CN106374323B - Laser up-conversion terahertz difference frequency source detection system - Google Patents
Laser up-conversion terahertz difference frequency source detection system Download PDFInfo
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- CN106374323B CN106374323B CN201611055844.1A CN201611055844A CN106374323B CN 106374323 B CN106374323 B CN 106374323B CN 201611055844 A CN201611055844 A CN 201611055844A CN 106374323 B CN106374323 B CN 106374323B
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- H01S1/00—Masers, i.e. devices using stimulated emission of electromagnetic radiation in the microwave range
- H01S1/02—Masers, i.e. devices using stimulated emission of electromagnetic radiation in the microwave range solid
Abstract
The invention discloses a laser up-conversion terahertz difference frequency source detection system, which is based on the principle of nonlinear optical laser up-conversion, performs up-conversion detection on the existing terahertz pulse difference frequency signal in a nonlinear crystal, realizes terahertz near infrared light detection according to a high-sensitivity near infrared detector and a narrow-band filter technology, and finally realizes room temperature high-speed real-time detection of terahertz waves. The system solves the problem of low-temperature detection limitation of the existing terahertz difference frequency source, and has the advantages of high measurement speed, room temperature detection, small volume, compact structure, high signal-to-noise ratio and the like, and is convenient for real-time pulse signal detection.
Description
Technical Field
The invention relates to a terahertz difference frequency source detection system, in particular to a method for realizing room temperature high-sensitivity detection of a terahertz difference frequency source pulse signal by utilizing near infrared laser up-conversion.
Background
Terahertz technology (0.1 THz-10 THz) is known as one of ten key scientific technologies for changing the future world, and has wide application background in the fields of national defense safety, space communication, biomedical treatment, environmental monitoring, food safety, scientific research and the like.
Research on high-performance terahertz radiation sources is always an important research direction in the field of terahertz research, and the breakthrough of the technology greatly promotes the practical application development of the terahertz technology. At present, among the terahertz radiation sources, the terahertz radiation source generated based on the nonlinear difference frequency technology has the advantages of compact volume, narrow line width, wide tuning range, continuous and adjustable wavelength, high radiation power, room temperature operation and the like, and is considered to be an ideal terahertz radiation source.
At present, a terahertz detector (such as Gao Laiguan and a pyroelectric detector) based on room temperature heat is mainly used for detecting terahertz radiation source signals, and the terahertz radiation source signal detection device has the advantages of full-band response, room temperature operation and the like. However, for terahertz difference frequency source beams, which are generally generated by the difference frequency action of two near infrared nanosecond pulse laser signals with similar wavelengths in a nonlinear terahertz crystal, the pump beam has low working frequency (generally 10 Hz) and is interrupted for a long time (nanosecond order), so that the terahertz pulse signals have extremely low pulse duty ratio (1:10 7 ). Therefore, a room temperature terahertz detector that responds in real time at a high speed, or a terahertz detector that is higher in sensitivity is theoretically required. However, no document is reported at present about the research work of a high-speed real-time room temperature terahertz detector with full-band response. Meanwhile, as the room temperature thermal base terahertz detector (Gao Laiguan, pyroelectric detector) has longer response time (millisecond level), the response rate is not high enough, and the detection requirement of terahertz difference frequency source signals is not met, a liquid helium cryogenic refrigeration bolometer with higher sensitivity is often used in practice (the response time is still millisecond level). At the moment, for detecting the terahertz difference frequency source nanosecond pulse signal, extra noise is introduced, so that only the average power of terahertz pulses can be obtained, and the terahertz pulse signal cannot be detected in real time; the deep low-temperature refrigeration working condition is required, and additional temperature-changing matched equipment is introduced, so that miniaturization is impossible, and practical application and popularization are inconvenient.
Disclosure of Invention
Aiming at the limitations in the current terahertz pulse difference frequency source detection, the invention carries out room-temperature real-time detection on the high-speed pulse terahertz signal based on the principle of laser up-conversion, improves the detection signal-to-noise ratio, gets rid of the low-temperature detection limitation, reduces the equipment volume and promotes the practical application of the terahertz pulse difference frequency source.
The following describes the principle of laser up-conversion generation and the specific generation process in detail:
the principle of generation by conversion on laser belongs to the field of nonlinear optics and frequency, and specifically means that a strong near-infrared pump light (such as 1064 nm) is utilized to detect a terahertz light beam with weak signals, the two light beams simultaneously act on a nonlinear crystal, and when three light photon energy conservation and crystal phase matching conditions are simultaneously met, another near-infrared signal light beam with longer wavelength than the pump light beam is radiated in the crystal, and finally detected by a mature high-sensitivity near-infrared detector. The laser up-conversion generation principle is similar to the terahertz laser difference frequency generation principle, and belongs to the category of the second-order nonlinear optical interaction field.
