CN106645082B - Gated Fiber Raman Spectrometer Based on Laser Ranging and Autofocus - Google Patents

Abstract

The invention discloses a gated optical fiber Raman spectrometer based on laser ranging and automatic focusing, comprising a laser detection system, a Raman scattered light collection system, a signal trigger delay and a data processing control system; the optical fiber Raman spectrometer consists of a pulse A laser, a circulator, a first collimator, a reflecting prism, a dichroic prism, a photodetector telephoto lens system, a second collimator, an optical filter and a gated spectrometer are composed. The invention can realize direct and fast detection within a certain distance; the photoelectric detector can automatically determine whether the laser spot is irradiated on the object to realize automatic delay control; the electric control focusing device of the telephoto lens system can quickly realize automatic focusing; Optical fiber transmission is adopted, which greatly improves the mechanical stability and reliability of the equipment.

Description

Gated Fiber Raman Spectrometer Based on Laser Ranging and Autofocus

technical field

The invention relates to the technical field of spectrum measurement, in particular to a gated optical fiber Raman spectrometer based on laser ranging and automatic focusing.

Background technique

Raman line was first discovered by Indian physicist Raman in 1928 while studying the scattering of liquid benzene, and it is a kind of scattering spectrum. When light is irradiated on an object, some light will undergo inelastic scattering. In addition to the same elastic component (Rayleigh scattering) as the incident light, the scattered light also has components whose frequency increases and decreases compared to the incident light. The decreasing component is called the Stokes line, and the component with increasing frequency is called the anti-Stokes line, and the two components are symmetrically distributed on both sides of the excitation light frequency.

Raman effect This is mainly the result of molecular vibrations, optical phonons in the lattice interacting with the excitation light source. When a photon interacts with a molecule, the molecule absorbs a photon and enters an unstable virtual energy state, and then quickly emits a photon. At this time, if the vibration or rotation energy level of the molecule is higher than the initial energy level , then the frequency of the emitted photon will be lower than the original photon, which is called Stokes light. On the contrary, the vibration or rotation energy level of the molecule is lower than the initial one, the energy of the photon will increase, and the frequency will increase, which is called anti-Stokes light. The regular changes in photon frequency recorded by Raman spectrometer are called Raman spectroscopy.

Currently, these spectrometers require the sample to be placed in a set-up sample chamber, or the probe needs to be placed next to the sample in order to collect sufficiently strong Raman scattered light. This close-fitting measurement greatly limits the use of the device. For example, the Raman spectrometer cannot obtain the mineral composition of a certain area as quickly as the infrared imaging spectrometer. In addition, if the Raman spectrometer is used on the alien lander or rover to analyze the material composition of the planet's surface, an additional manipulator is required to place the sample on the In the sample room, the difficulty of operation is increased.

SUMMARY OF THE INVENTION

The present invention provides a gated optical fiber Raman spectrometer based on laser ranging and automatic focusing. The purpose is to improve the utilization rate of the Raman spectrometer and the signal-to-noise ratio by using the long-distance Raman spectrometer, so as to realize long-distance non-sampling detection. .

The technical scheme of the present invention is: a gated optical fiber Raman spectrometer based on laser ranging and automatic focusing, comprising a laser detection system, a Raman scattered light collection system and a signal trigger delay and data processing control system.

The laser detection system includes a laser emission detection system and a laser reflection detection system.

The laser emission detection system includes a pulsed laser, a circulator, a first collimator, a reflection prism and a dichroic prism.

The laser reflection system is an inverse system of the laser emission system, and the laser reflection system includes the pulse laser, a circulator, a first collimator, a reflection prism, a dichroic prism, and a photodetector.

The Raman scattered light collection system includes the dichroic prism, a telescopic lens system, a second collimator, an optical filter and a gated spectrometer.

Preferably, the circulator is a three-port circulator, and the optical fiber is a special single-mode optical fiber with optimized design with little loss to visible light.

The pulsed laser and the first collimator are respectively connected with the circulator through an optical fiber. The reflecting prism and the first collimator are placed along the optical path in the reflection direction of the dichroic prism. The collimators are placed relatively parallel.

The sample, the telescopic lens system, the optical filter and the second collimator are placed in the transmission direction of the dichroic dichroic prism in sequence along the optical path; the gated spectrometer is connected with the second collimator through an optical fiber.

