JP4534027B1 - Electromagnetic wavefront shaping element, electromagnetic wave imaging apparatus including the same, and electromagnetic wave imaging method - Google Patents

Abstract

An electromagnetic wavefront shaping element for performing imaging with electromagnetic waves at high speed, an electromagnetic wave imaging device including the same, and an electromagnetic wave imaging method are provided.
An electromagnetic wavefront shaping element (1) for shaping a wavefront of an electromagnetic wave (10), a semiconductor (23), an insulator (22) formed on the semiconductor (23), and an array on the insulator (22). A plurality of electrodes 21 to be formed; and a voltage applying means 3 for applying a predetermined applied voltage between each of the plurality of electrodes 21 and the semiconductor 23 and controlling the applied voltage. When the pulse laser beam 9 is incident on the semiconductor 23, the applied voltage is controlled by the voltage applying means 3, so that the pulse laser of the semiconductor 23 corresponding to the electrode 21 to which the applied voltage is applied. The radiation intensity of the electromagnetic wave 10 generated from the light incident surface 23a is controlled.
[Selection] Figure 1

Description

  The present invention relates to an electromagnetic wave wavefront shaping element for radiating an electromagnetic wave while controlling an electromagnetic wavefront, an electromagnetic wave imaging apparatus including the same, and a technique of an electromagnetic wave imaging method.

  With the rapid development of technology using the terahertz (THz) frequency band, technological development applying terahertz waves to various industrial fields is progressing, and at the same time, demand for various THz components is expanding. For example, using the excellent permeability of terahertz waves, luggage inspection devices used in security checks at airports, etc. and terahertz waves (terahertz light) are applied to spectroscopic measurements for the identification of substances and drug / food inspections. Development of applications such as use is expected. Further, as such a technique, there is an imaging apparatus using a terahertz wave disclosed in Non-Patent Document 1, and in such an imaging apparatus, a mask is used for wavefront shaping (modulation) of the generated terahertz wave. (Metal mesh hole filter: a filter in which holes are formed in a metal plate. See FIG. 15) is generally used.

  In addition, the imaging apparatus described in Non-Patent Document 1 can acquire a spatial distribution and spectral characteristics of a substance contained in a sample at a time as a map by irradiating the sample with a terahertz wave modulated by the mask. It is. That is, in such an imaging apparatus using terahertz waves, non-destructive inspection of a sample is possible.For example, a terahertz wave is irradiated on a package whose contents are unknown as the sample, and the package is removed. By analyzing the transmitted terahertz wave, it is possible to acquire the spectral characteristics and physical shape of the chemical component of the contents as a map or an image.

  On the other hand, Patent Document 1 describes an electromagnetic wave modulation device as a technique using a terahertz wave. This electromagnetic wave modulation device forms a spatial electron density distribution in which the electron density of plasma changes in at least one direction within the wavefront in a radio wave path including a surface that receives the wavefront of the electromagnetic wave (terahertz wave), thereby propagating the electromagnetic wave. The state (propagation direction) is changed. In addition, the electromagnetic wave modulation device includes generating means for generating plasma and electron density distribution adjusting means for adjusting the spatial electron density distribution of the plasma. Specifically, the electromagnetic wave modulation device described in Patent Document 1 applies a terahertz wave emitted from a terahertz wave light source to a fixed target object as described in Example 7 (FIG. 12 in Patent Document 1). Condensing and deflecting (scanning) the direction of the condensed beam from right to left to perform imaging with terahertz waves.

JP 2008-151619 A

Y. C. Shen et al., APPLIED PHYSICS LETTERS 95, 231112 (2009)

  However, in the imaging apparatus described in Non-Patent Document 1, when a terahertz wave is emitted to a sample, it is necessary to mechanically replace the mask in order to obtain a different wavefront (modulation) pattern. Therefore, there is a problem that the measurement speed by imaging is lowered.

  In addition, the electromagnetic wave modulation device described in Patent Document 1 requires a terahertz wave itself used for scanning to be generated by another device, so that the device configuration becomes complicated. Furthermore, in the electromagnetic wave modulation device described in Patent Document 1, it is considered that the terahertz wave is attenuated because it is deflected by passing the terahertz emitted from the terahertz wave light source through the modulation device. As a result, the emission efficiency is deteriorated.

  In other words, since the imaging apparatus described in Non-Patent Document 1 involves a time delay due to mechanical operation, security of luggage carried out at a medical site where a detection result is required in real time or in transportation, etc. Not enough to apply to the check. In addition, as in Patent Document 1, it is a problem whether terahertz wave deflecting means and terahertz wave light source are not separately configured, but can be configured together as one element or device.

  Accordingly, the present invention has been made to solve the above-described problems, and provides an electromagnetic wavefront shaping element, an electromagnetic wave imaging apparatus including the same, and an electromagnetic wave imaging method for performing imaging with electromagnetic waves at high speed. Objective.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in claim 1,
An electromagnetic wavefront shaping element for performing wavefront shaping on an electromagnetic wave,
Semiconductors,
An insulator formed on the semiconductor;
A plurality of electrodes formed in an array on the insulator;
A voltage applying means for applying a predetermined applied voltage between each of the plurality of electrodes and the semiconductor, and for controlling the applied voltage, respectively;
When pulsed laser light is incident on the semiconductor, the applied voltage is controlled by the voltage applying means, so that an electromagnetic wave generated from the pulsed laser light incident surface of the semiconductor corresponding to the electrode to which the applied voltage is applied. It is an electromagnetic wavefront shaping element for controlling the radiation intensity.

In claim 2,
An electromagnetic wave imaging apparatus comprising the electromagnetic wave wave shaping element according to claim 1,
Means for irradiating the pulse laser beam incident surface of the semiconductor with the pulse laser beam;
An electromagnetic wave imaging apparatus comprising: means for radiating an electromagnetic wave generated from an incident surface of the semiconductor pulse laser beam to an inspection object and detecting the electromagnetic wave transmitted or reflected by the inspection object.

In claim 3,
An electromagnetic wave imaging method applied to an electromagnetic wave imaging device comprising the electromagnetic wave wavefront shaping element according to claim 2,
An irradiation step of irradiating the pulse laser beam incident surface of the semiconductor with the pulse laser beam;
An electromagnetic wave radiation step of radiating an electromagnetic wave generated from the incident surface of the semiconductor pulsed laser light to the inspection object;
When pulsed laser light is incident on the semiconductor, the applied voltage is controlled by the voltage applying means, so that an electromagnetic wave generated from the pulsed laser light incident surface of the semiconductor corresponding to the electrode to which the applied voltage is applied. An electromagnetic wave control process for controlling the radiation intensity of
And an electromagnetic wave detecting step of detecting an electromagnetic wave transmitted or reflected by the inspection object.

In claim 4,
The electromagnetic wave imaging method further includes an image processing step of performing image processing based on the electromagnetic wave detected by the electromagnetic wave detection step.

In claim 5,
An electromagnetic wavefront shaping element for performing wavefront shaping on an electromagnetic wave,
Semiconductors,
An insulator formed on the semiconductor;
A plurality of electrodes formed in an array on the insulator;
A voltage applying means for applying a predetermined applied voltage between each of the plurality of electrodes and the semiconductor, and for controlling the applied voltage, respectively;
When pulsed laser light is incident on the semiconductor, the applied voltage is controlled by the voltage applying means, so that an electromagnetic wave generated from the pulsed laser light incident surface of the semiconductor corresponding to the electrode to which the applied voltage is applied. It is an electromagnetic wave wave front shaping element which deflects the radiation direction of.

