CN106707288B

CN106707288B - Terahertz difference frequency source remote active detection system

Info

Publication number: CN106707288B
Application number: CN201710037294.9A
Authority: CN
Inventors: 黄志明; 黄敬国; 张娟; 杨秋杰; 李高芳; 周炜; 曲越; 姚娘娟; 张飞; 褚君浩
Original assignee: Shanghai Institute of Technical Physics of CAS
Current assignee: Shanghai Institute of Technical Physics of CAS
Priority date: 2017-01-19
Filing date: 2017-01-19
Publication date: 2023-07-04
Anticipated expiration: 2037-01-19
Also published as: CN106707288A

Abstract

The invention discloses a terahertz difference frequency source remote active detection system which comprises a high-power 1064nm laser, an optical parametric oscillator, a beam delay line, a half-wave plate, a polarization beam splitter prism, gallium selenide crystals, a terahertz lens, a terahertz reflector and a terahertz detector. The terahertz reflection/scattering signal active detection of the remote target is realized by utilizing the high-power terahertz difference frequency source radiation technology and combining the terahertz lens group quasi-parallel emission-echo focusing technology. The invention has the advantages of wide coverage wave band, good frequency band compatibility, simple structure, high system signal-to-noise ratio, long detection distance, room temperature operation and the like.

Description

Terahertz difference frequency source remote active detection system

Technical Field

The invention discloses a terahertz difference frequency source remote active detection system which utilizes a high-power optical terahertz difference frequency radiation source and a lens group quasi-optical means to realize remote target terahertz active detection.

Background

Terahertz waves, which are electromagnetic spectrum resources currently not fully developed by human beings, have unique spectrum characteristics, unlike infrared rays and millimeter waves, and are particularly low in photon energy and safe; the bandwidth is large, and the high-capacity high-definition real-time communication is convenient; the penetrability of the electrodeless molecules can be used for terahertz perspective imaging; the fingerprint absorption characteristic of a plurality of substances can be used for calibrating the composition of the substances. Terahertz technology has become one of the key technologies very important in the twenty-first century, and has very wide application background and scientific research value.

However, a huge obstacle is faced in the practical application process of the terahertz technology (the water vapor in the air has strong absorption characteristics on terahertz waves), which puts higher demands on various performance indexes (such as miniaturization, high power, narrow linewidth, continuous tunability and the like) of the terahertz radiation source in practical use. At present, research on high-power terahertz radiation sources has been the focus of research on terahertz science. Terahertz radiation sources are largely divided into two main categories, namely electronic sources and photonic sources, according to the manner in which they are generated: the electron source mainly comprises a free electron laser, a return wave tube, an electron frequency doubling source, a quantum cascade laser and the like; the photonics source mainly comprises a terahertz difference frequency source, a terahertz time-domain spectroscopy system, a terahertz mixing source, a terahertz gas laser and the like.

Compared with microwave and radio radars, the terahertz radar has the characteristics of good directivity, stealth detection prevention, large depth of field, high-definition rapid transmission and the like, and has extremely high military and civil application values. Regarding the terahertz remote detection technology, at present, the technology is basically still in an initial research stage, mainly adopts an electronic frequency multiplication terahertz radiation source as an active emission source (such as an MMAOP architecture applicable to terahertz radars and communication systems, patent number: CN201410094418.3, a ground terahertz radar system for cloud measurement, application number: CN 201510040930.4), but the effective working frequency band of the terahertz radiation source is limited to a low-frequency range (below 1 THz) and cannot be extended to a high-frequency range (above 1 THz).

Among the known terahertz radiation sources, the terahertz difference frequency source has the advantages of moderate volume, high radiation power (especially more than 1THz frequency band), narrow linewidth (GHz magnitude), large tuning range (0.1 THz-4 THz), continuous tuning, room temperature working and the like, and is considered to be an ideal light source for terahertz practical application.

The invention takes a high-power terahertz difference frequency source as an active emission source to conduct terahertz remote active detection system research, is an important research direction in the application of a remote terahertz technology, and can be widely applied to the important fields of terahertz active imaging, terahertz remote sensing, terahertz radar, terahertz security inspection and the like.

