JPH09246644A - Infrared-radiation emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of optical devices, such as an MLN and a grading optical device, and to reduce the manhour of adjustment in an infrared-radiation emitting device by a method wherein an optical parametric amplitude is performed using the emitted light of a first optical system as pumping light and using the emitted light of a second optical system as seed light and infrared radiation is outputted as idler light. SOLUTION: Seed light (ω2) generated by a second optical system 110 is reflected by a mirror 24 and is incided in a dichroic mirror 34, while pumping light (ω1) generated by a first optical system 100 is also incided in the mirror 34. The seed light and the pumping light are incided in an MLN 36 at a phase matching angle. Then, with the pumping light transmitted the MLN 36 reflected by a dichroic mirror 38, signal light and idler light are transmitted the mirror 38. The pumping light is projected on a non-reflector 42 by the mirror 38. On the other hand, the idler light only is transmitted a Ge element 44 and is outputted as infrared radiation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for generating infrared light by utilizing optical parametric amplification, and more particularly, to reducing the number of adjustment steps for various optical devices constituting the apparatus. The present invention relates to a device for generating infrared light.

[0002]

2. Description of the Related Art Light in the infrared region (2 to 20 (μm)) is
Since it is suitable for detecting vibration spectra of main molecules, it can be applied to various fields including evaluation by optical methods such as a film formation process (chemical reaction in CVD, etching, etc.) Devices that convert the wavelength of laser light in the region or near-infrared region and generate infrared light having a wavelength of 2 (μm) or more have been actively developed.

[0003] In order to perform such wavelength conversion, an apparatus using an optical parametric effect or optical parametric amplification has been proposed. The optical parametric effect is obtained by injecting pump light (angular frequency ω1) into a non-linear optical element fixed to a rotary stage or the like and adjusting the rotary stage to set the incident angle of the pump light so as to satisfy the phase matching condition. , Signal light (angular frequency ω2) and idler light (angular frequency ω3: ω2> ω3, ω = ω2 + ω3
). According to this effect, even if the wavelength of the pump light is fixed, the rotation stage is adjusted,
By changing the incident angle of the pump light to the nonlinear optical element while satisfying the phase matching condition, it becomes possible to change the wavelengths of the idler light and the signal light.

Also, optical parametric amplification (OPA)
Is to input pump light (angular frequency ω1) and seed light (seeding light: angular frequency ω2 or ω3) to a nonlinear optical element fixed to a rotary stage or the like, and adjust the rotary stage to adjust the incident angle of the pump light. The signal light (angular frequency ω2) and the idler light (angular frequency ω3: ω), which are amplified and become strong light, are set by satisfying the phase matching condition.
2> ω3, ω1 = ω2 + ω3). Also in optical parametric amplification, by adjusting the rotation stage and changing the incident angle of the pump light to the nonlinear optical element while satisfying the phase matching condition, the seed light can be obtained under the phase matching condition determined by the pump light and the seed light. To amplify.

Now, a conventional example of an infrared light generating apparatus utilizing such an optical parametric effect and optical parametric amplification will be described with reference to the drawings. FIG. 7 shows a configuration example of a conventional infrared light generation device.

The present apparatus utilizes a pump light generator 17 for generating pump light that is visible or near-infrared light, a seed light generator 19 for generating seed light from the pump light, and optical parametric amplification. An OPA unit 15 that generates infrared light and an optical system that delays pump light are configured.

The pump light generator 17 includes a pump laser 12 for generating infrared laser light having a fixed wavelength, and a lens 1 (focal length 1 (m)) for narrowing the laser light. The seed light generation unit 19 also includes a nonlinear optical element MLN1 (2) (lithium niobate LiNBO ₃ and magnesium oxide MgO ₃ ) that has an optical parametric effect of generating signal light and idler light based on the incident pump light. And the output idler light (signal light)
Focusing lens 3 (focal length 70 (mm))
It comprises a mirror 5 for reflecting the condensed light and a grating 4 for selecting light of a predetermined wavelength. Although not shown, the MLN 1 is fixed to a rotary stage, and the angle of incidence of the pump light transmitted through the beam splitter 6 can be adjusted by operating the rotary stage. The grating 4 is also fixed to the rotating stage, and by operating the rotating stage, two types of idler light (signal light) reflected by the mirror 5 are obtained.
Can be selected.