In claim 6,
The voltage applying means includes
The semiconductor corresponding to the electrode on which the predetermined pattern is formed by controlling ON or OFF of the applied voltage to the plurality of electrodes, and forming a predetermined pattern made of the electrodes to which the applied voltage is applied. This is an electromagnetic wavefront shaping element that deflects the radiation direction of the electromagnetic wave generated from the incident surface of the pulse laser beam.

In claim 7,
An electromagnetic wave imaging apparatus comprising the electromagnetic wave wavefront shaping element according to claim 5 or 6,
Means for irradiating the pulse laser beam incident surface of the semiconductor with the pulse laser beam;
The electromagnetic wave generated from the semiconductor laser beam incident surface is radiated to the inspection object, and the inspection object is scanned by deflecting the radiation direction of the generated electromagnetic wave, and the electromagnetic wave transmitted or reflected by the inspection object. And means for detecting electromagnetic waves.

In claim 8,
An electromagnetic wave imaging method applied to an electromagnetic wave imaging device comprising the electromagnetic wave wavefront shaping element according to claim 7,
An irradiation step of irradiating the pulse laser beam incident surface of the semiconductor with the pulse laser beam;
An electromagnetic wave radiation step of radiating an electromagnetic wave generated from the incident surface of the semiconductor pulsed laser light to the inspection object;
When pulsed laser light is incident on the semiconductor, the applied voltage is controlled by the voltage applying means, so that an electromagnetic wave generated from the pulsed laser light incident surface of the semiconductor corresponding to the electrode to which the applied voltage is applied. An electromagnetic wave scanning step of deflecting the radiation direction of the object and scanning the inspection object;
An electromagnetic wave detection method for detecting an electromagnetic wave transmitted or reflected by the inspection object.

In claim 9,
An electromagnetic wave imaging method further comprising an image processing step of performing image processing based on the electromagnetic wave detected by the electromagnetic wave detection step.

  As effects of the present invention, the following effects can be obtained.

  Since the elements themselves are arrayed and wavefront shaping can be performed while generating electromagnetic waves, there is no need to pass through a wavefront shaping filter. In addition, since it is possible to electrically control the radiation intensity and radiation direction of the generated electromagnetic wave, it is possible to scan the inspection object while performing wavefront shaping in real time, dramatically increasing the electromagnetic wave visualization speed. Can be improved.

1 is a schematic diagram of an electromagnetic wave imaging apparatus provided with an electromagnetic wave front shaping element according to the present invention. The A arrow directional view of the electromagnetic wave wave front shaping element in FIG. The side schematic diagram. The schematic diagram of the energy band distribution of the electromagnetic wave wave front shaping element which concerns on this invention. Explanatory drawing for demonstrating the principle of electromagnetic wave intensity control. The figure which shows the flow of the electromagnetic wave imaging method. It is a figure which shows the result of the experiment which controls a terahertz wave radiation intensity, (a) is a figure which shows an applied voltage pattern, The left figure of (b) is a figure which shows the imaging when an applied voltage is 10V, The right of (b) The figure shows imaging in which the applied voltage is different from 10V to 0V. The figure which shows the relationship between terahertz wave intensity and an applied voltage. The figure which shows another Example of an electromagnetic wave imaging device. The figure which shows another Example of an electromagnetic wave imaging device. It is explanatory drawing explaining the control method of the radiation | emission direction of a terahertz wave, (a) is a figure which shows the case where an application electrode is a horizontally long type, (b) is a figure which shows the case where an application electrode is a vertically long type. Explanatory drawing explaining simulation conditions. The figure which shows a simulation result. The figure which shows a simulation result. The schematic diagram which shows the conventional mask.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the part which is common in each figure, and the overlapping description is abbreviate | omitted.

FIG. 1 shows an embodiment of an electromagnetic wave imaging apparatus provided with an electromagnetic wave front shaping element of the present invention.
The electromagnetic wave imaging device 20 radiates a pulse electromagnetic wave 10 to the inspection object 30 and analyzes the pulse electromagnetic wave 10 transmitted or reflected through the inspection object 30 to perform nondestructive inspection / measurement of the inspection object 30. For example, it is possible to acquire (imaging) spectral characteristics, physical shapes, and the like of chemical components of contents included in the inspection object 30 as a map or an image. The electromagnetic wave imaging device 20 includes an electromagnetic wave front shaping element 1, an irradiation device (optical system), a detection / conversion device 4, a control / analysis device 8, and the like. The details of the apparatus configuration and the measurement principle will be described below.

The electromagnetic wavefront shaping element 1 is an element for performing wavefront shaping on the pulsed electromagnetic wave 10 and has a square shape (15 mm × 15 mm in this embodiment) as shown in FIG. The electromagnetic wave wave shaping device 1 mainly includes an electrode 21, an insulator 22, a semiconductor 23, a transparent substrate 24, and a voltage applying means 3 (see FIG. 1). That is, the electromagnetic wave wave front shaping element 1 is formed so as to abut on the insulator 22, one end surface (the right end surface in FIG. 3) of the insulator 22, the semiconductor 23 having a predetermined thickness, and the semiconductor 23. A transparent substrate 24 formed so as to contact one end face (right end face in FIG. 3), an electrode 21 formed so as to contact the other end face (left end face in FIG. 3) of the insulator 22, Have The electromagnetic wavefront shaping element 1 emits a pulsed electromagnetic wave 10 when the pulsed laser light 9 is incident on the incident surface 23a, which is one end face of the semiconductor 23 included in the electromagnetic wavefront shaping element 1, via the transparent substrate 24. Is. As a method for producing the electromagnetic wave wave front shaping element 1, first, a thin film is formed (film thickness: 150 nm) by vapor deposition of the semiconductor 23 (Si in this embodiment) on the transparent substrate 24 (film thickness: 600 μm). An insulator 22 (in this embodiment, SiO ₂ ) is formed on the semiconductor 23 by thermal oxidation or vapor deposition (film thickness: 275 nm), and an electrode 21 (in this embodiment, in this embodiment) is formed. , Au) is formed by forming a thin film in an array by vapor deposition (film thickness: 200 nm). That is, by stacking a semiconductor 23 (Si), an insulator 22 (SiO ₂ ), and an electrode 21 (Au) that is a metal part (Metal part) in this order on a transparent substrate 24 that is a plate-like thin film, a so-called MOS structure chip is formed. It is composed.

Further, in this embodiment, silicon oxide (SiO ₂ ) is used as the insulator 22, but silicon nitride or the like can be used instead. The insulator 22 has a thickness of about 275 nanometers, and the semiconductor 23 has a thickness of about 150 nanometers. The semiconductor 23 has a thickness of pulse laser light 9 in order to obtain a large amplitude intensity of the pulse electromagnetic wave 10. It is desirable that the size be equal to the light penetration length determined by the wavelength of the light and the type of the semiconductor 23. The light penetration length is the reciprocal of the light absorption coefficient for the semiconductor 23. For example, when the wavelength of the pulse laser beam 9 is 790 nanometers and the type of the semiconductor 23 is high resistance silicon, the thickness of the semiconductor 23 is about 2 microns, so that the pulse electromagnetic wave 10 can be generated efficiently. Can be made.

