of 90 degrees is often used. However, a retroreflector composed of two reflectors is different from a retroreflector composed of three reflectors, and when the retroreflector tilts due to vibration or the like, the retroreflector tilts. Depending on the direction, retroreflection may be impossible. For example, even if two reflecting mirrors are tilted along a direction along the plane including the optical path of incident light and the optical path of reflected light when the retroreflecting mirror is retroreflecting, the retroreflecting mirror is Can continue to reflect. On the other hand, if the two reflecting mirrors are tilted in a direction different from the direction along the plane including the optical path of the incident light and the optical path of the reflected light when the retroreflecting mirror is retroreflecting, The reflector cannot be retroreflected. When retroreflection is impossible, the probe light (or pump light) reflected by the retroreflecting mirror is appropriately applied to the gap portion of the photoconductive antenna of the terahertz wave detecting element (or terahertz wave generating element). There is a risk that it will not be. As a result, the analysis accuracy of the characteristics of the measurement object using terahertz waves may be affected.

  Examples of problems to be solved by the present invention include the above. It is an object of the present invention to provide a retroreflective device and a terahertz wave measuring device capable of retroreflecting light even when a retroreflective means such as a retroreflecting mirror that retroreflects light is tilted. And

  A retroreflective device that solves the above problem is a retroreflective device that retroreflects incident light, and is retroreflected by the first retroreflective means that retroreflects the light and the first retroreflective means. Second retroreflective means for retroreflecting the light toward the first retroreflective means, wherein the first retroreflective means is configured by the inclination of the first retroreflective means along a first direction. While retroreflection becomes impossible, the retroreflection is possible even if the first retroreflection means tilts along a second direction different from the first direction. The second retroreflective means makes the retroreflective impossible by the inclination of the second retroreflective means along the third direction, while the second retroreflective means along the fourth direction different from the third direction. Even if the inclination of the retroreflective means occurs, the recursion Morphism has direction dependency that is possible, the and so intersects the second direction and the fourth direction, wherein the first retroreflector and the second retroreflector is arranged.

  A terahertz wave measuring apparatus that solves the above-described problems is a generation unit that generates a terahertz wave by irradiating a first laser beam, and a measurement object from the generation unit by irradiating a second laser beam. Detecting means for detecting the terahertz wave irradiated to the first laser beam and the second laser beam retroreflecting one of the first laser beam and the second laser beam retroreflected. A retroreflective device that guides at least one of the laser beams to at least one of the generating unit and the detecting unit, wherein the retroreflective device includes the first laser beam and the second laser beam. First retroreflective means for retroreflecting any one of the first retroreflective means, and any one of the first laser light and the second laser light retroreflected by the first retroreflective means, And a second retroreflective unit that retroreflects toward the reflecting unit, and the first retroreflective unit makes the retroreflective impossible by the inclination of the first retroreflective unit along the first direction. On the other hand, the second retroreflective means has the direction dependency that the retroreflective is possible even when the inclination of the first retroreflective means along the second direction different from the first direction occurs. The retroreflective means cannot be retroreflected by the inclination of the second retroreflective means along the third direction, while the second retroreflective means is inclined along a fourth direction different from the third direction. However, the first retroreflective means and the second retroreflective means are arranged so that the second direction and the fourth direction intersect with each other. ing.

It is a block diagram which shows the structure of the terahertz wave measuring device of 1st Example. It is a perspective view which shows each structure of a terahertz wave generation element and a terahertz wave detection element. It is a top view which shows the optical path (incident optical path and reflected optical path) of the probe light with respect to the inclination (position shift | offset | difference) of a movable retroreflection mirror. It is a perspective view which shows the arrangement | positioning aspect of the movable retroreflection mirror and fixed retroreflection mirror in 1st Example. It is a top view which shows the example of the optical path of probe light when a movable retroreflection mirror inclines in the optical delay device of 1st Example. It is a top view which shows the other example of a structure of the optical delay device in 1st Example. It is a top view which shows the optical path (incident optical path and reflected optical path) of the probe light with respect to the inclination (position shift | offset | difference) of a movable retroreflection mirror. It is a block diagram which shows the structure of the terahertz wave measuring device of 2nd Example. It is a perspective view which shows the arrangement | positioning aspect of the movable retroreflection mirror and fixed retroreflection mirror in 3rd Example.

  Hereinafter, embodiments of the retroreflective device and the terahertz wave measuring device will be described in order.

(Embodiment of retroreflective device)
<1>
The retroreflective device of this embodiment is a retroreflective device that retroreflects incident light, and the first retroreflective means retroreflects the light and the retroreflected by the first retroreflective means. At least one of the second retroreflective unit, the second retroreflective unit, and the second retroreflective unit that retroreflects the light so that the light propagates along an optical path that reciprocates between the first retroreflective unit and the first retroreflective unit. Moving means for moving one side in the optical axis direction of the light incident on at least one of the first retroreflective means and the second retroreflective means, and the first retroreflective means includes The inclination of the first retroreflective means along the first direction makes the retroreflecting impossible, while the inclination of the first retroreflective means along the second direction different from the first direction occurs. Can also be retroreflective The second retroreflective means is not retroreflective due to the inclination of the second retroreflective means along the third direction, while the third direction is It has direction dependency that the retroreflection is possible even if the second retroreflective means is inclined along different fourth directions, so that the second direction intersects the fourth direction. The first retroreflective means and the second retroreflective means are disposed.

  According to the retroreflective device of the present embodiment, the light incident on the retroreflective device is retroreflected by, for example, the first retroreflective means. At this time, the first retroreflective unit may reflect the light incident on the first retroreflective unit toward the second retroreflective unit (for example, toward the reflection surface of the second retroreflective unit). preferable. As a result, the second retroreflective means can retroreflect the light retroreflected by the first retroreflective means. At this time, the second retroreflective means may reflect the light incident on the second retroreflective means toward the first retroreflective means (for example, toward the reflection surface of the first retroreflective means). preferable. That is, in this embodiment, the optical path of the light incident on the retroreflective device is an optical path that reciprocates between the first retroreflective means and the second retroreflective means. As a result, the retroreflective device can retroreflect the light incident on the retroreflective device.

  In addition, since at least one of the first retroreflective unit and the second retroreflective unit is movable, the retroreflective device includes an optical path of light incident on the retroreflective device and an optical path of light not incident on the retroreflective device. Can be adjusted as appropriate. In other words, the retroreflective device can set the optical path length difference between the optical path of light incident on the retroreflective device and the optical path of light not incident on the retroreflective device to a desired value. Therefore, the retroreflective device can be substantially used as an optical delay device that can dynamically adjust the amount of optical delay imparted to the light. However, both the first retroreflective means and the second retroreflective means may be fixed. That is, the retroreflective device may not include a moving unit.

  In consideration of the fact that the optical path of the light incident on the retroreflective device is an optical path that reciprocates between the first retroreflective means and the second retroreflective means, the first retroreflective means retroreflects the light. In the state in which the second retroreflective means retroreflects the light and the optical path of the light incident on the first retroreflective means and the optical path of the light reflected by the first retroreflective means in the second state It is preferable that the optical path of the light incident on the retroreflective means and the optical path of the light reflected by the second retroreflective means are aligned (preferably parallel).

  Here, the first retroreflective means has a direction dependency on the inclination of the first retroreflective means. Specifically, the first retroreflective means has a direction dependency that the possibility of retroreflection changes depending on the inclination direction of the first retroreflective means. More specifically, the first retroreflective means has a direction dependency that the retroreflective becomes impossible by the inclination of the first retroreflective means along the first direction. On the other hand, the first retroreflective means has the direction dependency that the retroreflective is possible even if the inclination of the first retroreflective means along the second direction occurs.

  Similarly, the second retroreflective means has a direction dependency on the inclination of the second retroreflective means. Specifically, the second retroreflective means has a direction dependency that the possibility of retroreflection changes depending on the inclination direction of the second retroreflective means. More specifically, the second retroreflective means has a direction dependency that the retroreflective becomes impossible by the inclination of the second retroreflective means along the third direction. On the other hand, the second retroreflective means has a direction dependency that the retroreflective is possible even when the inclination of the second retroreflective means along the fourth direction occurs.