Disclosure of Invention

According to the terahertz differential frequency source active detection system, the terahertz differential frequency source active detection system is researched, and terahertz active detection of a target with high signal-to-noise ratio and long distance is realized by using a terahertz lens group quasi-optical means on the basis of high-power terahertz optical differential frequency radiation source research. Because the terahertz optical difference frequency source has high radiation power and small divergence angle, the system has very high target detection signal-to-noise ratio and longer target detection distance capability; meanwhile, the terahertz difference frequency source has a very wide spectrum radiation range, and meanwhile, the system has good spectrum compatibility, so that the terahertz difference frequency source is basically suitable for the requirement of remote target detection of the whole terahertz frequency band.

The specific contents are as follows: YAG laser and optical parametric oscillator with tunable wavelength of narrow linewidth are respectively derived from the Q Nd of 1064nm ns pulse modulation of narrow linewidth by using two terahertz difference frequency pump light, and the two pump light beams are arranged and combined through a series of optical elements (beam delay line, half wave plate and polarization coupling prism) to form a beam, and the laser of the combined beam is completely overlapped in space and time, and finally vertically incident into gallium selenide crystal to generate high-power terahertz light radiation. After the terahertz light is acted by the terahertz lens group of the transmitting light path, the terahertz light becomes quasi-parallel light (smaller beam divergence angle) to irradiate on a remote target, the reflected and scattered light on the surface of the target returns from a reverse light path, the direction of the reflected and scattered light is changed through the terahertz light reflecting mirror, and finally, the reflected and scattered light is focused into the terahertz detector by the terahertz lens group, so that the terahertz signal of the target is actively detected remotely.

The invention has the advantages of wide working frequency band (covering the whole terahertz frequency band of 0.1 THz-4 THz), simple structure, high signal-to-noise ratio, long detection distance, good frequency band compatibility, room temperature working and the like, is the core of application fields of remote terahertz radar monitoring, terahertz to-ground remote sensing, terahertz communication and the like, and can promote the development of the application fields of terahertz.

Drawings

Fig. 1 is a schematic diagram of a terahertz difference frequency source remote active detection system. In the figure, a 1064nm laser is shown in FIG. 1; 2 is a first half wave plate; 3 is an optical parametric oscillator; 4 is a beam delay line; 5 is a second half-wave plate; 6 is a polarization coupling prism; 7 is a near infrared lens; 8 is gallium selenide crystal; 9 is a near infrared filter; 10 is a first terahertz lens; 11 is a terahertz reflector; 12 is a second terahertz lens; 13 as a target; 14 is a third terahertz lens; 15 is a terahertz detector.

Detailed Description

The terahertz difference frequency source remote active detection system is specifically implemented and described by combining the attached drawings of the specification as follows:

the invention uses a 1064nm laser 1 as a main pump source of a terahertz difference frequency source, in particular to a pulse-modulated Q Nd-YAG laser, the working frequency is 10Hz, the pulse width is 8ns, and the line width is 0.003cm ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The other beam of pumping light adopts an optical parametric oscillator 3 generated by exciting the tripling frequency beam pumped by the 1064nm laser, has a wide-band wavelength tuning range (400-1700 nm), and has continuously adjustable radiation wavelength, pulse width of 4ns and narrow linewidth (linewidth of 0.075 cm) ^-1 ) And high radiation power (about 1070nm up to 150 mW). After the 1064nm pump beam passes through the first half wave plate 2, vertically polarized normal incidence is carried out on the pump beam to the polarization coupling prism 6; the output beam of the optical parametric oscillator 3 (such as 1070nm wavelength laser) is vertically incident into the polarization coupling prism 6 after passing through the beam delay line 4 and the second half-wave plate 5. The beam delay line 4 is adjusted to ensure that the two near infrared pump lasers are completely overlapped in the beam propagation space and time, and a collinear state is achieved. The combined pump light is focused to selenization through a near infrared lens 7In the gallium crystal 8, the terahertz radiation with high power and wide tuning wave band is realized under the nonlinear difference frequency effect by adjusting the phase matching angle of the crystal, and the rest near infrared pumping light beams in the light path are absorbed and filtered by the near infrared filter 9. The terahertz light is focused to the central small hole of the terahertz reflector 11 through the first terahertz lens 10, then is changed into quasi-parallel light beams (smaller beam divergence angle) through the second terahertz lens 12 to irradiate into the remote target 13, and the terahertz light signals reflected/scattered back through the surface of the target 13 are focused to the terahertz detector 15 through the third terahertz lens 14 after the reverse light path is changed in direction through the second terahertz lens 12 and the terahertz reflector 11, finally are converted into terahertz electric signals, and are displayed by related electronic detection instruments (such as a lock-in amplifier, a high-speed oscilloscope and the like).