  As shown in FIGS. 2 and 3, the electrode 21 is a plurality of metals (a metal that can be energized, which uses an Au thin film in the present embodiment) formed in an array on the insulator 22. The electrode 21 is composed of a total of 16 electrodes, the number of electrodes being 4 rows x 4 columns. The electrodes 21, 21,... Are partitioned at predetermined intervals, and Al bonding (not shown) is applied to each end of the electrodes 21, 21,. The voltage applying means 3 (see FIG. 1) is interposed between the wirings connected via Ag paste coated on the outside of the Si film substrate 23.

The voltage applying means 3 applies a predetermined applied voltage between each of the plurality of electrodes 21 and the semiconductor 23 and controls the applied voltage.
That is, the voltage applying means 3 can apply a predetermined voltage to each of the electrodes 21, 21,... (Control the bias), and the electrodes 21, 21,. A voltage can be applied between the semiconductor 23 and the semiconductor 23. This makes it possible to control the width of the depletion layer in the semiconductor 23 immediately below the electrodes 21, 21,.
The number, shape, and arrangement pattern of the electrodes are not particularly limited to the present embodiment, and may be appropriately changed depending on the composition, shape, size, etc. of the inspection object.
Here, as shown in FIG. 2, the arrangement numbers in the horizontal direction of the electrodes 21, 21,... Are 1 to 4, and the arrangement symbols in the vertical direction are defined as A to D for convenience.

  The transparent substrate 24 is a holding member for holding the electrodes 21, 21,..., The insulator 22 and the semiconductor 23. The semiconductor 23, the insulator 22, and the electrodes 21, 21,. Necessary when producing. Furthermore, it is necessary to maintain the mechanical strength of the electromagnetic wave wave shaping element 1. In this embodiment, sapphire is used as the transparent substrate 24.

  Here, the principle of generation of electromagnetic waves by laser pulse irradiation will be described. When a laser beam having energy larger than the band gap is irradiated to a place where an electric field E exists in a semiconductor, an electron / hole pair is generated by photoexcitation, and the electron / hole pair is accelerated by the electric field E. Current is generated. When the laser beam is continuous light, a steady current flows, but when the laser beam is pulsed light, the excited electron-hole pairs relax in a certain time, and the current stops flowing. Depending on the width of the light pulse and the relaxation time, a pulsed current flows. According to the following equation (1) derived from the Maxwell equation of classical electromagnetism, when a time change occurs in the current flowing through the semiconductor, electromagnetic waves are emitted from the semiconductor.

In the above equation (1), E _emission is the electric field vector of the electromagnetic wave, J is the photocurrent density vector, n is the density of the photoexcited electron / hole pair, e is the elementary charge amount, and v is the light The drift velocity μ of the electron-hole pair accelerated by the electric field E _local in the semiconductor at the irradiated position is the charge mobility.

As can be seen from the equation (1), the amplitude intensity of the generated electromagnetic wave is proportional to the electric field E _local in the semiconductor at the position irradiated with light.

  FIG. 4 is a schematic diagram of the energy band distribution of the electromagnetic wave wave front shaping element 1, where the horizontal axis indicates the position and the vertical axis indicates the energy. Moreover, EC in the figure is a conduction band, and EV is a valence band. A depletion layer is formed at the boundary between the insulator 22 and the semiconductor 23. The depletion layer is a region where no carrier exists, and a local electric field E is formed in the depletion layer. Accordingly, an electric field constantly exists in the depletion layer without applying a voltage from the outside. When this depletion layer is irradiated with light to generate electron / hole pairs, electromagnetic waves are generated according to the equation (1).

  Here, the direction and magnitude of the local electric field E may vary depending on the state of the boundary between the insulator 22 and the semiconductor 23 and the characteristics of the semiconductor 23. However, a particularly important point in the principle of electromagnetic wave generation is that a local electric field E is formed.

Further, in the present embodiment, the electric field E _local is controlled by applying a predetermined applied voltage to the electrode 21 by the voltage applying means 3, and the vibration of the electromagnetic wave generated by the control of the electric field E _local is performed. The intensity (radiation intensity) can be controlled.
That is, the principle of electromagnetic wave intensity control by the electromagnetic wave wavefront shaping element 1 having the MOS structure of this embodiment will be described in order with reference to FIG. 5. 1) Between the metal-Si (electrode 21-semiconductor 23) by the voltage applying means 3. A bias voltage is applied (the work function of the metal film changes), 2) the electric field of the depletion layer in the semiconductor 23 (Si layer) changes, 3) the instantaneous current changes, 4) the generated electromagnetic wave (terahertz wave) It is possible to control the radiation intensity of electromagnetic waves according to the flow that the electric field strength also changes.

The irradiation device (optical system) is means for irradiating the pulse laser light incident surface 23a of the semiconductor 23 of the electromagnetic wave wavefront shaping element 1 with the pulse laser light 9, and includes the pulse laser light source 2, the beam splitter 14, and the time delay means 15. The optical chopper 16 is mainly composed of a plurality of mirrors. The irradiation device (optical system) mainly has a function of irradiating the semiconductor 23 of the electromagnetic wave wavefront shaping element 1 with pulsed laser light 9 having a predetermined wavelength.
Note that the configuration of the mirror and the like used to change the direction of the pulse laser beam 9 is not limited to the present embodiment. Considering the arrangement of each component, for example, the number of mirrors may be increased as appropriate. You can change the configuration.

  Further, as shown in FIG. 1, in this embodiment, the plane formed by the path of the pulse laser beam 9 and the pulse electromagnetic wave 10 is substantially horizontal, that is, FIG. 1 is a top view configuration, and this configuration is viewed from the side. In addition, the pulse laser beam 9 and the pulse electromagnetic wave 10 are arranged so as to form a substantially horizontal plane. However, it is desirable to set appropriately according to the shape and fixing method of each device, and it is not necessary to configure the substantially horizontal plane.

  The pulse laser light source 2 is means for irradiating the pulse laser light 9. The pulse laser light source 2 irradiates the electromagnetic wave wavefront shaping element 1 with the pulsed laser light 9 on the laser light incident surface 23a of the semiconductor 23, thereby depending on the amount of voltage applied to the electrode 21 immediately above the irradiation position. This is a means for generating a pulsed electromagnetic wave 10 having an amplitude intensity. In addition, as the pulse laser light source 2 in this embodiment, a femtosecond titanium sapphire laser (repetition frequency 82 MHz, output 890 MHz, center wavelength 780 nm, pulse width 100 fs) is used.

Further, the pulse laser light source 2 may be a mode-locked titanium sapphire laser or a femtosecond fiber laser capable of generating the pulse laser light 9 as in this embodiment.
The wavelength of the pulse laser beam 9 is included in the range of 300 nanometers (300 nm = 0.3 μm) or more and 2 microns (2 μm) or less, and the time average energy is 0.1 mW or more and 10 W or less. The pulse width is preferably 1 femtosecond (1 fs = 0.001 ps) or more and 10 picoseconds (10 ps) or less.
That is, when exciting the electromagnetic wave, the electromagnetic wave can be excited without significantly affecting the semiconductor 23 by using the pulse laser light 9 having a small time width as a light source. In particular, by using femtosecond laser light as the pulse laser light 9, time-resolved measurement with high time resolution becomes possible, and the inspection object 30 can be observed in real time. Note that the maximum optical pulse width that does not affect the semiconductor 23 thermally can be estimated to be about 10 picoseconds. In addition, the use of a femtosecond laser has the effect of minimizing the adverse effects of heating by the laser.

