CN116008218A - Terahertz double-optical-comb imaging system - Google Patents
Terahertz double-optical-comb imaging system Download PDFInfo
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- CN116008218A CN116008218A CN202211599835.4A CN202211599835A CN116008218A CN 116008218 A CN116008218 A CN 116008218A CN 202211599835 A CN202211599835 A CN 202211599835A CN 116008218 A CN116008218 A CN 116008218A
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Abstract
The invention relates to a terahertz double-optical-comb imaging system, which comprises: the device comprises a first quantum cascade laser, a second quantum cascade laser, a first light path, a second light path and a spectrum analyzer; the first quantum cascade laser works in an optical frequency comb mode and is used as a sampling optical frequency comb source for emitting terahertz light; the first optical path is used for converging the terahertz light to a sample to be detected to obtain a sampling optical frequency comb signal; the second light path is used for coupling the sampling optical frequency comb signal transmitted through the sample to be detected into the resonant cavity of the second quantum cascade laser; the second quantum cascade laser works in an optical frequency comb mode and is used as an intrinsic optical frequency comb for realizing sampling optical frequency comb signals and multi-heterodyne beat frequency of the intrinsic optical frequency comb signals to obtain double optical comb signals; the spectrum analyzer is used for analyzing and recording the double optical comb signals. The invention can realize sample imaging and spectral characteristic analysis at the same time.
Description
Technical Field
The invention relates to the application field of semiconductor photoelectric devices, in particular to a terahertz double-optical-comb imaging system.
Background
The optical frequency comb is a coherent laser source composed of a series of frequency lines distributed at equal intervals, is expressed as ultrashort pulses with a fixed phase relation in the time domain, has the characteristics of high frequency stability, low phase noise and the like, and can be used in astronomy, time synchronization, communication, absolute distance measurement and other fields. Based on the characteristic of high frequency stability, the method can also be used for absolute frequency calibration and high-resolution spectrum measurement.
The double optical comb is the direct application of the optical frequency comb in high-precision measurement, and the two optical frequency combs with similar repetition frequencies form a multi-heterodyne spectrum of down-conversion on beat frequency through adjacent modes, which is called as the double optical comb. Based on heterodyne sampling of two optical frequency combs, the double optical comb can realize fast measurement with wide band, high resolution and high sensitivity.
Terahertz (THz) wave band covers the characteristic spectrum of a plurality of biological macromolecules, can be used for nondestructive detection of active biological tissues based on non-ionization characteristics, has important application in biomedical detection and imaging, and the development of the optical frequency comb technology of the THz wave band is an effective way for expanding the application of high-precision tips of the optical frequency comb technology. The Quantum Cascade Laser (QCL) is an ideal carrier of the THz wave band optical frequency comb, has the advantages of small volume, high power, easy on-chip integration and the like, and the unique laser self-detection mechanism can further simplify equipment and get rid of dependence on a THz detector.
Disclosure of Invention
The invention aims to solve the technical problem of providing a terahertz double-optical-comb imaging system which can simultaneously realize sample imaging and spectral characteristic analysis.
The technical scheme adopted for solving the technical problems is as follows: provided is a terahertz double-optical-comb imaging system, comprising: the device comprises a first quantum cascade laser, a second quantum cascade laser, a first light path, a second light path and a spectrum analyzer; the first quantum cascade laser works in an optical frequency comb mode and is used as a sampling optical frequency comb source for emitting terahertz light; the first optical path is used for converging the terahertz light to a sample to be detected to obtain a sampling optical frequency comb signal; the second light path is used for coupling the sampling optical frequency comb signal transmitted through the sample to be detected into the resonant cavity of the second quantum cascade laser; the second quantum cascade laser works in an optical frequency comb mode and is used as an intrinsic optical frequency comb for realizing sampling optical frequency comb signals and multi-heterodyne beat frequency of the intrinsic optical frequency comb signals to obtain double optical comb signals; the spectrum analyzer is used for analyzing and recording the double optical comb signals.
The first quantum cascade laser is connected with a mixed port of a first T-shaped biaser, a direct current port of the first T-shaped biaser is connected with a first power supply, and an alternating current port of the first T-shaped biaser is disconnected.
The second quantum cascade laser is connected with a mixed port of a second T-shaped biaser, a direct current port of the second T-shaped biaser is connected with a second power supply, and an alternating current port of the second T-shaped biaser is connected with the spectrum analyzer.