  The first direction and the second direction are preferably orthogonal to each other. However, as long as the first direction and the second direction are different from each other, the first direction and the second direction may be any direction. Similarly, the third direction and the fourth direction are preferably orthogonal to each other. However, as long as the third direction and the fourth direction are different from each other, the third direction and the fourth direction may be any direction.

  In particular, in the present embodiment, the first retroreflective means is used to realize a state in which the retroreflective device can retroreflect light incident on the retroreflective device without depending on the inclination of the first retroreflective means. The second retroreflective means is arranged as follows in consideration of such direction dependency on the retroreflection. Specifically, the second direction enabling retroreflection in the first retroreflective means and the fourth direction enabling retroreflection in the second retroreflective means intersect (preferably orthogonally), First retroreflective means and second retroreflective means are arranged.

  By arranging the first retroreflective means and the second retroreflective means in this manner, the first retroreflective means is inclined along the first direction as will be described in detail later with reference to the drawings. Even in this case, the light itself incident on the retroreflective device is retroreflected by the retroreflective device. In other words, even if the first retroreflective means alone makes retroreflecting impossible, retroreflecting becomes possible when viewed from the entire retroreflective device.

  This is because the optical path is disturbed due to the inclination of the first retroreflective means (that is, the first retroreflective based on the optical path when the light is retroreflected when the first retroreflective means is not inclined). This is because the disturbance of the optical path when the light is retroreflected in a state where the means is inclined is substantially canceled or compensated by the second retroreflective means. More specifically, in the first retroreflective means, a total of two times of reflecting the light toward the second retroreflective means and reflecting again the light retroreflected by the second retroreflective means, Light is incident and reflected. Then, when the light is reflected toward the second retroreflective means, the optical path is disturbed due to the inclination of the first retroreflective means, but when the light retroreflected by the second retroreflective means is reflected again. The disturbance of the optical path is canceled or compensated.

  When the first retroreflective means is inclined along the second direction (that is, when the first retroreflective means alone can be retroreflected), the light incident on the retroreflective device Needless to say, this is retroreflected by the retroreflective device.

  As described above, the retroreflective device of the present embodiment has an inclination of retroreflective means (that is, the first retroreflective means) such as a retroreflector that retroreflects light (in particular, in a direction in which retroreflective is impossible). Even if a tilt occurs, the light can be retroreflected.

<2>
In another aspect of the optical delay device of the present embodiment, the first retroreflective means and the second retroreflective means are arranged so that the second direction and the fourth direction are orthogonal to each other.

  According to this aspect, the retroreflective device can retroreflect light even when the inclination of the first retroreflective means (particularly, the inclination in the direction in which retroreflection is impossible) occurs. .

<3>
In another aspect of the optical delay device of the present embodiment, the first direction includes an optical path of the light incident on the first retroreflective means in a state where the first retroreflective means retroreflects the light, and The direction is different from the direction along the plane including the optical path of the light retroreflected by the first retroreflective means, and the second direction is the first retroreflective means retroreflects the light. A direction along a plane including the optical path of the light incident on the first retroreflective means in a state and the optical path of the light retroreflected by the first retroreflective means, and the third direction is the second direction A direction along a plane including the optical path of the light incident on the second retroreflective means and the optical path of the light retroreflected by the second retroreflective means in a state where the retroreflective means retroreflects the light. Is a different direction, and The four directions are: an optical path of the light incident on the second retroreflective means in a state where the second retroreflective means retroreflects the light and an optical path of the light retroreflected by the second retroreflective means It is the direction along the plane containing.

  According to this aspect, as will be described in detail later with reference to the drawings, the first retroreflective means applies the first retroreflective means to the first retroreflective means in a state where the first retroreflective means is retroreflecting light. The inclination (typically) of the first retroreflective means along a direction (typically intersecting or orthogonal) different from the direction along the plane including the incident optical path of light and the reflected optical path of light from the first retroreflective means Specifically, the direction dependency is that retroreflection becomes impossible due to the direction along the plane and the inclination of the first retroreflective means whose rotation center is the direction orthogonal to the incident optical path and the reflected optical path of light. have. In addition, the first retroreflective unit includes an incident optical path of light to the first retroreflective unit in a state where the first retroreflective unit retroreflects light, and reflection of light from the first retroreflective unit. It can be said that retroreflection is possible even if the inclination of the first retroreflective means along the plane including the optical path (typically, the inclination of the first retroreflective means having the direction orthogonal to the plane as the rotation center) occurs. It has direction dependency.

  Similarly, the second retroreflective means includes an incident light path of light to the second retroreflective means in a state where the second retroreflective means retroreflects light, and the light from the second retroreflective means. The inclination of the second retroreflective means along the direction different from the direction along the plane including the reflected light path (typically intersecting or orthogonal) (typically the direction along the plane, It has a direction dependency that the retroreflection becomes impossible by the inclination of the second retroreflective means having a rotation center in the direction orthogonal to the incident optical path and the reflected optical path. In addition, the second retroreflective means includes an incident optical path of light to the second retroreflective means in a state where the second retroreflective means retroreflects light and reflection of light from the second retroreflective means. It is said that retroreflection is possible even when the inclination of the second retroreflective means along the plane including the optical path (typically, the inclination of the second retroreflective means having the direction orthogonal to the plane as the rotation center) occurs. It has direction dependency.

  According to such an aspect, the retroreflective device retroreflects light even when the inclination of the first retroreflective means (particularly, the inclination in a direction in which retroreflection is impossible) occurs. Can do.

  The state in which the first retroreflective means and the second retroreflective means are arranged so that the second direction and the fourth direction cross each other is substantially (i) the first retroreflective means recurs light. In a state where the optical path of light incident on the first retroreflective means and the optical path of the light reflected by the first retroreflective means in the reflected state and the second retroreflective means retroreflect the light The first retroreflective means and the second retroreflective means so that the optical path of the light incident on the second retroreflective means and the plane including the optical path of the light reflected by the second retroreflective means intersect (preferably orthogonal) It can be said that it is equivalent to the state where is arranged.

<4>
In another aspect of the retroreflective device of the present embodiment, the first retroreflective means has a first reflecting mirror and a second reflecting surface that intersects the reflecting surface of the first reflecting mirror at an angle of 90 degrees. The second retroreflecting means includes a third reflecting mirror and a fourth reflecting mirror having a reflecting surface that intersects the reflecting surface of the third reflecting mirror at an angle of 90 degrees. The first direction is a direction where the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror are opposed to each other, and the second direction is a reflection of the first reflecting mirror. The third direction is a direction in which the reflecting surface of the third reflecting mirror and the reflecting surface of the fourth reflecting mirror are opposed to each other. The fourth direction is a direction in which the reflecting surface of the third reflecting mirror and the reflecting surface of the fourth reflecting mirror face each other. Is a direction along the.

  According to this aspect, the first retroreflective unit can retroreflect light using two reflecting mirrors (that is, the first reflecting mirror and the second reflecting mirror). Similarly, the fourth retroreflective means can retroreflect light using two reflecting mirrors (that is, the third reflecting mirror and the fourth reflecting mirror).

  The first retroreflective means preferably includes two or less reflecting mirrors (in other words, three or more favoring mirrors are not included). Similarly, the second retroreflective means preferably includes two or less reflecting mirrors (in other words, does not include three or more favor reflecting mirrors). An example of retroreflective means including two or less reflecting mirrors is a right-angle prism.

<5>
In another aspect of the optical delay device of the present embodiment, each of the first retroreflective means and the second retroreflective means is based on the retroreflective of the light by the first retroreflective means and the second retroreflective means. The plurality of light retroreflections are alternately arranged a plurality of times, and the second direction of at least one of the plurality of first retroreflection means is the plurality of the plurality of first retroreflection means. The plurality of first retroreflective means and the plurality of second retroreflective means are arranged so as to cross the fourth direction in at least one second retroreflective means of the second retroreflective means.

  According to this aspect, the second direction in which the retroreflection of at least one of the plurality of first retroreflection means can be performed, and the first direction of at least one of the plurality of second retroreflection means. The first retroreflective means and the second retroreflective means are arranged so that the fourth direction in which the retroreflective means in the two retroreflective means can intersect (preferably orthogonal). As a result, even when a plurality of first retroreflective means and a plurality of second retroreflective means are provided, the various effects described above are favorably enjoyed.