  Further, as shown in FIG. 3, the pulsed laser light 9 is irradiated from the opposite side of the surface (the upper surface of the insulator 22) on which the electrodes 21, 21, ... of the electromagnetic wave wavefront shaping element 1 are formed. Is. In other words, the pulse laser beam 9 is emitted from the semiconductor 23 corresponding to the electrodes 21, 21,..., That is, the entire incident surface 23 a of the electrodes 21, 21,. It is irradiated over the range. For this purpose, as the semiconductor provided in the electromagnetic wave wavefront shaping element 1, a semiconductor film (semiconductor 23) produced on an insulator substrate (transparent substrate 24) that transmits the pulse laser beam 9 is used.

  The beam splitter 14 is a means for dividing the incident pulse laser light 9 into the probe light L1 and the pump light L2, and in this embodiment, the probe light L1 can be divided in the vertical direction with respect to the pump light L2 traveling straight. A half mirror is used. The probe light L1 is light used to acquire synchronization during the inspection of the inspection object 30, and the detection / conversion device passes from the beam splitter 14 via the mirror, the time delay means 15, the mirror, and the lens 35. 4 (detection element 19 described later) is irradiated. Further, the pump light L2 is applied to the incident surface 23a of the semiconductor 23 from the beam splitter 14 through the optical chopper 16 and the mirror.

  The incident angle of the pump light L2 on the incident surface 23a of the semiconductor 23 is preferably an angle at which the wavelength of the pulse laser light 9 (pump light L2) is most absorbed by the semiconductor 23 of the electromagnetic wave wave shaping device 1. . However, depending on the shape and fixing method of each device, it is not necessary to limit to this angle, and there is no particular limitation.

The time delay means 15 is a means arranged in the optical path of the probe light L1 and capable of periodically delaying the time when the amplitude intensity is detected by the detection / conversion device 4. The time delay means 15 includes a movable mirror 15a that can be periodically moved in a predetermined direction by a driving means (not shown), and a stage 15b that holds the movable mirror 15a. The time delay unit 15 can reflect the probe light L1 incident on the time delay unit 15 in a direction parallel to and opposite to the incident direction of the probe light L1. Thus, the time delay means 15 adjusts the optical path length of the probe light L1 by optically delaying the movable mirror 15a by reciprocating the movable mirror 15a in parallel and periodically with respect to the incident direction of the probe light L1. It is possible. The driving means is controlled by the control / analysis device 8.
That is, the time delay means 15 periodically detects the probe light L1 provided with a time delay amount at a predetermined time interval by moving the movable mirror 15a for adjusting the optical path length of the probe light L1. 4 (detection element 19 to be described later).

  The optical chopper 16 is disposed in the optical path of the pump light L2, and can chop the pump light L2 at a predetermined frequency.

  The detection / conversion device 4 radiates the pulse electromagnetic wave 10 generated from the incident surface 23a of the semiconductor 23 to the inspection object 30, and measures (detects) the amplitude intensity of the pulse electromagnetic wave 10 transmitted or reflected by the inspection object 30. ). The detection / conversion device 4 includes a detection element 19 that is an electromagnetic wave detection unit, a condensing unit 18, and a conversion unit. The detection / conversion device 4 condenses the pulse electromagnetic wave 10 transmitted or reflected by the inspection object 30 by the condensing means 18, detects the collected pulse electromagnetic wave 10, and detects the electric field amplitude of the pulse electromagnetic wave 10. This is converted into a time-varying voltage signal corresponding to the time waveform.

  The detection element 19 is, for example, a photoconductive antenna or the like, and is arranged so that the pulse electromagnetic wave 10 generated from the irradiation position of the pump light L2 on the incident surface 23a of the semiconductor 23 can enter, and in synchronization with the incidence of the pulse electromagnetic wave 10, the probe 19 When the light L1 is irradiated to a predetermined position of the detection element 19, a current proportional to the electric field strength (amplitude strength) of the pulse electromagnetic wave 10 incident upon the irradiation is generated.

  The condensing means 18 is a pair of off-axis parabolic mirrors, and the inspection object 30 is disposed between the parabolic mirrors, and is emitted from the incident surface 23 a of the semiconductor 23 with respect to the inspection object 30. In addition to condensing and radiating the pulsed electromagnetic wave 10, the pulsed electromagnetic wave 10 transmitted or reflected by the inspection object 30 is condensed and applied to one end of the detection element 19.

  The conversion means includes a current amplifier 27 connected to the detection element 19 and a lock-in amplifier 28 connected to the current amplifier 27. The lock-in amplifier 28 is connected to the optical chopper 16. In this conversion means, by measuring the current generated in the detection element 19, it is possible to detect the amplitude intensity of the pulsed electromagnetic wave 10a incident when the probe light L1 is applied to the detection element 19. Further, the frequency component included in the pulse electromagnetic wave 10 is included in a range from 10 gigahertz to 100 terahertz, so that the detection / conversion device 4 having a general configuration can be used. Further, the terahertz region is preferable to the gigahertz region as the pulsed electromagnetic wave 10 to be used in configuring the electromagnetic wave imaging apparatus 20 according to the present invention. When using the terahertz region, unlike using the gigahertz region, the electromagnetic wave can be easily guided to the detector by an optical technique using a mirror, a lens, or the like. On the other hand, the high-frequency region is more so-called light than the terahertz region. However, when using light, it is necessary to provide a means for distinguishing ambient light from signal light. It is preferable to use electromagnetic waves in the terahertz region rather than electromagnetic waves having a higher frequency than in the terahertz region.

The control / analysis device 8 measures the inspection object 30 qualitatively or quantitatively based on the amplitude intensity, for example, the spectral characteristics or physical shape of the chemical components of the contents contained in the inspection object 30. Can be acquired as a map or an image, and an analysis result can be displayed as an image (imaging).
That is, the control / analysis device 8 detects the presence / absence of the content (subject to be detected) contained in the inspection object 30 from the voltage signal converted by the conversion means of the detection / conversion device 4 (qualitative measurement). Analysis processing such as quantitative measurement of contents, specification of substances by spectroscopic measurement of contents, and predetermined analysis using a time-series waveform of the amplitude intensity (voltage value) of the detected pulsed electromagnetic wave 10, the analysis It is an apparatus that performs image processing based on the processing result and arithmetic processing such as predetermined Fourier transform. In the present embodiment, the control / analysis device 8 is a computer having an image display unit that enables execution of control and analysis described in this specification, and irradiation is performed via a control signal line (not shown). The device (optical system), the detection / conversion device 4, the pulse laser light source 2, and the voltage application means 3 for applying a predetermined voltage to the electrode 21 are also controlled.