The pulsed laser is provided with a laser pulse trigger, the photodetector is connected to the circulator through an optical fiber, the telephoto lens system is provided with an electronically controlled focusing device, the laser pulse trigger and the photodetector are , the electronically controlled focusing device and the gated spectrometer are respectively connected with the data processing control system through a serial bus.

Preferably, the gated spectrometer may be a fiber-gated spectrometer based on a fiber F-P tunable filter sweep, a gated spectrometer based on grating dispersion, or a gated spectrometer based on spatial Fourier transform.

Preferably, the reflecting prism and the dichroic prism can be installed separately or in combination to realize reflection or transmission of the laser beam.

Preferably, the dichroic prism can be a specially-made coated prism, or an assembled beam splitting system; the reflective prism is a high-reflection mirror with a surface coating of 99%, and the reflective prism is a primary, etc. Waist right angle prism.

A ranging method for a gated optical fiber Raman spectrometer based on laser ranging and automatic focusing, the method comprises the following steps:

1) The pulsed laser emits ns-level pulsed laser, which passes through the first collimator and the reflecting prism in sequence through the circulator, and at the same time the pulsed laser emits a triggering electrical signal;

2) The laser beam enters the dichroic prism after being reflected by the reflective prism, and then is reflected again through the dichroic prism, and the propagation direction of the laser beam is parallel to the laser beam emitted by the first collimator;

3) When the laser beam reaches the surface of the sample, reflection and scattering occur. Part of the Rayleigh scattered light and reflected light will enter the circulator along the original optical path, and will be detected by the photodetector through the circulator. If the reflected light cannot be detected by the detector, it means that the pulsed laser The light spot is not aligned with the surface of the object to be measured, and the direction of the device needs to be adjusted; if reflected light is detected, the data processing system records the time it reaches the photodetector, and then compares it with the time of the trigger signal to turn on the gated spectrometer. The delayed reference signal of , starts the gated spectrometer when the next laser pulse is generated;

4) Part of the Raman scattered light is transmitted through the dichroic prism into the telescopic lens system, collected by the front-end objective lens and collected by the rear-end objective lens to the filter, and the filter removes part of the Rayleigh scattered light and reflected light, leaving the Raman scattered light The light is concentrated to the second collimator and transmitted to the gated spectrometer through the optical fiber;

5) Calculate the distance between the object to be measured and the gated spectrometer by using the delay time, so as to adjust the position of the lens in the telephoto lens system and realize the automatic focusing function;

6) The opening of the gated spectrometer is determined by the delay time in step 3), and the opening time is determined by the pulse width of the pulsed laser;

7) After the readout signal of the spectrometer is processed and sorted by the data processing control system, it is judged whether more pulse signals are needed.

The optical path of the laser emission detection system is that the laser beam enters the first collimator, converts the laser light into parallel light and enters a primary isosceles right-angle reflecting prism, which is reflected by the reflecting prism and enters the dichroic prism. The beam is rotated 90° counterclockwise in parallel with the laser beam emitted by the first collimator, and the laser beam emitted by the dichroic prism reaches the sample.

The beneficial effects of the invention are as follows: the gated optical fiber Raman spectrometer based on laser ranging and automatic focusing does not need sampling, and can realize direct and rapid detection within a certain distance; whether the laser spot irradiates the object can be automatically judged by the photodetector Automatic time delay control is realized on the telephoto lens system; automatic focusing is quickly realized through the electronically controlled focusing device of the telephoto lens system; the coaxial system is adopted to ensure that the light entering the telephoto lens system for imaging is emitted from the sample irradiated by the laser, It avoids the situation that the scattered light cannot be collected correctly due to the inconsistent laser light path and the collection light path; at the same time, optical fiber transmission is adopted, which greatly improves the mechanical stability and reliability of the equipment.

Description of drawings

Further objects, functions and advantages of the present invention will be elucidated by the following description of embodiments of the present invention with reference to the accompanying drawings, wherein:

1 shows a schematic structural diagram of a gated optical fiber Raman spectrometer based on laser ranging and auto-focusing of the present invention;

FIG. 2 shows a schematic structural diagram of Embodiment 2 of the gated optical fiber Raman spectrometer based on laser ranging and automatic focusing according to the present invention.