(Embodiment of terahertz wave measuring apparatus)
<6>
The terahertz wave measuring apparatus according to the present embodiment is configured to generate a terahertz wave by irradiating the first laser beam and irradiate the second laser beam to the measurement target from the generating unit. Detecting means for detecting the terahertz wave irradiated in this manner, and retroreflecting one of the first laser light and the second laser light, thereby retroreflecting the first laser light and the second laser. A retroreflective device that guides at least one of the light to at least one of the generating unit and the detecting unit, wherein the retroreflective device includes the first laser beam and the second laser beam. Any one of the first retroreflective means for retroreflecting any one of the first laser light and the second laser light retroreflected by the first retroreflective means is used as the first retroreflective. A second retroreflecting means that retroreflects toward a stage, and at least one of the first retroreflecting means and the second retroreflecting means, the first retroreflecting means and the second retroreflecting means Moving means for moving the light incident on at least one side in the optical axis direction, wherein the first retroreflective means is configured to retroreflect by the inclination of the first retroreflective means along the first direction. Is impossible, while having the direction dependency that the retroreflection is possible even when the inclination of the first retroreflection means along the second direction different from the first direction occurs, The second retroreflective means makes the retroreflective impossible by the inclination of the second retroreflective means along the third direction, while the second retroreflective along the fourth direction different from the third direction. Even if the slope of the means occurs, the recursion Morphism has direction dependency that is possible, the and so intersects the second direction and the fourth direction, wherein the first retroreflector and the second retroreflector is arranged.

  According to the terahertz wave measuring apparatus of this embodiment, the operation of the generating unit, the detecting unit, and the retroreflective device causes the terahertz wave irradiated to the measurement object using the terahertz time-domain spectroscopy (Terahertz Time-Domain Spectroscopy). Is detected. The detected terahertz wave is used for analyzing the characteristics of the measurement object. Note that an existing detection method may be used as the terahertz wave detection method itself using the terahertz time domain spectroscopy. An outline of a terahertz wave detection method using terahertz time domain spectroscopy will be briefly described below.

  Specifically, the generation unit generates a terahertz wave by irradiating the generation unit with the first laser light as excitation light (for example, pump light). The terahertz wave generated by the generating means is irradiated to the measurement object.

  The detection means detects the terahertz wave reflected by the measurement object or transmitted through the measurement object by irradiating the detection means with the second laser light as excitation light (for example, probe light).

  In the present embodiment, the retroreflective device retroreflects either one of the first laser light and the second laser light. For example, the retroreflective device may retroreflect the second laser light. In this case, the retroreflected second laser light is guided to the detection means. Alternatively, for example, the retroreflective device may retroreflect the first laser light. In this case, the retroreflected first laser light is guided to the generating means. As a result, the retroreflective device can adjust the optical path length difference between the optical path of the first laser light and the optical path of the second laser light. In other words, the retroreflective device can set the optical path length difference between the optical path of the first laser beam and the optical path of the second laser beam to a desired value. Such adjustment of the optical path length difference is performed in order to suitably detect the waveform of the terahertz wave that appears in the order of sub-picoseconds.

  Here, the retroreflective device is the same as the retroreflective device of the present embodiment described above. Therefore, the retroreflective device can retroreflect light even when a retroreflective means such as a retroreflector that retroreflects light is tilted. As a result, either one of the first laser light and the second laser light reflected by the retroreflective device is appropriately applied to either the generation unit or the detection unit. Specifically, for example, one of the first laser beam and the second laser beam reflected by the retroreflective device is placed in the gap portion of one of the photoconductive antennas of the generating unit and the detecting unit. Properly irradiated. As a result, in the present embodiment, light is retroreflected as compared with the case where the second direction of the first retroreflective means and the fourth direction of the second retroreflective means do not intersect (for example, they are aligned). Even when a retroreflective means such as a retroreflective mirror (that is, the first retroreflective means) is inclined, the influence of the characteristics of the measurement object using the terahertz wave on the analysis accuracy is reduced.

  Incidentally, in response to the various aspects that can be adopted by the optical delay device of the present embodiment described above, the terahertz wave measuring apparatus of the present embodiment may also adopt various aspects.

  Such an operation and other advantages of the present embodiment will be further clarified from examples described below.

  As described above, the retroreflective device according to the present embodiment includes the first and second retroreflective means, and the second direction, which is the direction of the inclination of the first retroreflective means that enables retroreflective, and the retroreflective means. It intersects the fourth direction of the second retroreflective means that is enabled. The terahertz wave measuring device of this embodiment includes the retroreflective device of this embodiment. Therefore, light can be retroreflected even when a retroreflective means such as a retroreflector that retroreflects light is tilted.

  Hereinafter, examples will be described with reference to the drawings.

(1) First Example First, a terahertz wave measuring apparatus 100 according to a first example will be described with reference to FIGS.

(1-1) Configuration of Terahertz Wave Measuring Device First, the configuration of the terahertz wave measuring device 100 of the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a terahertz wave measuring apparatus 100 according to the first embodiment.

  As shown in FIG. 1, the terahertz wave measuring apparatus 100 irradiates the measurement target with the terahertz wave THz and transmits the terahertz wave THz transmitted through or reflected from the measurement target (that is, irradiated to the measurement target). Detected terahertz wave THz).

The terahertz wave THz is an electromagnetic wave belonging to a frequency region (that is, a terahertz region) around 1 terahertz (1 THz = 10 ¹² Hz). The terahertz region is a frequency region that combines light straightness and electromagnetic wave transparency. The terahertz region is a frequency region in which various substances have unique absorption spectra. Therefore, the terahertz wave measuring apparatus 100 can analyze the characteristics of the measurement object by analyzing the frequency spectrum of the terahertz wave THz applied to the measurement object.

  In order to acquire the frequency spectrum of the terahertz wave THz irradiated on the measurement object, the terahertz wave measuring apparatus 100 employs terahertz time-domain spectroscopy (Terahertz Time-Domain Spectroscopy). The terahertz time domain spectroscopy irradiates the measurement target with the terahertz wave THz and performs Fourier transform on the time waveform of the terahertz wave THz that has passed through the measurement target or reflected from the measurement target. This is a method for acquiring a spectrum (that is, amplitude and phase for each frequency).

  Here, since the period of the terahertz wave THz is a period on the order of subpicoseconds, it is technically difficult to directly detect the time waveform of the terahertz wave THz. Therefore, the terahertz wave measuring apparatus 100 indirectly detects the time waveform of the terahertz wave THz by adopting a pump-probe method based on time delay scanning.

  As shown in FIG. 1, a terahertz wave measuring apparatus 100 employing such a terahertz time-domain spectroscopy method and a pump-probe method includes a pulse laser apparatus 101 and a terahertz wave generating element which is a specific example of “generating means”. 110, a beam splitter 161, a reflecting mirror 162, a reflecting mirror 163, an optical delay device 120 which is a specific example of “retroreflective device”, and a terahertz wave detecting element 130 which is a specific example of “detecting means”. A bias voltage generation unit 141, an IV (current-voltage) conversion unit 144, a lock-in detection unit 145, and an arithmetic processing unit 150.

  The pulse laser device 101 generates pulse laser light LB in the sub-picosecond order or femtosecond order having light intensity corresponding to the drive current input to the pulse laser device 101. The repetition frequency of the pulse laser beam LB is about several tens of MHz. The pulse laser beam LB generated by the pulse laser device 101 enters the beam splitter 161 through a light guide (not shown) (for example, an optical fiber) and a lens (not shown).

  The beam splitter 161 splits the pulsed laser light LB into pump light LB1 which is a specific example of “first laser light” and probe light LB2 which is a specific example of “second laser light”. The pump light LB1 is incident on the terahertz wave generating element 110 through a lens (not shown). On the other hand, the probe light LB <b> 2 enters the optical delay device 120 through the reflecting mirror 162.