Further, the control / analysis device 8 controls the width of the depletion layer in the semiconductor 23 by controlling the voltage applied to the electrodes 21, 21,... From the position where the electrodes 21, 21,. The amplitude intensity of the generated pulse electromagnetic wave 10 can be changed. In addition, the control / analysis device 8 controls the voltages applied to the plurality of electrodes 21, 21,. Electromagnetic waves having different intensities and phase differences are generated, and the radiation direction (propagation direction) of the electromagnetic waves can be appropriately controlled using the interference effect of phase waves between these different electromagnetic waves. A method for controlling the propagation direction of the electromagnetic wave using the interference effect of the phase wave will be described later. In this way, the pulse electromagnetic wave 10 generated by the electromagnetic wave wave front shaping element 1 is radiated to the inspection object 30 and the change in the amplitude intensity of the pulse electromagnetic wave 10 transmitted or reflected by the inspection object 30 is captured and analyzed by the control / analysis device 8. Thereafter, by imaging the analysis result, the contents in the inspection object 30 and the chemical composition of the contents can be imaged.
Specifically, by changing the applied voltage of each electrode 21, 21,..., The charge on the surface of the insulator 22 changes, corresponding to the position where each electrode 21, 21,. Wavefront shaping of the pulsed electromagnetic wave 10 generated from the incident surface 23a of the semiconductor 23 can be performed. The test object 30 is irradiated with the pulse electromagnetic wave 10 subjected to wavefront shaping (modulation), the pulse electromagnetic wave 10 transmitted or reflected through the test object 30 is detected, and the pulse electromagnetic wave 10 transmitted (or reflected) is controlled / It becomes possible to collate with a substance-specific electromagnetic frequency database (for example, a terahertz wave frequency database) stored in the storage device in the analysis device 8 and specify the substance of the contents. In this way, the electromagnetic wave imaging apparatus 20 can be used as a so-called nondestructive inspection apparatus.
Imaging of the inspection object 30 is performed by the above apparatus configuration and principle.

  Next, an electromagnetic wave imaging method applied to the electromagnetic wave imaging apparatus 20 configured as described above will be described.

  The electromagnetic wave imaging method according to the present embodiment proceeds according to the flow shown in FIG. 6 and includes an irradiation step S10, an electromagnetic wave emission step S20, an electromagnetic wave control step S30, an electromagnetic wave detection step S40, and an image processing step S50. Has mainly. Hereinafter, each step will be specifically described.

  The irradiation step S <b> 10 is a step of irradiating the incident surface 23 a of the semiconductor 23 with the pulsed laser light 9.

  That is, in the irradiation step S10, when the inspection object 30 is inspected nondestructively, first, as shown in FIG. 1, the inspection object 30 is moved to a predetermined position in the apparatus (in the present embodiment, the light collecting means 18). After being set between the opposing parabolic mirrors), the control / analyzer 8 controls the pulsed laser light 9 emitted from the pulsed laser light source 2 into a beam splitter 14 (in this embodiment, a half mirror). ) Is divided into probe light L1 and pump light L2 (pulse laser light splitting step), and the pump light L2 is irradiated toward the incident surface 23a of the semiconductor 23 in the electromagnetic wavefront shaping element 1.

  The electromagnetic wave radiation step S20 is a step of radiating the pulse electromagnetic wave 10 generated from the incident surface 23a of the semiconductor 23 to the inspection object 30.

  That is, in the electromagnetic wave emission step S20, the pulse electromagnetic wave 10 generated from the incident surface 23a of the semiconductor 23 is emitted to a predetermined region of the inspection object 30. In the electromagnetic wave emission step S <b> 20, the pump light L <b> 2 that is one of the divided pulse laser lights 9 is passed through the optical chopper 16, and the pump light L <b> 2 that has passed through the optical chopper 16 is irradiated onto the incident surface 23 a of the semiconductor 23. The Thus, the pulse electromagnetic wave 10 generated from the incident surface 23 a of the semiconductor 23 corresponding to the electrodes 21, 21,... That is the irradiation position of the pump light L 2 is radiated to the inspection object 30.

  In the electromagnetic wave control step S30, when the pulsed laser light 9 is incident on the semiconductor 23, the applied voltage is controlled by the voltage applying unit 3, so that the semiconductor corresponding to the electrode 21 to which the applied voltage is applied. 23 is a step of controlling the radiation intensity of the pulsed electromagnetic wave 10 generated from the incident surface 23a.

  That is, in the electromagnetic wave control step S30, voltage control is performed individually on the plurality of electrodes 21, 21,... Arranged in an array, thereby corresponding to the positions of the electrodes 21, 21,. A plurality of individually modulated pulsed electromagnetic waves 10 are emitted from the laser light incident surface 23a of the semiconductor 23.

  The electromagnetic wave detection step S40 is a step of detecting the pulsed electromagnetic wave 10 transmitted or reflected by the inspection object 30.

  That is, in the electromagnetic wave detection step S40, the amplitude intensities of the plurality of pulsed electromagnetic waves 10 radiated from the laser light incident surface 23a of the semiconductor 23 corresponding to the respective positions of the plurality of electrodes 21, 21,. Is detected by the detection element 19. The electromagnetic wave detection step S40 further includes a probe light irradiation step and a time series waveform generation step.

  In the probe light irradiation step, the probe light L1 is passed through the time delay means 15 and is irradiated to the detection element 19 in synchronization with the incidence of the pulse electromagnetic wave 10 generated by the pump light L2 on the detection element 19 It is.

  That is, in the probe light irradiation step, the probe light L1, which is one of the divided pulse laser lights 9, is irradiated to the other end of the detection element 19 through the mirror, the time delay means 15, the mirror, and the lens 35. At this time, the probe light L <b> 1 is irradiated in synchronization with the pulse electromagnetic wave 10 generated from the semiconductor 23 being transmitted or reflected by the inspection object 30 and entering the detection element 19.

  The time-series waveform generation step acquires the amplitude intensities of the plurality of pulse electromagnetic waves 10 having different delay times synchronized with the probe light L1, and transmits or reflects the pulse electromagnetic waves 10 transmitted through or reflected from a predetermined region of the inspection object 30. This is a step of generating a time series waveform.

  That is, in the time series waveform generation step, when the probe light L2 divided by the beam splitter 14 passes through the time delay means 15 in the middle of the optical path to the detection element 19, the time delay means 15 has a predetermined value. The probe light L1 is incident and reflected by a movable mirror 15a that is movably arranged in a direction (in this embodiment, parallel to the probe light L2). Further, the control / analysis device 8 periodically reciprocates the movable mirror 15a in a predetermined direction at a predetermined frequency, thereby optically delaying the time for the probe light L1 to reach the detection element 19. Thus, the control / analysis device 8 delays the time when the probe light L1 is incident on the detection element 19 while periodically changing the time when the probe light L1 reaches the detection element 19 by the time delay means 15. It becomes possible to acquire the amplitude intensity of the pulse electromagnetic wave 10 when the probe light L1 is incident in a predetermined time series.

Specifically, the control / analysis device 8 generates a time-series waveform of amplitude intensity based on the amplitude intensity of the detected pulse electromagnetic wave 10. As the process, first, the detection element 19 is inspected. When the pulsed electromagnetic wave 10 transmitted or reflected through the object 30 is collected and synchronized with the incidence of the pulsed electromagnetic wave 10, and the probe light L 1 is irradiated to a predetermined position of the detection element 19, the electric field of the pulsed electromagnetic wave 10 incident upon the irradiation. A current proportional to the intensity (amplitude intensity) is generated. The current is converted into a voltage by the current amplifier 27, and then lock-in detection is performed by the lock-in amplifier 28 in synchronization with the chopping of the optical chopper 16. Then, the lock-in detection value is input to the computer 8. That is, the control / analysis device 8 can detect each amplitude intensity of the pulsed electromagnetic wave 10a incident when the probe light L1 is applied to the detection element 19.
When the electromagnetic wave detection step S40 (probe light irradiation step, time series waveform generation step) is completed, the process proceeds to the image processing step S50.