Further, the OPA section 15 includes a slit 10 for limiting an area to be irradiated with light, and an MLN 2 (11) for receiving the irradiated light and performing optical parametric amplification. Although not shown, the MLN 2 is fixed to a rotary stage, and the angle of incidence of the light passing through the slit 10 can be adjusted by operating the rotary stage.

Now, the principle of operation of generating infrared light in such an optical system will be described. First, the laser light output from the pump laser 12 is loosely narrowed by the collimating lens 1, and the narrowed light is split into two optical paths by the beam splitter 6. The light forming one optical path is collected again by the condenser lens 2 (focal length 200 (mm)), reflected by the mirror 8 after being given a predetermined time delay by the delay prism 7, and further reflected by the mirror 8.
OPA unit 1 reflected by dichroic mirror 9
5 is projected. The delay given by the delay prism 7 can be adjusted by moving the delay prism 7 by a moving mechanism (not shown).

On the other hand, light forming another optical path (angular frequency ω
1) is a signal light (angular frequency ω2) and an idler light (angular frequency ω3) due to the optical parametric effect of the MLN1.
: Ω2> ω3, ω1 = ω2 + ω3). Then, the signal light and the idler light are reflected by the mirror 5,
Either the signal light or the idler light is selected by the grating 4 and is emitted to the OPA unit 15 via the dichroic mirror 9. Therefore, the dichroic mirror 9 has a function of projecting the optical path of the pump light delayed by the delay and the optical path of the light selected by the grating 4 to the OPA unit 15.

Then, the light projected on the OPA unit 15 is applied to the MLN 2 through the slit 10. MLN2
Is the pump light and the seed light (ML) generated by the seed light generation unit 19.
The signal light (angular frequency ω2) and the idler light (angular frequency ω3: ω2> ω3) are generated by the parametric amplification by the optical parametric effect of N1 and the signal light or idler light selected by the grating 4.
, Ω1 = ω2 + ω3).

Further, signal light or idler light is selected by a light selecting element (not shown) and output as infrared light. Some conventional devices obtain infrared light in this way.

[0013]

However, in such an apparatus, when changing the wavelength of infrared light, the incident angle of the pump light with respect to the MLN1 is changed while satisfying the phase matching condition, and the light is generated by the optical parametric effect. In order to change the angular frequency (corresponding to the wavelength) of the idler light (or signal light) to be changed, the rotary stage had to be operated to finely adjust the incident angle, which required a huge amount of work. .

Further, for performing an adjustment operation by operating a rotary stage for fixing the grating 4 in accordance with a change in the angular frequency of the idler light (or signal light) generated by the optical parametric effect of the MLN 1, and for performing an optical parametric amplification. In addition, an adjustment operation by operating the rotary stage for fixing the MLN 2 occurs, and the direction of the light output from the crystal changes with the rotation of the MLN 2. In order to output infrared rays in the same optical path, a dummy crystal is required. In order to compensate for this, and to change the wavelength of the infrared light to be output, there is a problem that many work steps are required.

In addition, there has been a demand for the use of a large number of optical devices such as the MLN and the grating 4 and the formation of a delay optical path, resulting in a large device size and a reduction in the size of the device.
Therefore, an object of the present invention is to provide an infrared light generation device in which the number of optical devices such as MLNs and gratings is reduced and the number of adjustment steps of the device is reduced.

[0016]

SUMMARY OF THE INVENTION In order to solve the above problems and achieve the object of the present invention, the invention according to claim 1 is an apparatus for generating infrared light by using optical parametric amplification, wherein the apparatus generates infrared light. A first optical system that outputs a pulse at a predetermined cycle;
Light having a longer wavelength than the light can be selected within a predetermined wavelength range,
A second optical system that outputs a pulse of light of the selected wavelength in synchronization with the pulse, an optical path alignment optical system that performs optical path alignment of both optical systems, and receives light output from the optical path alignment optical system; Pump light output from the first optical system, and
A nonlinear optical element having a function of performing optical parametric amplification using the output light of the second optical system as seed light and outputting infrared light as idler light; and the nonlinear optical element determined by the wavelength of light of the first optical system. In the dependence characteristic of the phase matching angle of the idler light (or signal light) wavelength exhibited by the optical element, the phase at which two points at which the derivative of the phase matching angle change with respect to the idler light (or signal light) wavelength change becomes zero occurs. An infrared light generation device comprising: an adjustment mechanism for adjusting an arrangement state of the nonlinear optical element so that the pump light is incident on the nonlinear optical element at a matching angle.