An amplifier and a band-pass filter are sequentially arranged between the alternating current port of the second T-shaped biaser and the spectrum analyzer, and the amplifier is used for amplifying the double optical comb signals; the band-pass filter is used for filtering noise signals.
The amplifier is a microwave low-noise amplifier, and the bandwidth is larger than that of the double optical comb signals.
The first light path and the second light path are both formed by two off-axis parabolic mirrors.
The sample to be measured is arranged on an electric control two-dimensional displacement table, and the electric control two-dimensional displacement table is positioned on the focal plane of the first light path and used for controlling the electric control two-dimensional displacement table to perform two-dimensional movement on the focal plane.
The terahertz double-optical-comb imaging system also comprises a computer, wherein the computer is respectively connected with the electric control two-dimensional displacement table and the spectrum analyzer, and the computer is used for synchronously controlling the electric control two-dimensional displacement table to move the sample to be detected and record double-optical-comb data obtained by the spectrum analyzer at the corresponding position in real time.
Advantageous effects
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages and positive effects: the invention can utilize single comb tooth imaging of the double optical combs, can also be based on multi-comb tooth cooperative high-precision imaging, has higher resolution compared with an intensity imaging system of a single-frequency laser and a detector, can invert the spectrum characteristic of a sample in real time, realizes THz spectrum detection of the sample, and simultaneously images the spectrum.
Drawings
FIG. 1 is a schematic diagram of an embodiment of the present invention;
fig. 2 is a structural diagram of an embodiment of the present invention.
Detailed Description
The invention will be further illustrated with reference to specific examples. It is to be understood that these examples are illustrative of the present invention and are not intended to limit the scope of the present invention. Further, it is understood that various changes and modifications may be made by those skilled in the art after reading the teachings of the present invention, and such equivalents are intended to fall within the scope of the claims appended hereto.
The embodiment of the invention relates to a terahertz double-optical-comb imaging system, which carries out multi-heterodyne beat frequency on a sampling optical frequency comb signal and an intrinsic optical frequency comb signal which are absorbed by a sample, so that the sampling optical frequency comb signal is down-converted into a GHz double-optical-comb signal, when the sample is positioned at different positions, the absorption of the terahertz signal is different, so that different double-optical-comb spectrums can be generated, the position of the sample corresponds to the double-optical-comb spectrums one by one, and the sample imaging can be realized by comprehensive analysis.
The principle of this embodiment is shown in FIG. 1, and the THz band has a repetition frequency f r And the repetition frequency is f r +Δf r The intrinsic optical frequency comb signal is subjected to heterodyne beat frequency among comb teeth to obtain a double optical comb signal which is down-converted to GHz, and the repetition frequency of the double optical comb is delta f r . When the sample is absorbed, the intensity of the comb teeth of the sampling optical frequency comb signal is correspondingly attenuated, and the double optical combs with corresponding attenuation are obtained with the beat frequency of the original optical frequency comb signal. Recording the position of the sample and the corresponding double optical comb signals, and comprehensively analyzing to realize sample imaging.
As shown in fig. 2, the terahertz double-optical-comb imaging system includes: the device comprises 2 quantum cascade lasers, 2T-shaped biasers, 2 laser power supplies, 4 off-axis parabolic mirrors, a band-pass filter, an amplifier, a spectrum analyzer, an electric control two-dimensional displacement table and a computer. The THz light emitted by the sampling optical frequency comb is converged on a sample to be measured positioned on a focal plane through two off-axis parabolic mirrors (OAPs), transmitted light transmitted through the sample to be measured is coupled into a cavity of an intrinsic optical frequency comb after passing through the other two off-axis parabolic mirrors, multi-heterodyne beat frequency of the sampling optical frequency comb signal and the intrinsic optical frequency comb signal is realized, the double optical comb signal is obtained by direct self detection of the quantum cascade laser serving as the intrinsic optical frequency comb, and is analyzed and recorded by a spectrum analyzer after being amplified by a microwave low-noise amplifier and filtered by a band-pass filter, and the two-dimensional translation table and the spectrum analyzer for placing the sample to be measured can be synchronously acquired through a computer and imaged by a PC in real time.