  The image processing step S50 is a step of performing image processing based on the pulsed electromagnetic wave 10 detected in the electromagnetic wave detection step S40.

  That is, in the image processing step S50, the inspection / target apparatus 30 measures the inspection object 30 qualitatively or quantitatively from the amplitude intensity of the pulse electromagnetic wave 10 by the control / analysis device 8, and performs a predetermined calculation process to perform the inspection object 30. For obtaining a spectral distribution or the like of the substance contained therein, and detecting whether or not the electromagnetic wave amplitude intensity has changed in the electromagnetic wave transmitted or reflected by the inspection object 30 and the amount of change in the electromagnetic wave amplitude intensity. Information such as physical properties and shapes in the object 30 is acquired as an image.

  As described above, the electromagnetic wave wavefront shaping element 1 according to the present invention and the electromagnetic wave imaging apparatus 20 provided with the electromagnetic wave wavefront shaping element 1 apply the applied voltage by the voltage applying unit 3 when the pulse laser beam 9 is incident on the semiconductor 23. By controlling, the radiation intensity of the pulse electromagnetic wave 10 generated from the incident surface 23a of the pulsed laser light 9 of the semiconductor 23 corresponding to the electrode 21 to which the applied voltage is applied can be controlled. Further, the electromagnetic wave imaging apparatus 20 according to the present invention irradiates the entire semiconductor 23 of the electromagnetic wave wavefront shaping element 1 with the pulsed laser light 9 and performs an inspection while controlling the bias of the pulsed electromagnetic wave 10 generated by the irradiation of the pulsed laser light 9. Imaging is performed by detecting the pulse electromagnetic wave 10 radiating to the object 30 and passing (or reflecting) the object 30 and analyzing the detection result.

  Further, in the above series of imaging steps, after the inspection object 30 is set once, the entire region to be inspected is irradiated with the pulsed electromagnetic wave 10 to analyze the substance to be detected in the entire region to be inspected. Since it does not require time and effort for exchanging the filter for wavefront shaping as in the prior art, the workability is good, and a lot of analysis data can be obtained efficiently in a short time. That is, in the electromagnetic wave imaging apparatus 20 provided with the electromagnetic wave wave front shaping element 1 of the present embodiment, filter replacement is unnecessary, and an electromagnetic wave imaging image of the inspection object 30 can be acquired efficiently and at high speed.

  Next, a result of an experiment for controlling the radiation intensity of the pulsed electromagnetic wave 10 performed using the electromagnetic wave imaging apparatus 20 according to the present invention will be described.

  FIG. 7B shows imaging when the pulse electromagnetic wave 10 (in this embodiment, terahertz wave) is emitted without setting the inspection object 30. The range (irradiated surface area) at this time is 13.5 mm (x-axis direction) × 13.5 mm (y-axis direction), and the laser spot diameter is about 450 μm. Note that numbers 1 to 4 arranged in the horizontal direction and A to D arranged in the vertical direction shown in FIG. 6 correspond to the arrangement numbers and arrangement symbols of the electrodes 21 shown in FIG. The left diagram in FIG. 7B is an imaging showing the intensity of the terahertz wave by gradation of gradation. As shown in FIG. 7A, when an applied voltage (+10 V) is applied to each of the electrodes 21, 21,... In a T shape, each of the electrodes 21, 21 as shown in the left diagram of FIG. Imaging corresponding to... Is obtained. The right diagram in FIG. 7B is an imaging of a value obtained by measuring the difference between the bias-controlled portion (applied voltage 10 V) and the Ref portion (0 V) to which no voltage is applied, as in the left diagram in FIG. 7B. It is. The gradation of gradation in the right diagram in FIG. 7B indicates the magnitude of the differential voltage difference. As is clear from this result, a predetermined applied voltage pattern (T-shaped pattern in this experiment) is applied as described above, and the difference between the applied voltage and the Ref portion (no applied voltage) is obtained. Further, it is possible to irradiate the terahertz wave with a desired pattern, and further, it is possible to control the terahertz wave so as to obtain a desired radiation intensity by controlling the applied voltage by the voltage applying means 3.

Next, in order to verify the principle of the electromagnetic wave intensity control described above, the relationship between the terahertz wave intensity and the bias voltage was examined. The results are shown below.
FIG. 8 shows the relationship (bias dependence) between the terahertz wave intensity and the applied voltage. In the graph shown in FIG. 8, an electromagnetic wave waveform shaping element is formed using Ti (titanium) instead of Au as an electrode of the electromagnetic wave waveform shaping element 1, and the semiconductor 23 is irradiated with the pulsed laser light 9. The terahertz wave intensity is measured when a DC bias is applied between (Si). The horizontal axis represents the applied voltage (bias voltage) [V], and the vertical axis represents the terahertz wave intensity (arbitrary unit). As shown in FIG. 8, the terahertz wave intensity and the applied voltage (bias voltage) showed a substantially linear relationship, and it was confirmed that the terahertz wave intensity was dependent on the applied voltage (bias voltage). From this result, it was confirmed that the pulsed electromagnetic wave 10 radiated can be controlled by controlling the applied voltage applied to the electrode 21 by the voltage applying means 3.
From the above experimental results, it was proved that the radiation intensity (generated intensity) of the terahertz wave can be controlled by controlling the voltage applied to the electrode 21 of the electromagnetic wave wavefront shaping element 1.

Next, another example of the electromagnetic wave imaging apparatus according to this embodiment will be described.
FIG. 9 shows another embodiment in which a CCD camera is arranged in place of the detection element 19 in the electromagnetic wave imaging apparatus 20 of the present embodiment. According to this another embodiment, the pulse electromagnetic wave 10 generated from the electromagnetic wave wavefront control element 1 can be emitted to the inspection object 30 and the pulse electromagnetic wave 10 transmitted through the inspection object 30 can be acquired by the CCD camera.
10, in the electromagnetic wave imaging apparatus 20 according to the present embodiment, a concave mirror and a detector that are focusing means are disposed instead of the detection element 19, and a plurality of lenses are disposed in the vicinity of the incident surface 23 a of the electromagnetic wave front shaping element 1. This is another embodiment. According to this other embodiment, the pulse electromagnetic wave 10 generated from the electromagnetic wave wavefront control element 1 is irradiated to the inspection object 30, and the pulse electromagnetic wave 10 transmitted through the inspection object 30 is collected and detected by the concave mirror. Imaging can be performed by image processing.

  Based on the principle of the present invention, the above flow will be described again. (1) When the pulse laser beam 9 (femtosecond laser) is irradiated from the transparent substrate 24 side, the carrier inside the semiconductor 23 is modulated and a terahertz wave is emitted. The (2) By applying a voltage between the electrode 21 and the semiconductor 23 by the voltage applying means 3, the intensity of the terahertz wave that is the pulsed electromagnetic wave 10 generated immediately below the electrode 21 can be controlled. That is, the pattern distribution of the radiation intensity as shown in FIG. 7 can be easily controlled by applying a voltage to the electrodes 21, 21... The element 1 can perform high-speed wavefront control (modulation control) by voltage control of the electrode 21.