  The optical delay device 120 adjusts the difference (that is, the optical path length difference) between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. Specifically, the optical delay device 120 adjusts the optical path length between the optical path length of the pump light LB1 and the optical path length of the probe light LB2 by adjusting the optical path length of the probe light LB2. The timing at which the pump light LB1 enters the terahertz wave generation element 110 (or from the terahertz wave generation element 110) is adjusted by adjusting the optical path length difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. It is possible to adjust the relative shift amount between the timing at which the outgoing terahertz wave THz enters the terahertz wave detection element 130 and the timing at which the probe light LB2 enters the terahertz wave detection element 130. For example, when the optical path of the probe light LB2 is increased by 0.3 millimeters (however, the optical path length in the air) by the optical delay device 120, the timing at which the probe light LB2 enters the terahertz wave detection element 130 is delayed by 1 picosecond. Become. In this case, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is delayed by 1 picosecond. Considering that the terahertz wave THz having the same waveform repeatedly enters the terahertz wave detecting element 130 at intervals of about several tens of MHz, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is gradually shifted. Thus, the terahertz wave detection element 130 can indirectly detect the time waveform of the terahertz wave THz.

  FIG. 1 shows the terahertz wave measuring apparatus 100 in which the optical delay device 120 is disposed in the optical path of the probe light LB2. However, the optical delay device 120 may be disposed in the optical path of the pump light LB1 in addition to or instead of the optical path of the probe light LB2. In other words, in addition to or instead of adjusting the optical path length of the probe light LB2, the optical delay device 120 adjusts the optical path length of the pump light LB1 to thereby adjust the optical path length of the pump light LB1 and the optical path length of the probe light LB2. May be adjusted.

  In order to adjust the optical path length of the probe light LB2, the optical delay device 120 includes a movable retroreflector 121 which is a specific example of “first retroreflective means” and a specific example of “second retroreflective means”. A fixed retroreflector 122, a feed screw mechanism 123, and a motor 124 are provided.

  The movable retroreflector 121 retroreflects the probe light LB2 incident on the movable retroreflector 121. That is, the movable retroreflective mirror 121 reflects the probe light LB2 incident on the movable retroreflective mirror 121 in a direction parallel to the incident direction of the probe light LB2. In the first embodiment, the movable retroreflector 121 includes a first reflecting surface 121-1 and a second reflecting surface 121-2 that intersect at an angle of 90 degrees.

  Similarly, the fixed retroreflector 122 retroreflects the probe light LB2 incident on the fixed retroreflector 122. That is, the fixed retroreflector 122 reflects the probe light LB2 incident on the fixed retroreflector 122 in a direction parallel to the incident direction of the probe light LB2. In the first embodiment, the fixed retroreflector 122 includes a first reflecting surface 122-1 and a second reflecting surface 122-2 that intersect at an angle of 90 degrees (see FIG. 4 in addition to FIG. 1). ).

  The movable retroreflector 121 includes a feed groove that fits into the feed screw mechanism 123. As a result, the movable retroreflector 121 moves the optical path of the probe light LB2 in accordance with the rotation of the feed screw mechanism 123 driven by the motor 124 (specifically, the probe light LB2 when entering the movable retroreflector 121). The optical path moves along the vertical direction in FIG. However, the movable retroreflecting mirror 121 does not have to move (that is, it may be fixed).

  On the other hand, it is preferable that the fixed retroreflector 122 does not move (that is, is fixed). However, the fixed retroreflecting mirror 122 is along the optical path of the probe light LB2 (specifically, the optical path of the probe light LB2 when entering the fixed retroreflecting mirror 122 and in the vertical direction in FIG. 1). You may move.

  By such movement of the movable retroreflecting mirror 121, the optical path length of the probe light LB2 is adjusted.

  The movable retroreflector 121 is moved under the control of the arithmetic processing unit 150. That is, the arithmetic processing unit 150 controls the operation of the motor 124 by outputting a control signal that specifies the drive amount of the motor 124 to the motor 124.

  Here, an example of the optical path of the probe light LB2 in the optical delay device 120 will be described. In the example shown in FIG. 1, the probe light LB <b> 2 that enters the optical delay device 120 is first reflected by the first reflecting surface 121-1 of the movable retroreflector 121. At this time, the first reflecting surface 121-1 of the movable retroreflecting mirror 121 reflects the probe light LB2 toward the second reflecting surface 121-2 of the movable retroreflecting mirror 121. Thereafter, the probe light LB2 is reflected by the second reflecting surface 121-2 of the movable retroreflector 121. At this time, the second reflecting surface 121-2 of the movable retroreflecting mirror 121 reflects the probe light LB2 toward the first reflecting surface 122-1 of the fixed retroreflecting mirror 122. Thereafter, the probe light LB2 is reflected by the first reflecting surface 122-1 of the fixed retroreflector 122. At this time, the first reflecting surface 122-1 of the fixed retroreflecting mirror 122 reflects the probe light LB2 toward the second reflecting surface 122-2 of the fixed retroreflecting mirror 122. Thereafter, the probe light LB2 is reflected by the second reflecting surface 122-2 of the fixed retroreflector 122. At this time, the second reflecting surface 122-2 of the fixed retroreflecting mirror 122 reflects the probe light LB2 toward the second reflecting surface 121-2 of the movable retroreflecting mirror 121. Thereafter, the probe light LB2 is reflected by the second reflecting surface 121-2 of the movable retroreflector 121. At this time, the second reflecting surface 121-2 of the movable retroreflecting mirror 121 reflects the probe light LB2 toward the first reflecting surface 121-1 of the movable retroreflecting mirror 121. Thereafter, the probe light LB2 is reflected by the first reflecting surface 121-1 of the movable retroreflector 121. At this time, the first reflecting surface 121-1 of the movable retroreflecting mirror 121 reflects the probe light LB2 toward the outside of the optical delay device 120 (for example, the reflecting mirror 163).

  As described above, in the example illustrated in FIG. 1, the probe light LB <b> 2 propagates along the optical path that reciprocates between the movable retroreflector 121 and the fixed retroreflector 122 in the optical delay device 120. In order to propagate the probe light LB2 along the optical path that reciprocates between the movable retroreflecting mirror 121 and the fixed retroreflecting mirror 122, the movable retroreflecting mirror 121 and the fixed retroreflecting mirror 122 are the first of the movable retroreflecting mirror 121. It is preferable that the first reflecting surface 121-1 and the second reflecting surface 121-2 are arranged so that the first reflecting surface 122-1 and the second reflecting surface 122-2 of the fixed retroreflector 122 face each other. In particular, the movable retroreflector 121 and the fixed retroreflector 122 are configured so that the optical path of the probe light LB2 and the fixed retroreflector 122 receive the probe light LB2 when the movable retroreflector 121 retroreflects the probe light LB2. It is preferable that the probe light LB2 in a retroreflected state is arranged so as to be parallel (or aligned) with the optical path of the probe light LB2. As a result of the movable retroreflector 121 and the fixed retroreflector 122 being arranged in such a manner, the optical delay device 120 can retroreflect the probe light LB2.

  Here, in the first embodiment, in particular, the movable retroreflector 121 and the fixed retroreflector 122 are used to detect the terahertz wave THz detection accuracy by the terahertz wave detection element 130 (in other words, the characteristics of the measurement object by the terahertz wave measuring apparatus 100). Are arranged so as to satisfy a predetermined condition determined from the viewpoint of reducing the influence of the tilt of the movable retroreflecting mirror 121 (in other words, positional deviation). In other words, the movable retroreflector 121 and the fixed retroreflector 122 retroreflect the probe light LB2 even when the movable retroreflector 121 is tilted to the extent that the probe light LB2 cannot be retroreflected. The optical delay device 120 is arranged so as to satisfy a predetermined condition that is determined from the viewpoint of realizing the optical delay device 120 that can be used. The arrangement of the movable retroreflector 121 and the fixed retroreflector 122 determined from this point of view will be described in detail later with reference to FIG.

  The probe light LB2 emitted from the optical delay device 120 is incident on the terahertz wave detection element 130 via the reflecting mirror 163 and a lens (not shown).