Detailed ways

Objects and functions of the present invention and methods for achieving these objects and functions will be elucidated by referring to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it may be implemented in various forms. The essence of the description is merely to assist those skilled in the relevant art to comprehensively understand the specific details of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numbers represent the same or similar parts, or the same or similar steps.

FIG. 1 is a schematic structural diagram of a gated optical fiber Raman spectrometer based on laser ranging and automatic focusing according to the present invention. As shown in FIG. 1, the gated fiber Raman spectrometer based on laser ranging and automatic focusing includes a pulsed laser 101, a laser pulse trigger 102, a circulator 103, a first collimator 104, a reflecting prism 105, a dichroic separation Prism 106 , sample 107 , telescopic lens system 108 , filter 109 , second collimator 115 , gated spectrometer 110 , data processing system 111 , photodetector 112 , optical fiber 113 and electronically controlled focusing device 114 .

The circulator 103 is a three-port circulator, and the pulsed laser 101 , the first collimator 104 and the photodetector 112 are respectively connected to port 1 , port 2 and port 3 of the circulator 103 through optical fibers.

The front end of the telescopic lens system 108 is used for collecting scattered light, and the rear end is used for collecting scattered light. The telescopic lens system 108 can be realized by connecting a lens matching the speed of light at the rear end of the telescope.

The pulse laser 101 is provided with a laser pulse trigger 102, and the rear end of the telephoto lens system 108 is provided with an electronically controlled focusing device 114. The laser pulse trigger 102, the electronically controlled focusing device 114, the photodetector 112 and the The gated spectrometer 110 is connected to the data processing system via a serial bus.

The optical fiber is a special single-mode optical fiber with optimized design with low visible light loss.

The sample, the telescopic lens system, the filter and the second collimator are placed in the transmission direction of the dichroic dichroic prism along the optical path in sequence; the reflecting prism and the first collimator are placed in the dichroic direction along the optical path in sequence The direction of reflection of the dichroic prism.

The gated spectrometer may be a fiber-gated spectrometer based on a fiber F-P tunable filter sweep, a gated spectrometer based on grating dispersion, or a gated spectrometer based on spatial Fourier transform.

The dichroic prism can be a special coating prism or an assembled beam splitting system; the reflecting prism is a high reflectance mirror with a surface coating of 99%, and the reflecting prism is a primary isosceles right angle prism .

Example 1

A gated optical fiber Raman spectrometer based on laser ranging and automatic focusing includes a laser detection system, a Raman scattered light collection system, a signal trigger delay and a data processing control system.

Laser detection systems are divided into laser emission detection systems and laser emission detection systems.

The laser emission detection system consists of a pulsed laser 101, a circulator 103, a first collimator 104, a reflection prism 105, a dichroic prism 106 and a sample 107; the pulsed laser 101 emits a ns-level laser beam, which enters the circulator 103 port 1. The laser beam at port 2 of the circulator 103 enters the first collimator 104 to turn the laser beam into parallel light and enters the reflective prism 105. After passing through the reflective prism 105, the propagation direction of the laser beam rotates 90° clockwise and enters the dichroic dichroic prism 106 , the propagation direction of the laser beam through the dichroic prism 106 is rotated 90° counterclockwise, parallel to the same direction as the laser beam emitted by the first collimator 104 , and the laser beam emitted by the dichroic prism 106 reaches the sample 107 .

The laser reflection detection system is composed of a sample 107, a dichroic dichroic prism 106, a reflecting prism 105, a first collimator 104, a circulator 103 and a photodetector 112; Rayleigh scattered and reflected light will return along the original light path. Part of the Rayleigh scattered light and reflected light reaches the port 2 of the circulator 103 along the dichroic dichroic prism 106, the reflecting prism 105 and the first collimator 104, and the laser light at the port 3 of the circulator 103 is connected to the port 3 of the circulator 103 The photodetector 112 detects.

The Raman scattered light collection system is composed of a sample 107, a dichroic prism 106, a telephoto lens system 108, a filter 109, a second collimator 115 and a gated spectrometer 110; the Raman scattered light emitted by the sample 107 passes through The dichroic prism 106 transmits and reaches the telescopic lens system 108, and is collected by the front-end objective lens and the rear-end objective lens of the telescopic lens system 108, and the laser beam is converged to the second collimator 115, and is placed in the second collimator 115 and the telescope. The filter 109 between the far transmission systems 108 removes the Rayleigh scattered light and reflected laser light, and the remaining Raman scattered light is transmitted to the gated spectrometer 110 through the optical fiber 113 .