The invention according to claim 1 is a pulse light generating apparatus, but other modes for generating CW infrared light are also conceivable. That is, the invention according to claim 2 is an apparatus for generating infrared light using optical parametric amplification, comprising: a first light source for outputting light; and a longer wavelength than light output from the first light source. Is selectable within a predetermined wavelength range, a second light source that outputs light of the selected wavelength, an optical path alignment optical system that performs optical path alignment of both light sources, and a light output from the optical path alignment optical system. A non-linear optical element having a function of receiving, outputting pump light as output light of the first light source, performing optical parametric amplification using output light of the second light source as seed light, and outputting infrared light as idler light; In the dependence characteristic of the phase matching angle of the idler light (or signal light) wavelength exhibited by the nonlinear optical element determined by the wavelength of the first light source, the phase matching angle change with respect to the idler light (or signal light) wavelength change Fine That the coefficient is zero 2
An infrared light generation device comprising: an adjustment mechanism for adjusting an arrangement state of the nonlinear optical element so that the pump light is incident on the nonlinear optical element at a phase matching angle at which a point occurs.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a drawing showing a configuration example of an apparatus according to an embodiment of the present invention.

The present apparatus comprises a first optical system 100 for outputting a pulse of light at a predetermined cycle, a light having a wavelength longer than the first light within a predetermined wavelength range, and a light having a selected wavelength being output at the pulse output. A second optical system 110 that outputs a pulse in synchronization with
Mirror 24 that reflects output light from second optical system 110
And a dichroic mirror 3 functioning as an optical path alignment optical system for aligning the optical path of the light reflected by the mirror 24 with the optical path of the light output from the first optical system 100.
4, an MLN 36 that is a nonlinear optical element that performs optical parametric amplification using light projected through the dichroic mirror 34, and an idler light (or signal light) output from the MLN 36, and A dichroic mirror 38 that reflects the pump light component, a non-reflector 42 that does not reflect the unnecessary pump light reflected by the dichroic mirror 38, and Ge (germanium) that transmits only idler light output from the MLN 36
The device includes an element 44, an adjustment mechanism 50 that fixes the MLN 36 and can adjust a phase matching angle of light applied to the MLN 36, and a timing generator 40 for generating synchronized pulse light.

Hereinafter, main components of the apparatus will be described. The first optical system includes a TiS laser (titanium sapphire laser) 30 and an optical amplifier 32 that amplifies the laser light and outputs a pulse.

As an example, the TiS laser 30 has a pulse width of 2 (ps), a repetition frequency of 82 (Hz), and an output of 10
(NJ) and a wavelength of 778 (nm). The optical amplifier 32 has a wavelength 77 output from the TiS laser 30.
8 (nm) pulsed light, average output 1 (mJ / pulse)
And output as a 10 (Hz) repetitive pulse (pulse width 2 (ps)). In addition, the optical amplifier 32
10 (Hz) by the timing generator 40
Is controlled so as to output a repetition pulse of.

The optical amplifier 32 is usually called a "regeneration amplifier", and its configuration is described, for example, in "Laser Science Research,
NO. 16 (1994) "and other known devices. An outline of the configuration is as follows. That is, TiS functioning as a mode-locked laser
The pulse light output from the laser 30 is supplied to a built-in YAG laser for amplification and excitation (pulse width 10 (ns), repetition frequency 10 (Hz), output 30 (mJ), wavelength 532 (n
m)) is cut out at a repetition frequency of 10 (Hz), and the cut out pulse light is amplified by an optical resonator composed of a plurality of mirrors, TiS (titanium sapphire) crystal, or the like, and the amplified light is output. . In addition, the timing generator 40 drives the oscillation drive unit included in the YAG laser for amplification and excitation and the optical resonator in order to cut out the pulse light output from the TiS laser 30.

The output light of the optical amplifier 32 amplified in this manner becomes pump light. Next, the second optical system has a Y
An OPO (Optica) that uses an AG laser (yag laser) 20 and the light of the laser as pump light, outputs infrared light having a wide wavelength range of output light and a longest wavelength of about 1.8 (μm).
l Parametric Oscillator: comprises an optical parametric oscillator 22.

The YAG laser 20 is a laser light source that is excited by a built-in flash lamp (not shown) and is switched by a built-in Q switch (not shown). Is output. The third harmonic, for example, can be obtained by the structure having a non-linear optical element ₂ 0 _4, etc. BaB the output position of the laser beam. Specifically, the second harmonic may be generated by a nonlinear optical element, and a laser beam as a fundamental wave may be superimposed on the second harmonic. It is to be noted that such a configuration is publicly known and will not be described in detail. When the timing generator 40 drives the flash lamp and the Q switch, the pulse light is output. The pulse repetition cycle is 10 (Hz), and the pulse light is output in synchronization with the output of the pump light.