  Here, the terahertz wave generating element 110 irradiated with the pump light LB1 and the terahertz wave detecting element 130 irradiated with the probe light LB2 will be described in more detail with reference to FIG. FIG. 2 is a perspective view showing the configuration of each of the terahertz wave generation element 110 and the terahertz wave detection element 130. The configurations of the terahertz wave generation element 110 and the terahertz wave detection element 130 illustrated in FIG. 2 are merely examples, and a photoconductive antenna or a photoconductive switch having a configuration different from the configuration illustrated in FIG. The terahertz wave detecting element 130 may be used.

  As shown in FIG. 2A, the terahertz wave generating element 110 includes a substrate 111, an antenna (in other words, a transmission line) 112, and an antenna (in other words, a transmission line) 113. Note that the X1, Y1, and Z1 axes in FIG. 2A correspond to three axes that intersect each other at an angle of 90 degrees.

  The substrate 111 is a semiconductor substrate such as a GaAs (Gallium Arsenide) substrate. Each of the antenna 112 and the antenna 113 is a monopole antenna having a shape extending in the longitudinal direction (specifically, the Z1 axis direction in FIG. 2A). The antenna 112 and the antenna 113 are disposed on the substrate 111 so as to be arranged in parallel along the short direction (specifically, the Y1 axis direction in FIG. 2A). A gap (that is, a gap) 114 of about several micrometers is secured between the antenna 112 and the antenna 113. Since the gap 114 is sandwiched between the antenna 112 and the antenna 113 extending in the longitudinal direction, the gap 114 also extends in the longitudinal direction (specifically, the Z1 axis direction in FIG. 2A). ing. Therefore, the antenna 112 and the antenna 113 as a whole constitute a dipole antenna.

  A bias voltage output from the bias voltage generation unit 141 is applied to the gap 114 via the antenna 112 and the antenna 113. When the pump light LB1 is irradiated to the gap 114 while the bias voltage is applied to the gap 114, carriers are generated in the terahertz wave generation element 110 by light excitation by the pump light LB1. As a result, the terahertz wave generating element 110 generates a pulse-shaped current signal in the order of subpicoseconds or in the order of femtoseconds corresponding to the generated carrier. As a result, the terahertz wave generation element 110 generates a terahertz wave THz resulting from the pulsed current signal.

  As shown in FIG. 2B, the terahertz wave detecting element 130 also has the same configuration as the terahertz wave generating element 110. That is, the terahertz wave detecting element 130 includes a substrate 131, an antenna (in other words, a transmission line) 132, and an antenna (in other words, a transmission line) 133. The substrate 131, the antenna 132, and the antenna 133 have the same configuration as the substrate 111, the antenna 112, and the antenna 113, respectively. Note that the X1, Y1, and Z1 axes in FIG. 2B also correspond to three axes that intersect each other at an angle of 90 degrees.

  When the probe light LB2 is irradiated to the gap 134, carriers are generated in the terahertz wave detection element 130 by light excitation by the probe light LB2. When the terahertz wave detecting element 130 is irradiated with the terahertz wave detection element 130 while the probe beam LB2 is irradiated on the gap 134, a current signal having a signal intensity corresponding to the light intensity of the terahertz wave THz is generated in the gap 134. To do. The current signal is output to the IV conversion unit 144 via the antenna 132 and the antenna 133.

  In FIG. 1 again, the terahertz wave THz emitted from the terahertz wave generating element 110 is irradiated onto the measurement object via an optical system (not shown) (for example, a lens). The terahertz wave THz applied to the measurement object is incident on the terahertz wave detection element 130 through a not-shown optical system (for example, a lens) as reflected light or transmitted light from the measurement object. As a result, the terahertz wave detection element 130 outputs a current signal having a signal intensity corresponding to the light intensity of the terahertz wave THz.

  The current signal output from the terahertz wave detection element 130 is converted into a voltage signal by the IV conversion unit 144. Thereafter, the lock-in detection unit 145 performs synchronous detection on the voltage signal using the bias voltage generated by the bias voltage generation unit 141 as a reference signal. As a result, the lock-in detection unit 145 detects the sample value of the terahertz wave THz. Thereafter, the lock-in detector 145 detects the time waveform of the terahertz waveform by repeating the same operation while appropriately adjusting the optical path length difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. can do. However, when a sufficient signal strength against noise is obtained, a DC voltage is output as a bias voltage from the bias voltage generation unit 141, and lock-in detection may not be used. Thereafter, the arithmetic processing unit 150 may acquire a frequency spectrum (that is, an amplitude and a phase for each frequency) of the terahertz wave by performing a Fourier transform on the detected time waveform of the terahertz waveform. Furthermore, the arithmetic processing unit 150 may analyze the characteristics of the measurement object by analyzing the frequency spectrum of the terahertz wave.

(1-2) Arrangement Modes of Movable Retroreflector and Fixed Retroreflector Subsequently , arrangement modes of the movable retroreflector 121 and the fixed retroreflector 122 will be described with reference to FIGS. 3 to 5. FIG. 3 is a plan view showing the optical path (incident optical path and reflected optical path) of the probe light LB2 with respect to the inclination (positional deviation) of the movable retroreflector 121. FIG. FIG. 4 is a perspective view showing an arrangement mode of the movable retroreflector 121 and the fixed retroreflector 122 in the first embodiment. FIG. 5 is a plan view showing an example of the optical path of the probe light LB2 when the movable retroreflector 121 is tilted in the optical delay device 120 of the first embodiment.

  The movable retroreflector 121 has a direction dependency in which whether or not the probe light LB2 can be appropriately retroreflected depends on the inclination direction of the movable retroreflector 121.

  Specifically, as shown in FIGS. 3A and 3B, each of the first reflecting surface 121-1 and the second reflecting surface 121-2 has two orthogonal axes X2 and A movable retroreflector 121 that is orthogonal to the plane defined by the Y2 axis and intersects each of the X2 axis and the Y2 axis at an angle of 45 degrees will be described as an example.

  Here, as shown in FIG. 3A, the movable retroreflector 121 is incident on the movable retroreflector 121 in a state where (i) the movable retroreflector 121 retroreflects the probe light LB2. The direction along the plane (X2-Y2 plane in FIG. 3A) including the incident optical path of the incoming probe light LB2 and the reflected optical path of the probe light LB2 emitted from the movable retroreflector 121 (Ii) A case is assumed in which the probe light LB2 is inclined along a direction orthogonal to the incident optical path and the reflected optical path (specifically, the Y2 axis direction in FIG. 3A). In other words, the movable retroreflector 121 has a direction orthogonal to the plane including the incident optical path and the reflected optical path of the probe light LB2 in a state where the movable retroreflector 121 retroreflects the probe light LB2 (specifically, Suppose a case in which it is tilted with the Z2 axis direction in FIG. In other words, the movable retroreflector 121 is along the direction in which the first reflecting surface 121-1 and the second reflecting surface 121-2 face each other (specifically, the Y2 axis direction in FIG. 3A). Assuming the case of tilting. In other words, the yaw direction based on the incident optical path of the probe light LB2 incident on the movable retroreflecting mirror 121 (however, the direction along the Z2 axis is the vertical direction, and the direction along the X2 axis is the front-back direction) , When the direction along the Y2 axis is the left-right direction (hereinafter the same), specifically, when the movable retroreflector 121 is tilted along the Y2 axis direction in FIG. Is assumed.

  In this case, as shown in the lower drawing of FIG. 3A, the movable retroreflector 121 can retroreflect the probe light LB2. Accordingly, assuming a comparative optical delay device having a reflecting mirror having only one reflecting surface instead of the fixed retroreflecting mirror 122, the comparative optical delay device may retroreflect the probe light LB2. it can. As a result, the irradiation position of the probe light LB2 on the terahertz wave detection element 130 is hardly displaced along the tilt direction of the movable retroreflector 121 (Y2 axis direction, yaw direction). That is, the movable retroreflector 121 has a relatively high deviation angle accuracy in the yaw direction with respect to the incident optical path of the probe light LB2 incident on the movable retroreflector 121.