The pulsed laser 101 used in this embodiment is a Q-switched pulsed Nd:YAG laser, and after frequency doubling, a laser with a wavelength of 532 nm is obtained, the pulse width is 8-10 ns, the single pulse energy is 20-100 mJ, and the repetition frequency is 10-100 Hz; The reflection prism 105 is a primary isosceles right angle prism.

In this embodiment, a method for a gated optical fiber Raman spectrometer based on laser ranging and automatic focusing, wherein the specific testing method includes the following steps:

1) The solid Nd:YAG laser 101 emits a pulsed laser with a pulse width of 8-10ns under the active electro-optical modulation Q-switching, the laser wavelength is 532nm, and the frequency is 10Hz. Signal;

2) The laser pulse is coupled to the port 1 on the circulator 103 through the optical fiber, and is output through the port 2 of the circulator 103 to reach the first collimator 104 through the optical fiber;

3) After the laser pulse emits parallel light from the first collimator 104, a space optical path is formed, reaching the primary isosceles right angle prism 105, and the optical path is rotated 90° clockwise;

4) The laser pulse reaches the dichroic prism 106, and the dichroic prism reflects light with a wavelength less than 535 nm, and transmits light with a wavelength greater than 535 nm, so the laser pulse reaches the dichroic prism 106 and then reflects, and the optical path is reversed at this time. When the hour hand rotates 90°, the direction of the optical path is parallel to and in the same direction as the original direction.

5) When the laser pulse irradiates the sample 107, the laser light will be scattered and reflected on the surface, and a part of the scattered light and reflected light will return to the dichroic prism 106 through the original path, where the Rayleigh scattered light and reflected light are due to their wavelengths. The wavelength less than 535nm will be reflected by the dichroic prism 106 and enter the primary isosceles right angle prism 105 ; and the Raman scattered light will enter the telephoto lens system 108 after passing through the dichroic prism 106 because its wavelength is greater than 535nm.

6) Rayleigh scattered light and reflected light are collected by the first collimator 104 after being reflected by the primary isosceles right angle prism 105, coupled into the optical fiber and then reach the port 2 of the circulator 103, and the light is detected by the photodetector 112 after passing through the port 3 . When the signal strength exceeds a certain value, it can be used to start the gated spectrometer 110. In addition, the time difference between the arrival time of the reflected light and the pulse electrical signal sent by the laser pulse trigger 102 can be used as a reference delay time, indicating that a period of time has elapsed after the laser pulse is sent. The gated spectrometer 110 starts to respond after a delay, so that the signal light can be fully received and the accumulation and absorption of the background light can be avoided.

7) Using the delay time to realize ranging, and the data control system 111 and the electronically controlled focusing device 114 automatically adjust the focus of the lens in the telephoto lens system 108 .

8) After the Raman scattered light reaches the dichroic prism 106, it will be transmitted into the telephoto lens system 108, collected by the front-end high-power objective lens, and then converged into parallel light by the rear-end objective lens, and the reflected light and Rayleigh scattering are filtered out by the filter 109. After the light, it enters the second collimator 115 and enters the gated spectrometer 110 through the optical fiber 113 .

9) The gated spectrometer 110 is always in a closed state when there is no start-up signal, only the detection signal generated by the reflected light in step 6) can be used to start the spectrometer, and the CCD in the spectrometer starts to receive the signal when the Raman scattered light arrives, The turn-on time of the spectrometer is determined by the laser pulse width, which is set to 10 ns.

10) The spectrum read from the spectrometer will be fed back to the data processing control system 111, and its signal-to-noise ratio will be obtained through calculation. If the signal-to-noise ratio is too low, further instructions for detection will be issued, and the pulsed laser 101 will continue to emit pulses. After the same delay time, start the CCD to receive the signal, and then the data processing control system fuses this data with the previously obtained data to obtain a new signal-to-noise ratio, and so on until the signal-to-noise ratio exceeds the predetermined value. Finally, the data processing control system issues an instruction to turn off the laser and the spectrometer.