The method comprises the following steps:
in the laser up-conversion generation process, a high-power pump laser beam omega 1 Terahertz beam ω 2 At the same time, the laser light enters the nonlinear crystal 1, and under the condition that specific conditions (namely photon energy conservation and crystal phase matching conditions) are met, the phenomenon of laser light up-conversion is generated, and the generation of signal light with another low photon frequency can be observed.
Specific photon energy conservation and crystal phase matching conditions can be expressed by the following formulas:
ω 1 -ω 2 ＝ω 3 (one)
The formula (I) is three-photon energy conservation, wherein omega 1 、ω 2 、ω 3 Respectively pump beam, terahertz beam and signal beam photon energy; (II) is the momentum of three light photonsConservation conditions, also known as crystal phase matching conditions, are vector conservation conditions.
Considering the collineation condition of the pump beam, terahertz beam and signal beam, (II) can be changed into K 1 -K 2 ＝K 3 。
In the invention, the nonlinear crystal material used not only comprises inorganic crystal of gallium selenide, gallium phosphide, zinc germanium phosphide and cadmium telluride, but also comprises organic nonlinear crystal material of OH1, DAST and DSTMS.
The invention has the advantages of simple structure, real-time and rapid detection at room temperature, high detection signal-to-noise ratio, no low-temperature detection limitation, reduced equipment volume, easy miniaturization, and promotion of the practical application development of terahertz pulse difference frequency sources in the fields of national defense safety, space communication, biomedical treatment, environmental monitoring, food safety, airport security inspection, scientific research and the like.
Drawings
Fig. 1 is a schematic diagram of the terahertz laser upconversion principle. In the figure, 1 is a nonlinear optical crystal;
the pump light, the terahertz light and the signal light photon momentum are respectively.
Fig. 2 is a diagram of a terahertz laser upper conversion detection experimental device. In the figure, 1 is a high-power 1064nm near-infrared nanosecond laser; 2 is a half wave plate; 3 is an optical parametric oscillator; 4 is a beam delay line; 5 is a polarization beam splitter prism; 6 is a first lens; 7 is a first nonlinear optical crystal; 8 is a near infrared filter; 9 is a first off-axis parabolic mirror; 10 is a laser mirror; 11 is a second lens; 12 is a second nonlinear optical crystal; 13 is a second off-axis parabolic mirror; 14 is a near infrared narrow band filter; 15 is a near infrared spectrometer; 16 is a near infrared detector; reference numeral 17 denotes a vacuum chamber.
Detailed Description
The following describes the specific operation of the terahertz laser up-conversion detection experimental system as follows:
after the radiation output 1064nm laser of the high-power 1064nm near-infrared nanosecond laser 1 passes through the half-wave plate 2, laser beams with the wavelength similar to that output by the optical parametric oscillator 3 (such as 1070 nm) vertically enter the polarization beam splitting prism 5 after passing through the beam delay line 4, the two beams of light reach a collinear state in space and time, are focused by the first lens 6 and then enter the first nonlinear crystal 7, under the specific phase matching condition, high-power terahertz light radiation is generated, and under the action of the near-infrared filter 8, only the terahertz light beam passes through the first off-axis parabolic mirror 9, and finally is focused into the second nonlinear optical crystal 12 after passing through the second off-axis parabolic mirror 13, so as to participate in the terahertz laser up-conversion detection experiment. The half wave plate 2 has the function of changing the polarization state of 1064nm, so that the 1064nm pump beam is divided into two pump beams, one pump beam is reflected to the first nonlinear crystal 7 through the polarization beam splitting prism, the other pump beam is transmitted and output from the other pump beam, the other pump beam is incident to the second nonlinear crystal 12 through the laser reflecting mirror 10 and the second lens 11, a signal beam with the wavelength similar to that of the 1064nm laser beam is generated under the action of laser up-conversion, the signal beam is emitted to the near infrared narrow band filter 14 through a small hole in the second off-axis parabolic mirror 13, the 1064nm laser beam in the optical path is completely absorbed, the signal wavelength of the signal beam is finally detected by the near infrared spectrometer 15, and the radiation power of the signal beam is detected by the near infrared detector 16. The system is introduced into the vacuum chamber 17 at the terahertz generation, transmission and detection part, so that the interference of water vapor in the air on terahertz absorption can be avoided.