  On the other hand, as shown in FIG. 3B, the movable retroreflecting mirror 121 has (i) the incident optical path and reflection of the probe light LB2 in a state where the movable retroreflecting mirror 121 retroreflects the probe light LB2. A case is assumed in which it is inclined along a direction (specifically, the Z2 axis direction in FIG. 3B) perpendicular to the plane including the optical path (X2-Y2 plane in FIG. 3B). In other words, the movable retroreflector 121 has a direction along a plane including (i) the incident optical path and the reflected optical path of the probe light LB2 in a state where the movable retroreflector 121 retroreflects the probe light LB2. (Ii) Assume a case where the probe light LB2 is tilted about the rotation center in the direction orthogonal to the incident optical path and the reflected optical path (specifically, the Y2 axis direction in FIG. 3B). In other words, the movable retroreflector 121 has a direction orthogonal to the direction in which the first reflecting surface 121-1 and the second reflecting surface 121-2 face each other (specifically, the Z2 axis in FIG. 3B). Suppose that it is tilted along (direction). In other words, along the pitch direction (specifically, the Z2 axis direction in FIG. 3B) with respect to the incident optical path of the probe light LB2 incident on the movable retroreflecting mirror 121, the movable retroreflecting mirror is used. Assume that 121 is tilted.

  In this case, as shown in the lower drawing of FIG. 3B, the movable retroreflector 121 cannot retroreflect the probe light LB2. Specifically, the reflected light path of the probe light LB2 emitted from the movable retroreflecting mirror 121 is inclined with respect to the incident optical path of the probe light LB2 incident on the movable retroreflecting mirror 121. (The Z2 axis direction, which is the pitch direction). Therefore, assuming a comparative optical delay device having a reflecting mirror having only one reflecting surface instead of the fixed retroreflecting mirror 122, the reflection of the probe light LB2 emitted from the optical delay device of the comparative example is assumed. The optical path is also gradually shifted along the direction of inclination of the movable retroreflector 121 (Z2 axis direction, pitch direction) with respect to the incident optical path of the probe light LB2 incident on the optical delay device of the comparative example. It will be. As a result, the irradiation position of the probe light LB2 on the terahertz wave detection element 130 is also displaced along the tilt direction of the movable retroreflector 121 (Z2 axis direction, pitch direction). That is, the movable retroreflective mirror 121 has a relatively low declination accuracy in the pitch direction with reference to the incident optical path of the probe light LB2 incident on the movable retroreflective mirror 121.

  In this manner, the movable retroreflector 121 cannot retroreflect the probe light LB2 due to the inclination of the movable retroreflector 121 along the pitch direction with respect to the incident optical path of the probe light LB2, while the probe light LB2 cannot be retroreflected. The probe beam LB2 has a direction dependency that the probe light LB2 can be continuously retroreflected even if the movable retroreflector 121 is tilted along the yaw direction with respect to the incident light path of the LB2.

  Note that, similarly to the movable retroreflector 121, the fixed retroreflector 122 also determines whether or not the probe light LB2 can be appropriately retroreflected depending on the inclination direction of the fixed retroreflector 122. It has direction dependency. That is, assuming that the fixed retroreflector 122 is arranged in the same manner as the movable retroreflector 121 shown in FIG. 3, the fixed retroreflector along the pitch direction with the incident light path of the probe light LB2 as a reference is assumed. While the probe beam LB2 cannot be retroreflected due to the tilt of 122, the probe beam LB2 is retroreflected even when the tilt of the fixed retroreflector 122 along the yaw direction with respect to the incident optical path of the probe beam LB2 occurs. It has a direction dependency that can continue. However, the fixed retroreflector 122 is actually arranged in the manner shown in FIG. That is, the fixed retroreflector 122 is arranged in a different manner from the movable retroreflector 121. Therefore, assuming that the fixed retroreflector 122 is arranged in the manner shown in FIG. 4, the fixed retroreflector 122 substantially tilts the fixed retroreflector 122 along the yaw direction with respect to the incident optical path of the probe light LB2. As a result, the probe light LB2 cannot be retroreflected, but the probe light LB2 continues to be retroreflected even if the fixed retroreflector 122 is tilted along the pitch direction with respect to the incident optical path of the probe light LB2. It can also be said that it has direction dependency that it can.

  Here, the probe light LB2 may not be irradiated to the gap 134 of the terahertz wave detection element 130 due to the displacement of the irradiation position of the probe light LB2. As a result, the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 may be deteriorated. For this reason, in the first embodiment, in order to suppress the degradation of the analysis accuracy, instead of the fixed retroreflector 122, instead of the optical delay device of the comparative example having a reflector having only one reflecting surface, An optical delay device 120 including a movable retroreflector 121 and a fixed retroreflector 122 is used. In particular, in the first embodiment, the movable retroreflector 121 is considered in consideration of the direction dependency of the movable retroreflector 121 and the direction dependency of the fixed retroreflector 122 in order to suppress degradation of analysis accuracy. And a fixed retroreflector 122 is arranged in a suitable manner. More specifically, as shown in FIG. 4, the direction of the tilt of the movable retroreflector 121 that can retroreflect the probe light LB2 and the fixed retroreflector 122 that can retroreflect the probe light LB2. The movable retroreflector 121 and the fixed retroreflector 122 are arranged so that the direction of the inclination intersects (in the example shown in FIG. 4, it is orthogonal). FIG. 4 shows a fixed retroreflector 122 capable of retroreflecting the probe light LB2 while the direction of inclination of the movable retroreflector 121 capable of retroreflecting the probe light LB2 coincides with the Z2 axis direction. In this example, the direction of the inclination is coincident with the Y2 axis direction orthogonal to the Z2 axis direction.

  In the terahertz wave measuring apparatus 100 in which the movable retroreflector 121 and the fixed retroreflector 122 are arranged in such a manner, as shown in FIG. 5, the movable retroreflector 121 extends along the Z2 axis direction (pitch direction). Assume a tilted case. That is, it is assumed that the movable retroreflecting mirror 121 is tilted along a direction in which the probe light LB2 cannot be retroreflected.

  In this case, if there is no contrivance in the arrangement mode of the movable retroreflector 121 and the fixed retroreflector 122 (specifically, unless it has a positional relationship as shown in FIG. 4), the Z2 axis Due to the inclination of the movable retroreflector 121 along the direction (pitch direction), the reflected light path of the probe light LB2 emitted from the optical delay device 120 is the direction of the inclination of the movable retroreflector 121 (Z2 axis direction) And gradually deviate along the pitch direction). As a result, the irradiation position of the probe light LB2 on the terahertz wave detection element 130 is displaced along the tilt direction of the movable retroreflector 121 (that is, the Z2 axis direction (pitch direction)). Therefore, if there is no contrivance in the arrangement mode of the movable retroreflector 121 and the fixed retroreflector 122 (specifically, unless it has a positional relationship as shown in FIG. 4), the probe light LB2 May not be irradiated to the gap 134.

  However, in the first embodiment, as shown in FIG. 5, the probe light LB2 that has entered the optical delay device 120 is reflected by the movable retroreflector 121, so that the fixed retroreflector 122 along the optical path A is reflected. Head. It can be said that this optical path A is disturbed from the optical path when the probe light LB2 is retroreflected in a state where the movable retroreflector 121 is not tilted. Thereafter, the probe light LB <b> 2 is reflected by the fixed retroreflector 122 and travels along the optical path B toward the movable retroreflector 121. Here, considering that the fixed retroreflecting mirror 122 retroreflects the probe light LB2, the optical path B becomes parallel to the optical path A. As a result, the disturbance of the optical path of the probe light LB2 due to the inclination of the movable retroreflector 121 along the Z2 axis direction (pitch direction) is canceled by the re-reflection at the movable retroreflector 121 (in other words, Compensated).

  In other words, in the movable retroreflector 121, a total of two times, that is, when the probe light LB2 is reflected toward the fixed retroreflector 122 and when the probe light LB retroreflected by the fixed retroreflector 122 is reflected again. The incident light of the probe light LB2 is reflected. Then, when the probe light LB2 is reflected toward the fixed retroreflecting mirror 122, the optical path of the probe light LB2 is disturbed due to the inclination of the movable retroreflecting mirror 121 (that is, the optical path A is disturbed), but the fixed retroreflecting is performed. When the probe light LB2 retroreflected by the mirror 122 is reflected again, the disturbance of the optical path is canceled or compensated. That is, when the movable retroreflector 121 that performs the incident reflection (that is, a series of incident and reflected) of the probe light LB2 twice (or even times) is tilted, it is caused by the tilt of the movable retroreflector 121. The disturbance in the optical path of the probe light LB2 is preferably canceled or compensated.