The quantum cascade laser in this embodiment all works in an optical frequency comb mode, and is divided into a sampling optical frequency comb and an intrinsic optical frequency comb, signals sent by the sampling optical frequency comb are converged to a focus through two off-axis parabolic mirrors, and are coupled into a cavity of the intrinsic optical frequency comb through another two off-axis parabolic mirrors after passing through a sample to be detected, the sampling optical frequency comb signals and the intrinsic optical frequency comb signals perform multi-heterodyne beat frequency, and the obtained double optical frequency comb signals are obtained through self-detection of the intrinsic optical frequency comb QCL.
The mixing ports of the two T-shaped biasers in the embodiment are respectively connected with the respective optical frequency combs, and the direct current ports are connected with a power supply to supply power to the optical frequency combs; the difference is that the alternating current port of the T-shaped biaser 1 is disconnected and not connected; the alternating-current end of the T-shaped biaser 2 is connected with an amplifier and is used for outputting a double optical comb signal obtained by self-detection of the intrinsic optical frequency comb.
The amplifier in this embodiment is a microwave low noise amplifier, the input end of the amplifier is connected with the AC port of the T-type bias device 2, the output end of the amplifier is connected with the band-pass filter, and the amplifier is used for amplifying the double optical comb signals obtained by self-detection, providing 30dB signal gain, and the bandwidth of the amplifier should be greater than the bandwidth of the double optical comb signals, so as to realize the whole amplification of the double optical comb signals, and meet the detection requirement of the subsequent spectrum analyzer on the signal intensity.
The band-pass filter in the embodiment is used for filtering out the double optical comb signals and reducing the influence of other radio frequency signals such as inter-mode beat signals of the optical frequency comb on the detection of the double optical comb signals. The input port of the band-pass filter is connected with the output port of the amplifier, and the output port is connected with the spectrum analyzer.
The spectrum analyzer in this embodiment is linked with the output port of the band-pass filter, and is used for detecting and recording in real time to obtain the filtered double optical comb signals. The electronic control two-dimensional displacement table in the embodiment is used for placing a sample, ensuring that the sample moves in two dimensions on a focal plane, and is controlled by a computer, and the computer is used for synchronously controlling the electronic control two-dimensional displacement table to move the sample in real time and recording double optical comb data of a corresponding position spectrum analyzer, so that imaging is realized.
The invention is further illustrated by a specific example.
In the embodiment, the optical frequency combs are terahertz quantum cascade laser optical frequency combs, the lasing frequency of the laser linearly moves along with the driving current, the center frequency of the sampling optical frequency comb is 4.2THz, the repetition frequency is 6.2GHz, the center frequency of the intrinsic optical frequency comb is also 4.2THz, the repetition frequency is 6.21GHz, and the repetition frequency of the terahertz optical frequency comb for generating down-conversion double optical combs is 10MHz. The minimum comb tooth pair spacing corresponding to the optical frequency comb 1 and the optical frequency comb 2 is 5.5GHz, namely, the double optical comb carrier generated by mixing the optical frequency comb 1 and the optical frequency comb 2 is 5.5GHz. In performing imaging of a sample, comprising the steps of:
step S1: the method comprises the steps that 4 off-axis parabolic mirrors are provided, the sizes of the off-axis parabolic mirrors are matched with the sizes of light spots emitted by a laser, the diameters of the off-axis parabolic mirrors are 2 inches, the focal length of the off-axis parabolic mirrors is 4 inches, the off-axis parabolic mirrors 1 are used for converting divergent light emitted by a signal light frequency comb into parallel light, the off-axis parabolic mirrors 2 collect the parallel light on a sample, transmitted light is collected by the off-axis parabolic mirrors 3 and converted into parallel light, and the parallel light is collected by the off-axis parabolic mirrors 4 and collected into an intrinsic light frequency comb.
Step S2: and providing 2 laser current sources for respectively supplying power to the sampling optical frequency comb and the intrinsic optical frequency comb. Two T-type biasers are provided for the transmission of the direct current signal and the optical frequency comb radio frequency signal of the current source. The T-shaped biaser connected with the intrinsic optical frequency comb is also connected with the amplifier and the optical frequency comb by a high-frequency coaxial cable; the current source connects the T-type biaser and the optical frequency comb by a coaxial cable.
Step S3: a microwave low-noise amplifier is provided for amplifying double optical comb signals, 30dB gain can be provided, the working range is 1-18GHz, and the low-noise amplifier is connected with other devices through high-frequency coaxial cables.