  That is, as in the above-described embodiment, the electromagnetic wave wave front shaping element 1 irradiates a MOS capacitor structure using a sapphire substrate with a femtosecond laser, which is a pulse laser beam 9, from the substrate side, thereby generating a terahertz wave that is an example of a pulsed electromagnetic wave. It is an element which can radiate. In the electromagnetic wave wave front shaping element 1, it is possible to control the radiation intensity of the generated terahertz wave by controlling the gate voltage.

  In the present embodiment, as described above, the electromagnetic wavefront shaping element 1 that is a sensing plate having a MOS structure is manufactured, and the experiment for controlling the generation intensity of the terahertz wave by bias control is performed, and the terahertz wave generated from the electromagnetic wavefront shaping element 1 is performed. It was proved that the strength of the steel can be controlled.

  The electromagnetic wavefront shaping element of the present invention is proposed as a new terahertz wave sensing device in order to solve the problems of the prior art, adopts a MOS array structure as a generating element, and controls the voltage applied to this element. Thus, the electromagnetic wave generation intensity can be controlled. The electromagnetic wavefront shaping element of the present invention can generate an electromagnetic wave by irradiating the generating element with a laser pulse of picosecond or less, and can electrically control the wavefront of the generated electromagnetic wave.

  Next, using the same configuration of the electromagnetic wave waveform shaping element 1 described above, experiments and simulations were conducted to determine whether the radiation direction of the pulse electromagnetic wave 10 generated from the electromagnetic wave waveform shaping element 1 can be electrically controlled.

(Terahertz wave radiation direction control method)
Usually, in imaging using pulsed electromagnetic waves, an imaging image is acquired by moving the element itself that generates pulsed electromagnetic waves by a driving means and scanning. According to the present invention, the fact that imaging can be performed using the electromagnetic wave waveform shaping element 1 while the electromagnetic wave waveform shaping element 1 is fixed without moving will be described with reference to the drawings and the simulation results.

(Explanation of terahertz wave generation pattern control)
FIG. 11 shows that the pulse laser beam 9 is incident on the semiconductor at a predetermined incident angle and generated from the incident surface of the semiconductor in each of the case where the electrode shape is a horizontally long shape and the case where the electrode shape is a vertically long shape. This shows terahertz waves. In FIG. 11A, the arrival time of the pulsed laser light 9 is delayed as it goes in the longitudinal direction (rightward direction) of the horizontally long electrode because the pulsed laser light 9 is incident at a predetermined angle. Phenomena with different phases occur in terahertz waves generated at each point (so-called phased array effect works). The plurality of different phases cause interference, and the generation direction of the terahertz wave generated by the interference effect is determined. On the other hand, in FIG. 11B, the pulse laser beam 9 is incident at a predetermined angle, but since the electrode is vertically long, the short direction of the electrode is short, and as a result, the arrival time of the pulse laser beam 9 is delayed. Almost never occurs, and the phase remains the same in the terahertz wave generated at each part of the laser arrival point (the phased array effect does not work). As a result, the terahertz wave is generated in a direction substantially perpendicular to the incident surface.
From the results shown in FIG. 11, it was found that the radiation direction of the terahertz wave can be controlled with the laser incident angle fixed by changing the generation pattern of the terahertz wave. In other words, in the electromagnetic wave waveform shaping element 1, as described above, the applied voltage to the plurality of electrodes 21 is controlled by the voltage applying unit 3, and a terahertz generation pattern such as a horizontal generation pattern or a vertical generation pattern is generated. It was found that the radiation direction of the terahertz wave can be controlled with the laser incident angle fixed by appropriately changing the wave generation pattern. That is, in the electromagnetic wave waveform shaping element 1 of the present embodiment, when the pulse laser beam 9 is incident on the semiconductor 23, the applied voltage is applied by controlling the applied voltage by the voltage applying unit 3, respectively. The radiation direction of the pulse electromagnetic wave 10 generated from the incident surface 23a of the pulsed laser light 9 of the semiconductor 23 corresponding to the electrode 21 can be deflected. Next, the relationship between the generation pattern of the terahertz wave and the propagation direction of the terahertz wave will be described in more detail.

(Terahertz wave propagation simulation)
Next, it was verified by terahertz wave propagation simulation whether the terahertz wave propagation direction can be deflected in a predetermined direction by controlling the generation pattern (applied voltage pattern) of the terahertz wave.
In the terahertz wave propagation simulation, assuming the electrode 21 of the electromagnetic wave waveform shaping element 1, electrode samples are arranged in a 5 × 5 array (referred to as a radiation block) as shown in the left diagram of FIG. 12. 1 block corresponding to one electrode: 90 μm × 90 μm, and the space between the blocks is 10 μm. In the left diagram of FIG. 12, the white block indicates the applied voltage ON, and the black block indicates the applied voltage OFF state. Further, as shown in the right diagram of FIG. 12, the pulse laser beam incident on the semiconductor of the electromagnetic wave waveform shaping element has an incident angle of 45 °, a wave source: a sine wave of a spherical wave, and a wavelength: 300 μm.

FIG. 13 is a result of verifying by simulation a terahertz wave generated corresponding to each of the above-described horizontally and vertically applied voltage patterns. Here, the white block indicates terahertz wave generation (applied voltage ON state), and the black block indicates terahertz wave generation (applied voltage OFF state).
In the horizontally long type, no phase change is generated in the yz plane, but a phase pattern (dark gradation portion) on the upper right side indicating the propagation direction of the terahertz wave is generated in the xz plane. Can be confirmed.
On the other hand, in the vertical type, it can be confirmed that an upper phase pattern (dark gradation portion) indicating the propagation direction of the terahertz wave is generated in the yz plane, but in the propagation direction particularly in the xz plane. There is no directivity.
In each of the horizontally and vertically applied voltage patterns, the same result as the prediction shown in FIG. 11 described above was obtained in the simulation result.

FIG. 14 shows the result of verification by simulation for terahertz waves generated corresponding to the applied voltage patterns of the right diagonal type and the left diagonal type.
In the right diagonal type, it can be confirmed that an upper right phase pattern (dark gradation portion) indicating the propagation direction of the terahertz wave is generated in each of the yz plane and the xz plane.
On the other hand, in the left diagonal type, it can be confirmed that an upper left phase pattern indicating the propagation direction of the terahertz wave is generated on the yz plane, but on the xz plane, an upper right phase pattern (high density) is confirmed. It can be confirmed that a color gradation portion has occurred.
From the above simulation results, it was confirmed that the propagation direction of the terahertz wave was changed by the terahertz wave radiation pattern.

  From the above simulation results, the electromagnetic wave waveform shaping element 1 according to the present embodiment controls the ON or OFF of the applied voltage to the plurality of electrodes 21 by the voltage application unit 3, and the electrode to which the applied voltage is applied. By forming a predetermined pattern of 21, the radiation direction of the pulse electromagnetic wave 10 generated from the pulse laser light incident surface 23 a of the semiconductor 23 corresponding to the electrode 21 on which the predetermined pattern is formed can be deflected. That is, as verified in the above simulation, the electromagnetic wave waveform shaping element 1 is capable of electrically controlling the terahertz wave radiation direction (propagation direction) generated by controlling the voltage applied to the electrode 21. This is a control device, which makes it possible to speed up imaging using terahertz waves.

  Moreover, in the electromagnetic wave imaging apparatus 20 mentioned above, by providing the electromagnetic wave waveform shaping element 1, the inspection object 30 is emitted by radiating the pulse electromagnetic wave 10 to the inspection object 30 and deflecting the radiation direction of the generated pulse electromagnetic wave 10. And a means for detecting the pulse electromagnetic wave 10 transmitted or reflected by the inspection object 30.