  For this reason, even if it is a case where retroreflection becomes impossible if it sees with the movable retroreflection mirror 121 single-piece | unit, if it sees with the optical delay device 120 whole, retroreflection becomes possible. As a result, the influence of the tilt of the movable retroreflector 121 along the Z2 axis direction (pitch direction) on the detection accuracy of the terahertz wave THz by the terahertz wave detection element 130 is reduced. In other words, deterioration of the detection accuracy of the terahertz wave THz by the terahertz wave detecting element 130 due to the inclination of the movable retroreflector 121 along the Z2 axis direction (pitch direction) can be minimized. Therefore, the influence of the tilt of the movable retroreflector 121 along the Z2 axis direction (pitch direction) on the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 is reduced. In other words, degradation of the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 100 due to the inclination of the movable retroreflector 121 along the Z2 axis direction (pitch direction) can be minimized.

  The optical delay device 120 described above is merely an example, and an optical delay device different from the optical delay device 120 illustrated in FIG. 1 may be used. For example, as shown in FIG. 6, an optical delay device 120a having a rotating substrate 122a that can be rotated by the operation of a motor 124 (not shown) and a plurality of (four in FIG. 6) movable retroreflectors 121 is used. May be. In such an optical delay device 120a, the plurality of movable retroreflecting mirrors 121 are preferably arranged at equal intervals on a circle C centered on the rotation axis of the rotating substrate 122a. Therefore, each of the plurality of movable retroreflecting mirrors 121 circulates on the circle C as the rotating substrate 122a rotates.

  Even in such an optical delay device 120a, whether or not each movable retroreflector 121 can appropriately retroreflect the probe light LB2 depends on the inclination direction of the movable retroreflector 121. It has a direction dependency that is determined.

  Specifically, as shown in FIG. 7A, the description will be focused on one movable retroreflector 121. The plane including the incident optical path and the reflected optical path of the probe light LB2 in a state where the movable retroreflector 121 retroreflects the probe light LB2 (X2-Y2 plane in FIG. 7A). ) Is assumed to be tilted along a direction perpendicular to (specifically, the Z2 axis direction in FIG. 7A). Specifically, as shown in the upper drawing of FIG. 7A, as an initial state, it is assumed that the movable retroreflector 121 is inclined so as to have an angle of α degrees with respect to the Z2 axis direction. Furthermore, as shown in the lower drawing of FIG. 7A, as an initial state, a line connecting the center of the rotating substrate 122a and the movable retroreflector 121 is assumed to coincide with the Y2 axis direction.

  In this case, as shown in the upper drawing of FIG. 7A, the movable retroreflector 121 cannot retroreflect the probe light LB2. Specifically, the reflected light path of the probe light LB2 emitted from the movable retroreflector 121 has an angle of 2α degrees with respect to the incident light path of the probe light LB2 incident on the movable retroreflector 121. become.

  Based on such an initial state, a state is assumed in which the rotating substrate 122a is rotated by θ degrees as shown in FIG. 7B. That is, it is assumed that a line connecting the center of the rotating substrate 122a and the movable retroreflecting mirror 121 intersects at an angle of θ degrees with respect to the Y2 axis direction.

  In this case, as shown in the upper drawing of FIG. 7B, the movable retroreflective mirror 121 is inclined so as to have an angle of β degrees with respect to the Z2 axis direction as the rotating substrate 122a rotates. Become. This angle β is expressed by a mathematical formula: β = arctan (tan α × cos θ). That is, it can be seen that the angle β varies depending on the rotation angle θ of the rotating substrate 122a. Therefore, the irradiation position of the probe light LB2 on the terahertz wave detection element 130 also depends on the tilt direction of the movable retroreflector 121 (Z2 axis direction, pitch direction) and on the rotation angle of the rotating substrate 122a. The position is displaced by the amount of displacement.

  Even when such an optical delay device 120a is used, the direction of the tilt of the movable retroreflector 121 that can retroreflect the probe light LB2 and the fixed retroreflection that can retroreflect the probe light LB2. The movable retroreflector 121 and the fixed retroreflector 122 are arranged so that the direction of inclination of the mirror 122 intersects. As a result, the various effects described above are favorably enjoyed.

  In the above description, an example in which the optical delay device 120 is applied to the terahertz wave measuring apparatus 100 is used. However, the optical delay device 120 may be applied to various devices other than the terahertz wave measuring device 100 (for example, an optical interferometer, optical coherent tomography, and other optical devices).

(2) Second Example Next, a terahertz wave measuring apparatus 200 according to a second example will be described with reference to FIG. FIG. 8 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus 200 according to the second embodiment. In addition, about the same structure and operation | movement as the terahertz wave measuring apparatus 100 of 1st Example, the same referential mark is attached | subjected and those detailed description is abbreviate | omitted.

  As shown in FIG. 8, in the terahertz wave measuring apparatus 200 of the second embodiment, an optical fiber 201 as a light guide is disposed between a beam splitter 161 and a terahertz wave generating element 110, and a reflecting mirror 163 and terahertz wave detection are performed. It differs from the terahertz wave measuring apparatus 100 of the first embodiment in that an optical fiber 202 as a light guide is disposed between the element 130. That is, in the terahertz wave measuring apparatus 200 of the second embodiment, the pump light LB1 is irradiated to the terahertz wave generating element 110 via the optical fiber 201, and the probe light LB2 is irradiated to the terahertz wave detecting element 130 via the optical fiber 202. This is different from the terahertz wave measuring apparatus 100 of the first embodiment. Other configurations of the terahertz wave measuring apparatus 200 of the second embodiment may be the same as other configurations of the terahertz wave measuring apparatus 100 of the first embodiment.

  By arranging such an optical fiber 201 and optical fiber 202, there is a very useful advantage in practice that the degree of freedom of arrangement of various components constituting the terahertz wave measuring apparatus 200 can be increased.

  On the other hand, when the optical fiber 201 and the optical fiber 202 are disposed, coupling between the pump light LB1 and the optical fiber 201 and coupling between the probe light LB2 and the optical fiber 202 are necessary. That is, it is necessary that the pump light LB1 is suitably applied to the core of the optical fiber 201 and the probe light LB2 is suitably applied to the core of the optical fiber 202. By the way, the size of the gap 134 of the terahertz wave detecting element 130 (for example, the length in the Z1 axis direction in FIG. 2) is about several tens of microns, whereas the diameter of the core of the single mode optical fiber 202 is 10. Less than a micron. Therefore, the terahertz wave measuring apparatus 200 of the second embodiment is compared with the terahertz wave measuring apparatus 100 of the first embodiment that irradiates the terahertz wave detecting element 130 with the probe light LB2 without arranging the optical fiber 202. The influence of the deterioration in the analysis accuracy of the characteristics of the measurement object due to the disturbance of the optical path of the probe light LB2 due to the inclination of the movable retroreflector 121 described above may increase. However, in the second embodiment, as described above, the optical path of the probe light LB2 is hardly disturbed due to the tilt of the movable retroreflector 121 described above (in other words, compensated or offset). Therefore, the coupling between the probe light LB2 and the optical fiber 202 is preferably performed. As a result, degradation of the analysis accuracy of the characteristics of the measurement object by the terahertz wave measuring apparatus 200 due to the tilt of the movable retroreflector 121 can be minimized.

(3) Third Example Next, a terahertz wave measuring apparatus 300 of a third example will be described with reference to FIG. FIG. 9 is a perspective view showing an arrangement mode of the movable retroreflector 121 and the fixed retroreflector 122 in the third embodiment.

  As shown in FIG. 9, the terahertz wave measuring apparatus 300 according to the third embodiment has the terahertz wave according to the first embodiment in that the configuration of the optical delay device 320 is different from the configuration of the optical delay device 120 according to the first embodiment. Different from the measuring device 100. Other configurations of the terahertz wave measuring apparatus 300 of the third embodiment may be the same as other configurations of the terahertz wave measuring apparatus 100 of the first embodiment.