As an example of the YAG laser 20,
The pulse width is 9 to 12 (ns), the output is 1.5 (J), and the wavelength is 1.06 (μm).
One that outputs light converted to a third harmonic having a wavelength of 5 (mJ) and a wavelength of 335 (nm) is exemplified.

The OPO 22 has a non-linear optical element such as BBO (BaB ₂ O ₄ ) exhibiting an optical parametric effect inside, and uses the third harmonic of the YAG laser 20 as pump light.
The signal light (440 to 690 (nm)) and the idler light (735 to 1800 (nm)) are obtained, and the idler light (735 to 1800) is selected by an optical device capable of selecting only near infrared.
800 (nm)) or signal light.

As an example of the characteristics of the OPO 22, a pulse width of 3 to 7 (ns) and a pulse repetition period of 10 (H
z), output 5 to 50 (mJ), oscillation bandwidth 0.2 (1
/ Cm) and the selectable wavelength range is from 0.73 to
1.8 (μm). Note that B in the OPO laser 22
The BO is rotatably provided by an operation dial or the like, and the wavelength of the idler light can be changed within a wavelength range of 0.73 to 1.8 (μm) by rotating the BBO. As described above, by setting the wavelength variable range of the OPO 22 to include a longer wavelength region than the wavelength of the pump light output from the first optical system, ω1
> Ω2 (angular frequency of ω1 pump light, angular frequency of ω2 seed light)
Thus, optical parametric amplification can be performed.

Note that the output of the OPO 22 becomes seed light,
About 1 (%) of the output power of PO22, that is, 0.05
The power of about (mJ) is the power of the seed light. Next, the MLN 36, which is a nonlinear optical element, is made of lithium niobate (l
A crystal obtained by mixing 7% of magnesium oxide (MgO) with iNbO ₃ ) is referred to as “cut angle, θ = 48.5 degrees: φ = 0.
It is cut at `` degree '', actually 10 (mm) × 10 (mm) × 20
(mm) An element having a nonlinear optical function having a rectangular parallelepiped shape.

The mirror 24 is an optical device that reflects the seed light output from the OPO 22 and projects the seed light to the dichroic mirror 34. The dichroic mirror 34 transmits the pump light and Reflects light,
An optical device having a function of guiding the light to the MLN 36 by matching the optical path of the seed light with the optical path of the pump light. further,
The dichroic mirror 38 is an optical device having a function of projecting unnecessary pump light to the non-reflector 42 that does not reflect the pump light, and transmitting the signal light and the idler light and guiding the light to the Ge element 44. The non-reflector 42 can be realized by a material such as a black felt cloth. Further, the Ge element 44 is an element for transmitting only idler light and outputting infrared light.

The timing generator 40 is a circuit for giving a trigger signal to an optical device in order to obtain two types of pulsed light as described above. For example, the timing generator 40 is implemented by various logic circuit elements, electronic elements such as resistors and capacitors. it can.

The adjusting mechanism 50 is realized by a rotating stage to which the MLN 36 is fixed, and operates the rotating stage so that the pump light and the seed light enter the MLN 36 at a desired phase matching angle. This is a component for adjusting the arrangement state of the MLN 36. Here, the phase matching angle is an angle measured from the optical axis of the nonlinear optical crystal in a direction in which the phase velocities of the pump light and the seed light coincide with each other.

Note that the phase matching angle is an angle that is set in advance when the infrared ray generating device is started. Since the set angle is related to the principle of the present invention, the principle will be described later. I will tell you when.

Hereinafter, the principle of the present invention will be described, and then specific operations will be described. FIG. 2 is a diagram illustrating the “dependence of the idler light (or signal light) wavelength on the phase matching angle” exhibited by the MLN 36. The horizontal axis is the adjustment mechanism 5
The phase matching angle of the MLN 36 which is adjusted by operating 0, and the vertical axis indicates the wavelength of idler light (or signal light) generated by the optical parametric amplification action of the MLN 36.

FIG. 2 shows three types of characteristics. Such characteristics are obtained by using TiS, which is a light source of pump light.
It is determined by the output wavelength of the laser 30 (variable between 750 and 850 (nm)).