  In addition, in the electromagnetic wave control step S30 of the flow shown in FIG. 6, when the pulse laser beam 9 is incident on the semiconductor 23, the applied voltage is controlled by the voltage applying means 3, respectively. By adding an electromagnetic wave scanning step of deflecting the radiation direction of the pulsed electromagnetic wave 10 generated from the pulsed laser light incident surface 23a of the semiconductor 23 corresponding to the electrode 21 to which the inspection object 30 is applied, and scanning the inspection object 30, A scanned image of the object 30 can be acquired.

  As described above, according to the present invention, the elements themselves are arrayed, and wavefront shaping can be performed while generating electromagnetic waves, so that it is not necessary to pass through a wavefront shaping filter. In addition, since it is possible to electrically control the radiation intensity and radiation direction of the generated electromagnetic wave, it is possible to scan the inspection object while performing wavefront shaping in real time, dramatically increasing the electromagnetic wave visualization speed. Can be improved.

  The electromagnetic wavefront shaping element (also referred to as an electromagnetic wavefront control element) of the present invention controls the intensity of the generated terahertz wave by bias control to the metal part of the MOS structure, and patterning the metal part (applied voltage control). By controlling the phase of the terahertz wave by controlling the electromagnetic radiation pattern by ON / OFF of voltage application or the like), the wavefront of the generated terahertz wave can be controlled. In addition, by patterning a plurality of metal parts as in the present invention, the plurality of metal parts become a plurality of wave sources, and the terahertz waves radiated from the plurality of wave sources interfere with each other, and control is made to have an arbitrary phase pattern. It becomes possible to do.

  The present invention relates to an element that controls a wavefront of an electromagnetic wave to be generated at high speed in a technique for generating a high-frequency electromagnetic wave (particularly, a terahertz wave) by irradiating a MOS structure semiconductor with an ultrashort light pulse. According to the present invention, it is possible to apply a two-dimensional Fourier change visualization technique to an electromagnetic wave front at high speed, and high-speed electromagnetic imaging is possible. Further, according to the present invention, the intensity distribution of the generated electromagnetic wave can be used as an active filter for electromagnetic waves by making the intensity distribution periodic.

  The present invention is applicable to the field of terahertz wave electromagnetic wave analysis, and particularly relates to a technique relating to generation of short pulse electromagnetic waves. Examples of application of the present invention include a drug nondestructive inspection device and a protein analyzer.

DESCRIPTION OF SYMBOLS 1 Electromagnetic wave shaping wave front element 8 Control and analysis apparatus 9 Pulse laser beam 10 Pulse electromagnetic wave 21 Electrode 22 Insulator 23 Semiconductor 30 Inspection object

Claims (9)

An electromagnetic wavefront shaping element for performing wavefront shaping on an electromagnetic wave,
Semiconductors,
An insulator formed on the semiconductor;
A plurality of electrodes formed in an array on the insulator;
A voltage applying means for applying a predetermined applied voltage between each of the plurality of electrodes and the semiconductor, and for controlling the applied voltage, respectively;
When pulsed laser light is incident on the semiconductor, the applied voltage is controlled by the voltage applying means, so that an electromagnetic wave generated from the pulsed laser light incident surface of the semiconductor corresponding to the electrode to which the applied voltage is applied. An electromagnetic wavefront shaping element characterized by controlling the radiation intensity of the light. An electromagnetic wave imaging apparatus comprising the electromagnetic wave wave shaping element according to claim 1,
Means for irradiating the pulse laser beam incident surface of the semiconductor with the pulse laser beam;
An electromagnetic wave imaging apparatus comprising: means for radiating an electromagnetic wave generated from an incident surface of the semiconductor pulse laser beam to an inspection object and detecting the electromagnetic wave transmitted or reflected by the inspection object. An electromagnetic wave imaging method applied to an electromagnetic wave imaging device comprising the electromagnetic wave wavefront shaping element according to claim 2,
An irradiation step of irradiating the pulse laser beam incident surface of the semiconductor with the pulse laser beam;
An electromagnetic wave radiation step of radiating an electromagnetic wave generated from the incident surface of the semiconductor pulsed laser light to the inspection object;
When pulsed laser light is incident on the semiconductor, the applied voltage is controlled by the voltage applying means, so that an electromagnetic wave generated from the pulsed laser light incident surface of the semiconductor corresponding to the electrode to which the applied voltage is applied. An electromagnetic wave control process for controlling the radiation intensity of
And an electromagnetic wave detecting step of detecting an electromagnetic wave transmitted or reflected through the inspection object.   The electromagnetic wave imaging method according to claim 3, further comprising an image processing step of performing image processing based on the electromagnetic wave detected by the electromagnetic wave detection step. An electromagnetic wavefront shaping element for performing wavefront shaping on an electromagnetic wave,
Semiconductors,
An insulator formed on the semiconductor;
A plurality of electrodes formed in an array on the insulator;
A voltage applying means for applying a predetermined applied voltage between each of the plurality of electrodes and the semiconductor, and for controlling the applied voltage, respectively;
When pulsed laser light is incident on the semiconductor, the applied voltage is controlled by the voltage applying means, so that an electromagnetic wave generated from the pulsed laser light incident surface of the semiconductor corresponding to the electrode to which the applied voltage is applied. Electromagnetic wavefront shaping element characterized by deflecting the radiation direction of The voltage applying means includes
The semiconductor corresponding to the electrode on which the predetermined pattern is formed by controlling ON or OFF of the applied voltage to the plurality of electrodes, and forming a predetermined pattern made of the electrodes to which the applied voltage is applied. 6. The electromagnetic wave wavefront shaping element according to claim 5, wherein a radiation direction of an electromagnetic wave generated from the incident surface of the pulse laser beam is deflected. An electromagnetic wave imaging apparatus comprising the electromagnetic wave wavefront shaping element according to claim 5 or 6,
Means for irradiating the pulse laser beam incident surface of the semiconductor with the pulse laser beam;
The electromagnetic wave generated from the semiconductor laser beam incident surface is radiated to the inspection object, and the inspection object is scanned by deflecting the radiation direction of the generated electromagnetic wave, and the electromagnetic wave transmitted or reflected by the inspection object. An electromagnetic wave imaging device comprising: An electromagnetic wave imaging method applied to an electromagnetic wave imaging device comprising the electromagnetic wave wavefront shaping element according to claim 7,
An irradiation step of irradiating the pulse laser beam incident surface of the semiconductor with the pulse laser beam;
An electromagnetic wave radiation step of radiating an electromagnetic wave generated from the incident surface of the semiconductor pulsed laser light to the inspection object;
When pulsed laser light is incident on the semiconductor, the applied voltage is controlled by the voltage applying means, so that an electromagnetic wave generated from the pulsed laser light incident surface of the semiconductor corresponding to the electrode to which the applied voltage is applied. An electromagnetic wave scanning step of deflecting the radiation direction of the object and scanning the inspection object;
And an electromagnetic wave detecting step of detecting an electromagnetic wave transmitted or reflected through the inspection object.   The electromagnetic wave imaging method according to claim 8, further comprising an image processing step of performing image processing based on the electromagnetic wave detected by the electromagnetic wave detection step.