  Specifically, as shown in FIG. 9, the optical delay unit 320 includes two movable retroreflectors 121 (that is, movable retroreflectors 121a and 121b) and two fixed retroreflectors 122 (that is, fixed recursors). Reflecting mirrors 122a and 122b). As a result, the probe light LB2 incident on the optical delayer 320 is converted into a movable retroreflector 121a, a fixed retroreflector 122a, a movable retroreflector 121b, a fixed retroreflector 122b, a movable retroreflector 121b, and a fixed retroreflector 122a. And, by being retroreflected in this order by the movable retroreflector 121a, it goes to the outside of the optical delay device 320. That is, in the optical delay device 320, the probe light LB2 propagates along an optical path that reciprocates a plurality of times between the movable retroreflectors 121 and 121b and the fixed retroreflectors 122a and 122b.

  Note that the optical delay device 320 may include three or more movable retroreflecting mirrors 121. Similarly, the optical delay device 320 may include three or more fixed retroreflectors 122.

  In the terahertz wave measuring apparatus 300 of the third embodiment, the amount of optical delay given to the optical path length of the probe light LB2 can be relatively increased. In other words, the optical path length of the probe light LB2 can be adjusted larger.

  In the third embodiment, particularly, at least one fixed retroreflective mirror 122 out of the two fixed retroreflective mirrors 122 has an inclination direction capable of retroreflecting the probe light LB2, and two movable retroreflective reflections. The two movable retroreflectors 121 and the two fixed retroreflectors 122 are arranged so that the direction of the inclination in which the probe light LB2 can be retroreflected in at least one movable retroreflector 121 of the mirrors 121 intersects. Is arranged. For example, in the example shown in FIG. 9, the direction of the inclination in which the probe light LB2 can be retroreflected in the fixed retroreflector 122b located at the last stage in the forward path or the first stage in the return path among the optical paths of the probe light LB2 (FIG. 9 in the Z2 axis direction) and an inclination direction (FIG. 9) in which the probe light LB2 can be retroreflected in the movable retroreflector 121b facing the fixed retroreflector 122b along the optical path of the probe light LB2. Two movable retroreflecting mirrors 121 and two fixed retroreflecting mirrors 122 are arranged so as to intersect with each other.

  By arranging the two movable retroreflecting mirrors 121 and the two fixed retroreflecting mirrors 122 in this way, the terahertz wave measuring apparatus 100 of the first embodiment can also enjoy the terahertz wave measuring apparatus 300 of the third embodiment. The various effects which can be enjoyed suitably. In other words, for example, even if the retroreflection is impossible when viewed by the movable retroreflector 121 alone due to the inclination of one or both of the movable retroreflectors 121a and 121b, the optical delay device When viewed as a whole, retroreflection is possible.

  Further, the present invention can be appropriately changed without departing from the gist or the idea of the invention that can be read from the claims and the entire specification, and a retroreflective device terahertz wave measuring device with such a change is also included in the present invention. It is included in the technical idea.

100, 200 Terahertz wave measuring device 101 Pulse laser device 110 Terahertz wave generating element 111 Substrate 112, 113 Antenna 114 Gap 120, 320 Optical delay device 121 Movable retroreflector 122 Fixed retroreflector 123 Feed screw mechanism 124 Motor 130 Terahertz wave detection Element 131 Substrate 132, 133 Antenna 134 Gap 141 Bias voltage generator 144 I-V converter 145 Lock-in detector 150 Arithmetic processor 161 Beam splitter 162, 163 Reflector LB Pulse laser light LB1 Pump light LB2 Probe light THz Terahertz wave

Claims (6)

A retroreflective device that retroreflects incident light,
First retroreflective means for retroreflecting the light;
Second retroreflective means for retroreflecting the light retroreflected by the first retroreflective means toward the first retroreflective means;
At least one of the first retroreflective means and the second retroreflective means is arranged in the optical axis direction of the light incident on at least one of the first retroreflective means and the second retroreflective means. And moving means for moving,
The first retroreflective means cannot perform the retroreflection due to the inclination of the first retroreflective means along the first direction, while the first retroreflective means along the second direction different from the first direction. It has a direction dependency that the retroreflection is possible even when the tilt of the reflecting means occurs,
While the second retroreflective means makes the retroreflective impossible by the inclination of the second retroreflective means along the third direction, the second retroreflective means along a fourth direction different from the third direction. It has a direction dependency that the retroreflection is possible even when the tilt of the reflecting means occurs,
The retroreflective device, wherein the first retroreflective means and the second retroreflective means are arranged so that the second direction and the fourth direction intersect. The retroreflective device according to claim 1, wherein the first retroreflective means and the second retroreflective means are arranged so that the second direction and the fourth direction are orthogonal to each other. In the first direction, the light retroreflected by the first retroreflective means and the optical path of the light incident on the first retroreflective means in a state where the first retroreflective means retroreflects the light. A direction different from the direction along the plane including the optical path of
In the second direction, the light retroreflected by the optical path of the light incident on the first retroreflective means and the first retroreflective means in a state where the first retroreflective means retroreflects the light. Direction along a plane including the optical path of
In the third direction, the light retroreflected by the optical path of the light incident on the second retroreflective means and the second retroreflective means in a state where the second retroreflective means retroreflects the light. A direction different from the direction along the plane including the optical path of
In the fourth direction, the light retroreflected by the optical path of the light incident on the second retroreflective means and the second retroreflective means in a state where the second retroreflective means retroreflects the light. The retroreflective device according to claim 1, wherein the retroreflective device is in a direction along a plane including the optical path. The first retroreflecting means includes a first reflecting mirror and a second reflecting mirror having a reflecting surface that intersects the reflecting surface of the first reflecting mirror at an angle of 90 degrees.
The second retroreflective means includes a third reflecting mirror and a fourth reflecting mirror having a reflecting surface that intersects at an angle of 90 degrees with respect to the reflecting surface of the third reflecting mirror,
The first direction is a direction in which the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror cross each other.
The second direction is a direction along a direction in which the reflecting surface of the first reflecting mirror and the reflecting surface of the second reflecting mirror face each other.
The third direction is a direction in which the reflecting surface of the third reflecting mirror and the reflecting surface of the fourth reflecting mirror intersect each other.
4. The fourth direction according to claim 1, wherein the fourth direction is a direction along a direction in which a reflecting surface of the third reflecting mirror and a reflecting surface of the fourth reflecting mirror face each other. 5. The retroreflective device described. Each of the first retroreflective means and the second retroreflective means alternately repeats the light retroreflected by the first retroreflective means and the light retroreflected by the second retroreflective means a plurality of times. Are arranged in a number,
The second direction in at least one of the plurality of first retroreflective means is the fourth direction in at least one second retroreflective means of the plurality of second retroreflective means. The retroreflective device according to any one of claims 1 to 4, wherein the plurality of first retroreflective means and the plurality of second retroreflective means are arranged so as to intersect with each other. Generating means for generating a terahertz wave by being irradiated with the first laser beam;
Detecting means for detecting the terahertz wave irradiated to the measurement object from the generating means by being irradiated with the second laser beam;
By retroreflecting either one of the first laser light and the second laser light, any one of the first laser light and the second laser light retroreflected is converted into the generation unit and the A retroreflective device leading to at least one of the detection means,
The retroreflective device is
First retroreflection means for retroreflecting any one of the first laser light and the second laser light;
Second retroreflective means for retroreflecting either one of the first laser light and the second laser light retroreflected by the first retroreflective means toward the first retroreflective means;
At least one of the first retroreflective means and the second retroreflective means is arranged in the optical axis direction of the light incident on at least one of the first retroreflective means and the second retroreflective means. And moving means for moving,
The first retroreflective means cannot perform the retroreflection due to the inclination of the first retroreflective means along the first direction, while the first retroreflective means along the second direction different from the first direction. It has a direction dependency that the retroreflection is possible even when the tilt of the reflecting means occurs,
While the second retroreflective means makes the retroreflective impossible by the inclination of the second retroreflective means along the third direction, the second retroreflective means along a fourth direction different from the third direction. It has a direction dependency that the retroreflection is possible even when the tilt of the reflecting means occurs,
The terahertz wave measuring apparatus, wherein the first retroreflective means and the second retroreflective means are arranged so that the second direction and the fourth direction intersect.

Images