Therefore, in FIG. 2, the pump light (TiS
The wavelength of the output light of the laser 30 is 750, 822, 84.
The graph shows the dependence of the idler light (or signal light) wavelength on the phase matching angle in the three types of 0 (nm).

FIG. 3 is a diagram showing only the dependence characteristic of the phase matching angle of the idler light (or signal light) wavelength when the wavelength of the pump light is 840 (nm) for explanation of the principle.

In FIG. 3, the horizontal axis is the phase matching angle of the MLN 36 adjusted by operating the adjusting mechanism 50, and the vertical axis is M
It shows the wavelength of idler light (or signal light) generated by the optical parametric amplification action of LN36.

Now, referring to FIG.
The phase matching angle initially set will be described. B in the figure
Is a dotted line for explaining the generation state of idler light and signal light when the phase matching angle is set to about 46.25 degrees. There are four intersections between the dotted line B and the characteristic curve, and they are referred to as point d, point c, point c ', and point d' in order of shorter wavelength.

The points d and d 'correspond to the point at which a pair of signal light d and idler light d' are generated.
The point c ′ corresponds to a point where a pair of signal light c and idler light c ′ is generated. When the phase matching angle is set such that four intersections are formed, two sets of idler light and signal light are generated.

At such a set angle, the change amount of the idler light (or signal light) wavelength with respect to the change amount of the phase matching angle is large, that is, the differential coefficient of the change of the phase matching angle with respect to the change of the divided frequency wavelength is large. At the set angle once set, the wavelength of the idler light (or signal light) cannot be changed in a wide range. In order to change the wavelength of the idler light (or signal light) in a wide range, it is necessary to determine an appropriate phase matching angle as needed and operate the adjusting mechanism 50 so that the phase matching angle becomes a set angle. Would.

This means that the phase matching angle changes by about 0.75 degrees with respect to the change in the wavelength of the idler light having a width of about 0.5 (μm), as can be seen from the area α in FIG. Therefore, it is difficult to change the wavelength of the idler light (or the signal light) in a wide range at the set angle once set.

Next, A in the figure indicates that the phase matching angle is about 45.
It is a dotted line for explaining the generation state of idler light and signal light when set to 75 degrees. There are two intersections between the dotted line A and the characteristic curve, and the point b having the shorter wavelength corresponds to the signal light, and the other intersection a corresponds to the point where the idler light is generated. When the phase matching angle is set such that two intersections are formed, a pair of idler light and signal light are generated.

With such a set angle, the change amount of the phase matching angle with respect to the change amount of the idler light (or signal light) wavelength is small, that is, the change of the phase matching angle with respect to the change of the idler light (or signal light) wavelength. The differential coefficient becomes “0”. Such a point is called a retracing point. Further, the phase matching angle with respect to the retracing point is called a retraced phase matching angle.

At the set angle corresponding to the retracing point, the wavelength of the idler light (or signal light) can be changed in a relatively wide range. Note the following about the retracing points.

The retracing point mathematically indicates a point (point) as shown in FIG. 3, but acts as an area having a certain width as an optical characteristic. That is, by changing the wavelength of the seed light (signal light) at the retracing point, the wavelength of the idler light can change within a predetermined range. This is known as an allowable range (acceptance range) of the characteristic curve.

Of course, the retracing phase matching angle may be obtained by treating the retracing point shown in FIG. 3 as a mathematical point. As a specific example, as can be seen from the region β in FIG. 3, even if the wavelength of the idler light is changed with a wavelength width of about 0.7 (μm), the phase matching angle is about 0 (μm).
The wavelength of the idler light (or the signal light) can be changed in a wide range at the set angle once set because it changes only 25 degrees. This means that the phase matching angle at which there is a point where the differential coefficient of the phase matching angle change with respect to the idler light (or signal light) wavelength change is “0” is set as the set angle, and the optical parametric amplification characteristics of the MLN are set. This is because a region in which the wavelength can be changed even when the phase matching angle does not change much is used.

The point e (when the phase matching angle is about 46.75)
), The differential coefficient of the phase matching angle change with respect to the idler light (or signal light) wavelength change is “0”, but the wavelengths of the idler light and the signal light coincide with each other. Since it is difficult to obtain infrared light of a wavelength, it is not generally used practically. Note that such a point e is called a digitizing point.

