PHOTO-THERMO-ACOUSTIC MECHANISM-BASED POWER MEASUREMENT APPARATUS AND MEASUREMENT METHOD FOR TERAHERTZ WAVE AT ROOM TEMPERATURE

Abstract

The present disclosure relates to the technical field of terahertz (THz) wave measurement and relates to a photo-thermo-acoustic mechanism-based power measurement apparatus and measurement method for a terahertz wave at room temperature. The apparatus includes a terahertz wave power modulation component, a photo-thermo-acoustic conversion device, and an acoustic wave measurement component. In the present disclosure, the THz absorbing substance having a photo-thermo-acoustic effect is used as the photo-thermo-acoustic conversion device. A power-modulated terahertz wave is converted into an acoustic wave pulse by means of the photo-thermo-acoustic mechanism. The acoustic wave measurement component measures the acoustic wave pulse. A peak-to-peak value of a pulse of the measured acoustic wave is proportional to the power of the terahertz wave, thereby implementing the fast broadband measurement of the terahertz wave power at room temperature.

Claims

1. A photo-thermo-acoustic mechanism-based power measurement apparatus for a terahertz wave at room temperature, comprising a terahertz wave power modulation component, a photo-thermo-acoustic conversion device, and an acoustic wave measurement component; wherein the terahertz wave power modulation component is configured to irradiate the photo-thermo-acoustic conversion device with an output modulated terahertz wave; the photo-thermo-acoustic conversion device is configured to convert the received modulated terahertz wave into an acoustic wave pulse on the basis of the photo-thermo-acoustic mechanism; the acoustic wave measurement component is configured to measure the acoustic wave pulse; and a peak-to-peak value of the acoustic wave pulse is proportional to power of the modulated terahertz wave, thereby implementing the measurement of the terahertz wave power.

2. The photo-thermo-acoustic mechanism-based power measurement apparatus for a terahertz wave at room temperature according to claim 1, wherein the photo-thermo-acoustic conversion device is made of a terahertz absorbing substance having a photo-thermo-acoustic effect.

3. The photo-thermo-acoustic mechanism-based power measurement apparatus for a terahertz wave at room temperature according to claim 2, wherein the terahertz absorbing substance having a photo-thermo-acoustic effect is graphene foam.

4. The photo-thermo-acoustic mechanism-based power measurement apparatus for a terahertz wave at room temperature according to claim 1, wherein the terahertz wave power modulation component is an optoelectronic modulation component of a terahertz source to be measured, or an external chopper or a semiconductor material irradiated periodically by a modulation light.

5. The photo-thermo-acoustic mechanism-based power measurement apparatus for a terahertz wave at room temperature according to claim 1, wherein the acoustic wave measurement component comprises a microphone, an electrical signal adaptor, and a data recording device.

6. The photo-thermo-acoustic mechanism-based power measurement apparatus for a terahertz wave at room temperature according to claim 1, wherein the apparatus measures the power of the modulated terahertz wave at room temperature by measuring the peak-to-peak value of the acoustic wave pulse.

7. A photo-thermo-acoustic mechanism-based power measurement method for a terahertz wave at room temperature, employing the apparatus according to claim 1, and comprising the following steps: transforming a continuous terahertz wave into a modulated terahertz wave after the continuous terahertz wave passes through a terahertz switch in the terahertz wave power modulation component; irradiating a surface of the photo-thermo-acoustic conversion device by the modulated terahertz wave, and absorbing the modulated terahertz wave by the photo-thermo-acoustic conversion device, resulting in a photo-thermo-acoustic effect; and generating an acoustic wave; receiving the acoustic wave and converting same into a voltage signal by the acoustic wave measurement component; amplifying the voltage signal, and displaying a measurement result of the acoustic wave; a peak-to-peak value of a pulse of the measured acoustic wave being proportional to the power of the modulated terahertz wave, thereby implementing the measurement of the terahertz wave power.

8. The method according to claim 7, wherein the photo-thermo-acoustic conversion device is made of a terahertz absorbing substance having a photo-thermo-acoustic effect.

9. The method according to claim 8, wherein the terahertz absorbing substance having a photo-thermo-acoustic effect is graphene foam.

10. The method according to claim 7, wherein the terahertz wave power modulation component is an optoelectronic modulation component of a terahertz source to be measured, or an external chopper or a semiconductor material irradiated periodically by a modulation light.

11. The method according to claim 7, wherein the acoustic wave measurement component comprises a microphone, an electrical signal adaptor, and a data recording device.

12. The method according to claim 7, wherein the apparatus measures the power of the modulated terahertz wave at room temperature by measuring the peak-to-peak value of the acoustic wave pulse.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic diagram of a measurement apparatus according to one embodiment.

[0019] FIGS. 2A-B illustrate waveform (a) of the modulated terahertz wave of the present disclosure and a waveform (b) of an acoustic wave generated from the terahertz wave.

[0020] FIG. 3 is a schematic diagram of the principle of the photo-thermo-acoustic effect of the present disclosure.

[0021] FIG. 4 is a schematic diagram of the dependence between the peak-to-peak value of acoustic pressure and the terahertz power of the present disclosure.

[0022] Reference numerals in the drawings: 1, continuous terahertz wave source; 2, first off-axis parabolic mirror; 3, second off-axis parabolic mirror; 4, light source; 5, reflector; 6, semiconductor; 7, photo-thermo-acoustic conversion device; 8, microphone; 9, electrical signal adaptor; and 10, oscilloscope.

DETAILED DESCRIPTION

[0023] Hereinafter, the technical solutions of the present disclosure will be completely described with reference to the accompanying drawings. These drawings are simplified schematics for illustrating the basis structure of the present disclosure. The described embodiments are merely some rather than all of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts should fall within the protection scope of the present disclosure.