The function of the optical elements in the system is described below:
1 is a high-power 1064nm near-infrared nanosecond laser, and a US Continuum Sunlite 1064nm laser is adopted to provide high-power pumping light required by a terahertz difference frequency source;
2 is a half-wave plate, and the polarization direction of 1064nm laser is regulated to form an angle of 45 degrees with the horizontal polarization direction on the incident plane;
3 is an optical parametric oscillator, which provides another near-infrared pumping laser with high power and similar wavelength for the terahertz difference frequency source;
4 is a beam delay line, which is formed by a reflection light path composed of 4 reflection mirrors, and the 1064nm light beam and the output light beam of the optical parametric oscillator are synchronized in time, and the delay time is about 4ns;
a polarization beam splitter prism is adopted to split a 1064nm laser beam into two beams of energy, one beam of the laser beam is reflected to participate in a terahertz difference frequency generation light path, and the other beam of the laser beam is transmitted to be used as a pump beam for terahertz up-conversion detection;
6 is a first lens to focus two near infrared pump beams into a first nonlinear optical crystal;
7 is a first nonlinear optical crystal which generates terahertz optical radiation under the action of a difference frequency;
8 is a near infrared filter, which absorbs and filters 1064nm pump beam and signal beam, and only allows terahertz light to penetrate;
9 is a first off-axis parabolic mirror, and the generated terahertz light is changed into parallel light to be incident into a second off-axis parabolic mirror;
10 is a laser reflector, and part of 1064nm laser is incident into a second nonlinear optical crystal for terahertz light up-conversion detection;
11 is a second lens focusing the portion 1064nm laser light into a second nonlinear optical crystal;
12 is a second nonlinear optical crystal, which performs terahertz light up-conversion detection and radiates near infrared signal light with another wavelength;
a second off-axis parabolic mirror for focusing terahertz light into the second nonlinear optical crystal, and simultaneously, a small hole is formed in the center of the second off-axis parabolic mirror, so that a signal beam generated by a terahertz up-conversion optical path can conveniently pass through the external space of the small hole for detection;
a 14 near infrared narrow band filter for completely filtering 1064nm pump beam and only transmitting signal beam;
15 is a near infrared spectrometer for detecting signal light wavelength;
16 is a near infrared detector for detecting the energy of the signal light;
and 17 is a vacuum chamber, which covers the whole terahertz light beam propagation path and avoids the interference of water vapor in the air on terahertz absorption.
Claims (2)
1. A detection system for a terahertz difference frequency source converted on laser light comprises a high-power 1064nm nanosecond laser (1), a half-wave plate (2), an optical parametric oscillator (3), a beam delay line (4), a polarization beam splitting prism (5), a first lens (6), a first nonlinear optical crystal (7), a near infrared filter (8), a first off-axis parabolic mirror (9), a laser reflector (10), a second lens (11), a second nonlinear optical crystal (12), a second off-axis parabolic mirror (13), a near infrared narrow-band filter (14), a near infrared spectrometer (15), a near infrared detector (16) and a vacuum chamber (17); the method is characterized in that:
the high-power 1064nm nanosecond laser (1) emits laser into the polarization beam splitting prism (5) through the half-wave plate (2), the optical parametric oscillator (3) emits laser into the polarization beam splitting prism (5) through the beam delay line (4), the two laser beams are combined in the polarization beam splitting prism (5) and then are emitted to the first lens (6) and the first nonlinear optical crystal (7) together to generate high-power terahertz light, the terahertz light is collected and focused by the first off-axis parabolic mirror (9) and the second off-axis parabolic mirror (13) to participate in terahertz upper conversion detection in the second nonlinear optical crystal (12), and the residual near infrared combined beam is absorbed by the near infrared filter (8); the laser beam emitted by the 1064nm nanosecond laser (1) is reflected to the second lens (11) and the second nonlinear optical crystal (12) by the laser reflector (10) after passing through the half-wave plate (2) and the polarization beam splitter prism (5), and is subjected to terahertz light up-conversion detection, so that near infrared signal light radiation with the other wavelength is realized; the signal light passes through a middle small hole of a second off-axis parabolic mirror (13), and absorbs 1064nm pump light beams in a light path through a near infrared narrow-band filter (14), and finally the signal light is detected by a near infrared spectrometer (15) to have the radiation wavelength and is detected by a near infrared detector (16) to have the radiation power; the vacuum chamber (17) is adopted, so that the interference of water vapor in the air on terahertz absorption is avoided.
2. The system for detecting the terahertz difference frequency source for laser up-conversion according to claim 1, wherein the system comprises: the first nonlinear optical crystal (7) and the second nonlinear optical crystal (12) adopt inorganic crystals of gallium selenide, gallium phosphide, zinc germanium phosphide, cadmium telluride or lithium niobate, or organic nonlinear crystals of OH1, DAST or DSTMS.
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| CN110743104B (en) * | 2019-10-28 | 2023-03-17 | 鲍玉珍 | Terahertz wave physiotherapy terminal and terahertz wave physiotherapy system for cervical cancer |
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