The longest wavelength of a seed light source which is relatively easily available at present is about 2.0 (μm), and in an optical experiment such as vibrational spectroscopy, an infrared ray generating apparatus of about 3.0 to 4.0 (μm) is used. Considering that the development of the MLN 36 is desired, using the MLN 36, the second optical system 110 for generating seed light, the first optical system 100 for generating pump light, and the like having the above-described characteristics, It is preferable to adopt an apparatus configuration as described in the present embodiment in which idler light is generated as infrared rays (about 3.0 (μm)) by optical parametric amplification of the MLN 36.

As described above, the present invention is characterized in that the adjusting mechanism 50 is operated so that the phase matching angle corresponding to the retracing point becomes the incident angle of the pump light to the MLN 36.

FIG. 4 is an explanatory diagram showing an example of the relationship between the wavelength of pump light, the wavelength of infrared light (the wavelength of idler light), and the retracing phase matching angle. The characteristics of the MLN used were, as described above, lithium niobate (l
A crystal obtained by mixing 7% of magnesium oxide (MgO) with iNbO ₃ ) was cut at a cut angle of 48.5 degrees.

4, the horizontal axis represents the wavelength of the pump light, the vertical axis on the left side of the drawing represents the infrared light wavelength, and the vertical axis on the right side of the drawing represents the retracing phase matching angle. Is shown. A in FIG. 4 indicates the relationship between the infrared light wavelength and the pump light wavelength. B in FIG. 4 shows the relationship between the retracing phase matching angle and the pump light wavelength.
It is shown that both the infrared light wavelength and the retracing phase matching angle decrease as the infrared light wavelength becomes longer.

The operation of generating infrared light will now be described assuming that the pump light has been adjusted so as to be incident on the MLN at a retracing phase matching angle. First,
The pulse light output from the TiS laser 30 is
2 and is emitted as pulse light having a repetition frequency of 10 (HZ), which becomes pump light (angular frequency ω1). Note that the timing generator 40 controls the operation of the optical amplifier so that the repetition frequency becomes 10 (HZ).

On the other hand, the pulse light output from the YAG laser 20 pulsating by the operation of the timing generator 40 is converted into near-infrared pulse light by optical parametric amplification in the OPO 22 and output.

The near-infrared light output from the OPO 22 acts as seed light, and its wavelength (angular frequency ω2)
Can be changed within a predetermined wavelength range by operating the operation dial provided in the OPO 22 described above.

Next, the seed light (angular frequency ω 2) generated by the second optical system 110 is reflected by the mirror 24 and enters the dichroic mirror 34. Meanwhile, the first
The pump light generated by the optical system 100 also enters the dichroic mirror 34.

The dichroic mirror 34 functions as an optical path aligning optical system for aligning the optical paths of both optical systems. Then, the seed light and the pump light enter the MLN 36 at a preset phase matching angle. At this time, idler light and signal light are amplified and output by the optical parametric amplification of the MLN 36, which is a nonlinear element.

At this time, according to the principle of the optical parametric amplification, the angular frequencies of the signal light and the idler light are respectively set to ω
2, ω3, “ω2> ω3, ω1 = ω2 + ω3
(However, ω1 is the angular frequency of the pump light) ”.

Next, the dichroic mirror 38 is
It reflects the pump light transmitted through the inside of N36, and transmits the signal light and the idler light. Since the pump light reflected by the dichroic mirror 38 is unnecessary light, the pump light is projected to the non-reflector 42 to eliminate the unnecessary light. As a result, the pump light disappears.

On the other hand, the Ge element 44 transmits only the idler light out of the signal light and the idler light, and outputs the transmitted idler light as infrared light. OPO
By changing the frequency .omega.2 of the seed light by operating the operation dial 22, the wavelength of the outputted infrared light is changed within a predetermined range.

Further, in the present apparatus, once the adjustment using the adjustment mechanism 50 is performed, it is necessary to perform the adjustment operation using the adjustment mechanism 50 unless the optical device such as the TiS laser 30 is changed. Absent.

FIG. 5 shows an output characteristic example of an infrared output device constituted by an optical device having the above-mentioned characteristics. T
The wavelength of the iS laser 30 is 778 (nm), and the retracing phase matching angle for this is 46.06 degrees.

The horizontal axis in FIG. 5 shows the wavelength of seed light (signal light) and the wavelength of infrared light generated as idler light, and the vertical axis shows the intensity of infrared light (arbitrary unit). . FIG.
The measurement results are obtained in such a manner that the phase matching angle of the pump light incident on the MLN approaches the retracing phase matching angle in the order of a, b, c, and d. The infrared intensity was measured with an infrared detector such as a laser power meter (pyroelectric photodetector) having sensitivity to light in the infrared region.