[0024] The following description of the exemplary example is merely illustrative, and not intended to limit the present disclosure and application or use thereof in any way. Any specific values should be construed merely illustrative and not as a limitation. Thus, other examples of the embodiments may have different values.

Embodiment 1

[0025] The present disclosure provides a photo-thermo-acoustic mechanism-based power measurement apparatus for a terahertz wave at room temperature. The apparatus includes a terahertz wave power modulation component, a photo-thermo-acoustic conversion device, and an acoustic wave measurement component. The specific structure of the apparatus according to the embodiment is as illustrated in FIG. 1. The terahertz wave power modulation component generates an amplitude-modulated terahertz wave. The modulated terahertz wave irradiates the photo-thermo-acoustic conversion device to be converted into an acoustic wave, and is then acquired by the acoustic wave measurement component.

[0026] As shown in FIG. 1, the terahertz wave power modulation component includes a continuous terahertz wave source, a light source, and a semiconductor. Modulation light emitted by a light source 4 passes through a reflector 5 and irradiates the surface of a semiconductor 6; and then, the concentration of photogenerated carriers on the surface of the semiconductor would change during the light irradiation, thereby changing the transmittance of the terahertz wave to the semiconductor. Therefore, the transmittance of the terahertz wave is periodically changed by means of the modulation light. When the terahertz wave emitted by the continuous terahertz wave source 1 propagates through the first and second off-axis parabolic mirrors 2 and 3 to the region on the surface of the semiconductor 6 irradiated by the modulation light, the terahertz wave is modulated by the semiconductor into the amplitude-modulated terahertz wave. According to the embodiment, the terahertz wave is from a 0.1 THz continuous source, irradiating the semiconductor surface at a power of about 22 mW. The semiconductor is an intrinsic silicon wafer having a diameter of about 100 mm and a thickness of 500 μm. The modulation light is a femtosecond laser having a pulse width of 50 fs, a center wavelength of 800 nm, and a repetition rate of 50 Hz. The diameter of the spot irradiating the silicon wafer is about 2 cm. The diameter of the terahertz wave irradiating the semiconductor surface is about 1.9 cm. The waveform of the modulated terahertz wave is shown in FIG. 2A.

[0027] The photo-thermo-acoustic conversion device 7 performs the photo-thermo-acoustic conversion based mainly on the photo-thermo-acoustic mechanism. According to the photo-thermo-acoustic principle, light absorbed by a material would be converted into heat, which will then heat a surrounding air layer to expand the air layer; correspondingly, when the light disappears, the surrounding air layer will cool and compress; the expansion and compression of the air layer produces the acoustic waves. Therefore, the acoustic waves can only be generated when the light energy changes abruptly, and the acoustic waves cannot be generated under constant light energy. The photo-thermo-acoustic mechanism is as illustrated in FIG. 3. In order to obtain a higher photothermal conversion coefficient, the photo-thermo-acoustic conversion material requires a lower heat capacity per unit area (HCPUA). The photo-thermo-acoustic conversion device used in the present disclosure is a two-dimensional material, such as the graphene foam. Graphene, which is the thinnest known material, has an extremely low HCPUA. Compared with the single-layer graphene, graphene foam is three-dimensional and can stand on its own, without requiring a substrate for support. Therefore, the energy does not dissipate to the substrate, and the graphene foam can more effectively improve photo-thermo-acoustic conversion efficiency. The graphene foam according to the embodiment is a cylinder with a diameter of about 10 mm and a thickness of about 1.5 mm

[0028] The acoustic wave measurement component is mainly composed of a microphone 8, an electrical signal adaptor 9 and an oscilloscope 10. The microphone converts an acoustic wave signal into an electrical signal, and the electrical signal adaptor would moderately amplify the signal while supplying power to the microphone, and then the signal is displayed on the oscilloscope. According to the embodiment, since the amplitude of the modulated terahertz wave irradiating the surface of the graphene foam changes for a very short time, less than 15 μs, only one acoustic wave signal is generated for one amplitude change, as shown in FIG. 2B. The response time of the acoustic wave is about 30 μs, including a fall time, about 8 μs and a rise time, about 19 μs. The response time is much shorter than that of a commercial photothermal terahertz detector. By calibrating the responsivity, the peak-to-peak value of the acoustic wave pulse can be converted into THz power. As illustrated in FIG. 4, the terahertz power corresponding to the peak-to-peak acoustic pressure of different acoustic wave pulses shows that there is a linear relationship between the terahertz power and the peak-to-peak acoustic pressure, and the responsivity obtained by fitting is about 3.26 Pa/W. Therefore, the THz power corresponding to the peak-to-peak acoustic pressure of 59 mPa acoustic wave in FIG. 2B is about 18.1 mV. The microphone is cylindrical with a diameter of about 7 mm and a length of about 53 mm. The distance between the front surface of the microphone and the back surface of the graphene foam is about 2 mm, and the detection frequency range of the microphone is 4 Hz-100 kHz. Herein, the magnification of the electrical signal adaptor is 100. The microphone, the electrical signal adaptor and the oscilloscope are connected by a coaxial cable.

[0029] Having thus described the basic concept of the invention, it will be rather apparent to those skilled in the art that the foregoing detailed disclosure is intended to be presented by way of example only, and is not limiting. Various alterations, improvements, and modifications will occur and are intended to those skilled in the art, though not expressly stated herein. These alterations, improvements, and modifications are intended to be suggested hereby, and are within the spirit and scope of the invention. Additionally, the recited order of processing elements or sequences, or the use of numbers, letters, or other designations therefore, is not intended to limit the claimed processes to any order except as may be specified in the claims. Accordingly, the invention is limited only by the following claims and equivalents thereto.