Step S4: a band-pass filter with the working bandwidth of 5GHz-6GHz is provided for filtering out complete double optical comb signals, and the band-pass filter is connected with a spectrum analyzer and a low noise amplifier through a high-frequency coaxial cable.
Step S5: a spectrum analyzer is provided, the working range is 2Hz-26.5GHz, and the spectrum analyzer is used for detecting the double optical comb signals after recording, amplifying and filtering.
Step S6: a two-dimensional sample translation stage is provided for controlling the movement of the sample in the focal plane with a minimum movement step size of 0.5 μm.
Step S7: and providing a computer, synchronously controlling the two-dimensional sample translation stage and the spectrum analyzer by using a Labview program, recording one group of data at each moving position, and recording double optical comb signals in real time to realize imaging of the sample.
It is easy to find that the QCL of two THz wave bands is used as an optical frequency comb light source, light emitted by the sampling optical frequency comb is detected by the intrinsic optical frequency comb after passing through the sample, down-converted multi-heterodyne double optical comb signals are obtained between two optical frequency comb teeth in beat frequency mode, one-to-one correspondence exists between the double optical comb signals and the sample position, and sample imaging can be achieved through analysis of the comb tooth signals of the double optical comb. The invention can utilize single comb tooth imaging of the double optical combs, can also be based on multi-comb tooth cooperative high-precision imaging, has higher resolution compared with an intensity imaging system of a single-frequency laser and a detector, can invert the spectrum characteristics of a sample in real time, realizes THz spectrum detection of the sample, and simultaneously images the imaging spectrum, thereby being beneficial to promoting the high-precision application of THz wave bands in the biomedical field.
Claims (8)
1. A terahertz dual optical comb imaging system, comprising: the device comprises a first quantum cascade laser, a second quantum cascade laser, a first light path, a second light path and a spectrum analyzer; the first quantum cascade laser works in an optical frequency comb mode and is used as a sampling optical frequency comb source for emitting terahertz light; the first optical path is used for converging the terahertz light to a sample to be detected to obtain a sampling optical frequency comb signal; the second light path is used for coupling the sampling optical frequency comb signal transmitted through the sample to be detected into the resonant cavity of the second quantum cascade laser; the second quantum cascade laser works in an optical frequency comb mode and is used as an intrinsic optical frequency comb for realizing sampling optical frequency comb signals and multi-heterodyne beat frequency of the intrinsic optical frequency comb signals to obtain double optical comb signals; the spectrum analyzer is used for analyzing and recording the double optical comb signals.
2. The terahertz double-optical-comb imaging system of claim 1, wherein the first quantum cascade laser is connected to a hybrid port of a first T-type biaser, a direct current port of the first T-type biaser is connected to a first power supply, and an alternating current port is disconnected.
3. The terahertz double-optical-comb imaging system according to claim 1, wherein the second quantum cascade laser is connected to a hybrid port of a second T-type biaser, a dc port of the second T-type biaser is connected to a second power supply, and an ac port is connected to the spectrum analyzer.
4. The terahertz double optical comb imaging system as set forth in claim 3, wherein an amplifier and a band-pass filter are sequentially disposed between the ac port of the second T-type biaser and the spectrum analyzer, the amplifier being configured to amplify the double optical comb signal; the band-pass filter is used for filtering noise signals.
5. The terahertz double-optical-comb imaging system of claim 4, wherein the amplifier is a microwave low-noise amplifier and has a bandwidth greater than that of the double-optical-comb signal.
6. The terahertz double-optical-comb imaging system of claim 1, wherein the first optical path and the second optical path are each constituted by two off-axis parabolic mirrors.
7. The terahertz double-optical-comb imaging system according to claim 1, wherein the sample to be measured is placed on an electronically controlled two-dimensional displacement stage, and the electronically controlled two-dimensional displacement stage is located at a focal plane of the first optical path and is used for controlling the electronically controlled two-dimensional displacement stage to perform two-dimensional movement on the focal plane.
8. The terahertz double-optical-comb imaging system according to claim 7, further comprising a computer, wherein the computer is respectively connected with the electric control two-dimensional displacement table and the spectrum analyzer, and the computer is used for synchronously controlling the electric control two-dimensional displacement table to move the sample to be measured and record double-optical-comb data obtained by the spectrum analyzer at corresponding positions in real time.
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