It should be noted that the first terahertz lens 10 and the second terahertz lens 12 are used as terahertz emission light path collimating lens groups in the present system, and it is necessary to ensure that the focal position of the first terahertz lens 10 is located exactly at the focal position of the second terahertz lens 12 in actual operation; meanwhile, the second terahertz lens 12 and the third terahertz lens 14 serve as terahertz return light path focusing lens groups, and return light path terahertz light signals are further focused into the terahertz detector 15, so that long-distance detection of the whole system is realized.

The function of the optical elements in the system is described as follows:

1 is a high-power 1064nm laser, and provides a near-infrared pumping source required by a terahertz difference frequency source;

2 is a first half wave plate, and the polarization direction of 1064nm pump light is changed to enable the pump light to be vertically polarized;

3 is an optical parametric oscillator, which provides another wavelength pumping beam required by a high-power terahertz difference frequency source;

4 is a beam delay line, which is formed by a beam reflection delay light path formed by 4 near infrared laser high-reflection mirrors, and the delay time is about 4ns;

5 is a second half wave plate, which changes the polarization direction of the pump light emitted by the optical parametric oscillator to horizontally polarize the pump light;

a polarization coupling prism for coupling the 1064nm light beam and the output light beam of the optical parametric oscillator into a beam of light in a propagation space;

7 is a near infrared lens, which focuses the two near infrared pump beam combination light into the gallium selenide crystal;

8 is gallium selenide crystal, which can realize high power, narrow linewidth and continuously tunable terahertz difference frequency radiation under the effect of two near infrared pump light difference frequencies.

9 is a near infrared filter, which absorbs and filters the two residual near infrared lights in the light path and only transmits terahertz lights;

10 is a first terahertz lens, which focuses terahertz light in an optical path to a center aperture of a terahertz reflector;

11 is a terahertz reflector, and a small hole is formed in the center of the terahertz reflector, so that terahertz light in an emission light path can conveniently pass through the terahertz reflector, and terahertz light signals reflected and scattered by the surface of a target are reflected to a terahertz detector;

12 is a second terahertz lens, so that terahertz light beams in the transmitting light path are quasi-parallel to propagate, and terahertz light signals in the return light path are also conveniently collected;

13 is a target, and terahertz remote target detection is carried out;

14 is a third terahertz lens, and further collects terahertz signals in the return light path to focus the terahertz signals into a terahertz detector;

15 is a terahertz detector, which performs terahertz detection, in particular to a schottky terahertz detector with rapid response at room temperature.

Claims

1. The utility model provides a terahertz difference frequency source remote initiative detecting system, including 1064nm laser instrument (1), first half-wave plate (2), optical parametric oscillator (3), light beam delay line (4), second half-wave plate (5), polarization coupling prism (6), near infrared lens (7), gallium selenide crystal (8), near infrared filter (9), first terahertz lens (10), terahertz speculum (11), second terahertz lens (12), target (13), third terahertz lens (14) and terahertz detector (15), its characterized in that:

the laser emitted by the 1064nm laser (1) enters the polarization coupling prism (6) through the first half-wave plate (2), the optical parametric oscillator (3) emits near-infrared pump light with another wavelength, and the laser is incident into the polarization coupling prism (6) through the beam delay line (4) and the second half-wave plate (5), so that the two near-infrared pump light beams are completely overlapped in propagation time and space; the combined near-infrared pump light is focused into a gallium selenide crystal (8) through a near-infrared lens (7), so that high-power, narrow-linewidth and continuously tunable terahertz radiation is realized; the rest near-infrared pumping light beam in the light path is filtered and absorbed by a near-infrared filter (9), terahertz light is focused to a central small hole of a terahertz reflector (11) through a first terahertz lens (10), and is emitted to a remote target (13) in a quasi-parallel manner through a second terahertz lens (12); the terahertz optical signals reflected and scattered by the target surface are focused into a terahertz detector (15) through a second terahertz lens (12), a terahertz reflecting mirror (11) and a third terahertz lens (14) in sequence.