In FIG. 5A, two peaks are generated because two types of idler light are generated as shown in FIG. 3B. As can be seen from the characteristic curve in FIG. 3, as the phase matching angle of the pump light incident on the MLN approaches the retracing phase matching angle, the two peak positions generated by the generation of the idler light approach. Then, through the state shown in FIG.
Has a single peak intensity distribution because the idler light becomes one.

As can be seen from FIG. 5D, when the phase matching angle of the pump light incident on the MLN becomes the retracing phase matching angle, the pump light is in the infrared region of 3.4 to 3.8 (μm). , And high output infrared rays can be obtained.

FIG. 5C is an example of the output in the process in which the number of peaks generated by the generation of the idler light changes from two to one, and thus is slightly smaller than the retracing phase matching angle (in FIG. 5, When the phase matching angle is set so as to be 0.02 degrees, infrared output characteristics having flat characteristics over a wide wavelength range can be obtained.
In FIG. 5c, infrared light having a flat output characteristic in a wavelength range of about 3.35 to 3.85 (μm) was obtained.

As described above, the light output from the TiS laser 30 is used as pump light, the light output from the YAG laser 20 is used as seed light, and idler light is output as infrared light using MLN optical parametric amplification. Approximately 3 (μ
m) It is possible to realize an infrared ray generator that can change the wavelength within a predetermined range of about m).

Although the apparatus configuration for obtaining pulse light has been described according to the above-described embodiment, FIG.
By slightly changing the device configuration shown in (1), it is possible to realize a CW infrared ray generating device that generates CW infrared rays.

In this case, each of the first optical system and the second optical system is replaced with a first light source and a second light source capable of CW oscillation, and an unnecessary timing generator 40 is removed.

More specifically, for example, the first light source is configured using a TiS laser that oscillates CW, and the second light source is a tunable OPO 22 that uses laser light of a YAG laser that oscillates CW as pump light. It is configured using. Note that OP
By setting the wavelength variable range of O22 to include a longer wavelength region than the wavelength of the pump light output from the first light source, optical parametric amplification can be performed.
Further, the second light source may be constituted by one wavelength-variable laser device without using the OPO 22.

Then, the arrangement of the mirror 24 and the dichroic mirror 34 is adjusted to superimpose the lights output from the two light sources, and the apparatus is configured to be able to irradiate the MLN 36 with the superimposed light. The adjusting mechanism 50 and the dichroic mirror 38
The Ge element 44 may have the same configuration as that of the pulse type device. Further, in order to improve the efficiency of optical parametric amplification, the MLN 36
May be included in the resonator.

The retracing phase matching angle set by the adjusting mechanism 50 is the same as that of the pulse type device. With such a device configuration, it is also possible to realize a CW infrared ray generating device.

In the above-described embodiment, the non-linear
The case where MLN is adopted as the optical element
But other nonlinear optical elements such as LiB_ThreeO_Five, KTP, LiO_Three, A
sGaS _2,AsGaSe_TwoEtc. may be used.

Since the pulse width of the outputted infrared light is substantially equal to the pulse width of the pump light, the infrared light having the picosecond or femtosecond pulse width is obtained by setting the pulse width of the pump light to picosecond or femtosecond. With such a configuration, as the second light source, a nanosecond pulse light source or a light source capable of CW oscillation (such as a semiconductor laser) described in the present embodiment is used.
Can be used to realize devices used for various optical experiments. Further, the present apparatus itself may be used as a seed light source of another narrow band laser. (Experimental example) An optical experiment was performed using an apparatus including an optical device having the above-described characteristics.

More specifically, an experiment for measuring an SF signal, which is a sum frequency signal generated by the LB film when irradiated with light, was performed using this apparatus. In order to carry out this experiment, infrared light output from an infrared light generating device having an optical device having the characteristics described in the above embodiment and infrared light extracted by an optical system such as a beam splitter not shown in FIG. The LB film was irradiated with the laser light of the TiS laser 30. Note that the intensity of the SF signal was detected by a photomultiplier.

It is to be noted that sum frequency generation, which is a phenomenon in which a laser beam is irradiated on a specific material to generate light having the sum frequency of both lights, is generally known. The LB film to be measured is obtained by growing arachiic acid ((CH ₃ (CH ₂ ) ₁₈ COO) ₂ Cd) having a thickness of about 10 (nm) on a slide glass.

The incident angle of the infrared ray to the LB film is 40 degrees, and the incident angle of the TiS laser beam to the LB film is 4 degrees.
The experiment was performed at 5 degrees. The irradiation of both laser beams to the LB film was performed in a so-called parallel type.

FIG. 6 shows the experimental results. The horizontal axis in FIG. 6 is a value expressing the wavelength of infrared rays as a wave number, and the vertical axis is a value indicating the strength of the SF signal when an appropriate magnitude of the intensity signal is “1”. Plotted.

By operating the operation dial of the OPO 22 to change the wave number of infrared rays (corresponding to the reciprocal of the wavelength),
As a result of measuring the strength of the SF signal, about 2950 (1 / c
In m), the characteristic that the SF signal has a peak value was obtained.
This peak is presumed to be due to vibration of the “CH ₃ ” molecule.

As described above, according to the present apparatus, 3 to 4 (μ
m) Various optical experiments can be performed using infrared rays. As described above, according to the present invention, when infrared light is generated using the optical parametric effect, the number of optical devices requiring position adjustment such as a nonlinear optical element and a grating is reduced, and adjustment man-hours are reduced. It can be reduced.

Further, a wide infrared wavelength range, particularly, 3.35
This makes it possible to realize a device that generates high-output infrared light of up to 3.85 (μm) without rotating the crystal.

[0081]

As described above, according to the first or second aspect of the present invention, it is possible to reduce the number of optical devices that need to be adjusted in position, such as a nonlinear optical element and a grating.
An infrared light generator that can reduce the number of adjustment steps can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a phase matching angle and an idler light (or signal light) wavelength.

FIG. 3 is an explanatory diagram showing a phase matching angle to be set by an adjustment mechanism.

FIG. 4 is an explanatory diagram showing a relationship between a pump light wavelength, an infrared light wavelength, and a retracing phase matching angle.

FIG. 5 is an explanatory diagram of an infrared output characteristic of the present device.

FIG. 6 is an explanatory diagram of an optical experiment result using the present apparatus.

FIG. 7 is a configuration diagram of a conventional device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 lens 2 condenser lens 3 condenser lens 4 grating 5 mirror 6 beam splitter 7 delay prism 8 mirror 9 dichroic mirror 10 slit 11 MLN 2 12 pump laser 15 OPA section 17 pump light generation section 19 seed light generation section 20 YAG laser 22 OPO 24 Mirror 30 TiS laser 32 Optical amplifier 36 MLN 38 Dichroic mirror 40 Timing generator 42 Non-reflector 44 Ge element 50 Adjustment mechanism

Claims (2)

[Claims] 1. An apparatus for generating infrared light using optical parametric amplification, comprising: a first optical system for outputting light with a predetermined period of pulses; and a light longer than the light within a predetermined wavelength range. A second optical system that outputs a pulse of light of the selected wavelength in synchronization with the pulse, an optical path alignment optical system that aligns the optical paths of both optical systems, and an output from the optical path alignment optical system. A function of receiving light, performing output parametric amplification using output light of the first optical system as pump light, and output light of the second optical system as seed light, and outputting infrared light as idler light. In the dependence characteristic of the phase matching angle of the idler light (or signal light) wavelength exhibited by the nonlinear optical element and the nonlinear optical element determined by the wavelength of the light of the first optical system, the idler light having the phase matching angle change ( Or signa Light) for adjusting the arrangement state of the nonlinear optical element so that the pump light is incident on the nonlinear optical element at a phase matching angle at which two points at which the differential coefficient with respect to the wavelength change becomes zero occur. An infrared light generator including an adjustment mechanism. 2. An apparatus for generating infrared light using optical parametric amplification, comprising: a first light source for outputting light; and a light having a longer wavelength than the light output from the first light source. A second light source that is selectable within a range and outputs light of the selected wavelength, an optical path alignment optical system that performs optical path alignment of both light sources, and receives light output from the optical path alignment optical system, A nonlinear optical element having a function of performing optical parametric amplification using output light of the first light source as pump light and output light of the second light source as seed light, and outputting infrared light as idler light; In the dependence characteristic of the phase matching angle of the idler light (or signal light) wavelength exhibited by the nonlinear optical element determined by the wavelength of the light source, the differential coefficient of the phase matching angle change with respect to the idler light (or signal light) wavelength change is zero. What In the phase matching angle point occurs two points, as the pump light to the nonlinear optical element is incident, infrared light generating device and an adjustment mechanism for adjusting the arrangement of the non-linear optical element.