Example 2

FIG. 2 is a schematic structural diagram of Embodiment 2 of a gated optical fiber Raman spectrometer based on laser ranging and automatic focusing according to the present invention. The difference between this embodiment and Embodiment 1 is that the reflective prism 105 and the dichroic prism 106 are changed. As shown in FIG. 2 , in this embodiment, the included angle between the reflection prism and the first collimator is 45°, and the dichroic dichroic prism is placed in parallel with the reflection prism in the longitudinal direction.

The positional relationship of the prism group 201 can also be that the angle between the reflection prism and the first collimator is 45°, and the dichroic prism is placed vertically relative to the reflection prism in the longitudinal direction; the reflection prism and the dichroic prism can be placed separately It can also be installed in combination with two sets of prisms to realize the reflection or transmission of the laser beam.

Other embodiments of the present invention will be readily apparent to and understood by those skilled in the art in conjunction with the specification and practice of the present invention disclosed herein. The description and examples are to be regarded as exemplary only, with the true scope and spirit of the invention being defined by the claims.

Claims (6)

1. a ranging method based on the gated optical fiber Raman spectrometer of laser ranging auto-focusing, it is characterized in that, the gated optical fiber Raman spectrometer based on laser ranging auto-focusing comprises laser detection system, Raman scattered light Collection system and signal trigger delay and data processing control system; The laser detection system includes a laser emission detection system and a laser reflection detection system; The laser emission detection system includes a pulsed laser, a circulator, a first collimator, a reflection prism and a dichroic prism; The laser reflection system is an inverse system of the laser emission system, and the laser reflection system includes the pulsed laser, a circulator, a first collimator, a reflection prism and a photodetector; The Raman scattered light collection system includes the dichroic prism, a telephoto lens system, a second collimator, an optical filter and a gated spectrometer; The pulsed laser and the first collimator are respectively connected with the circulator through an optical fiber, and the reflection prism and the first collimator are placed along the optical path in the reflection direction of the dichroic prism; The telescopic lens system, the optical filter and the second collimator are sequentially placed in the transmission direction of the dichroic dichroic prism along the optical path; the gated spectrometer is connected with the second collimator through an optical fiber; The pulsed laser is provided with a laser pulse trigger, the photodetector is connected with the circulator through an optical fiber, and the telescopic lens system is provided with an electronically controlled focusing device; The laser pulse trigger, photodetector, electronically controlled focusing device and gated spectrometer are respectively connected with the data processing control system through a serial bus; The method includes the following steps: 1) The pulsed laser emits ns-level pulsed laser, which passes through the first collimator and the reflecting prism in sequence through the circulator, and at the same time the pulsed laser emits a triggering electrical signal; 2) The laser beam is reflected by the reflective prism into the dichroic prism, and then reflected again by the dichroic prism, and the propagation direction of the laser beam is parallel and in the same direction as the laser beam emitted by the first collimator; 3) When the laser beam reaches the sample surface, it is reflected and scattered. Part of the Rayleigh scattered light and reflected light will enter the circulator along the original optical path, and will be detected by the photodetector through the circulator. If the detector cannot detect the reflected light, the direction of the device will be affected. Adjustment; if the reflected light is detected, the data processing system records the time of reaching the photodetector, and then compares it with the time of the trigger signal to obtain a delay reference signal for opening the gated spectrometer, and starts the gated control when the next laser pulse is generated. spectrometer; 4) Part of the Raman scattered light is transmitted through the dichroic prism into the telescopic lens system, collected by the front-end objective lens and collected by the rear-end objective lens to the filter, and the filter removes part of the Rayleigh scattered light and reflected light, leaving the Raman scattered light The light is concentrated to the second collimator and transmitted to the gated spectrometer through the optical fiber; 5) Calculate the distance between the object to be measured and the gated spectrometer by using the delay time, and adjust the position of the lens in the telephoto lens system by the data control system and the electronically controlled focusing device to realize automatic focusing; 6) The opening of the gated spectrometer is determined by the delay time in step 3), and the opening time is determined by the pulse width of the pulsed laser; 7) After the readout signal of the gated spectrometer is processed and sorted by the data processing control system, it is judged whether more pulse signals are needed. 2. a kind of ranging method based on the gated optical fiber Raman spectrometer of laser ranging automatic focusing according to claim 1, is characterized in that, described circulator is a three-port circulator, and described optical fiber is single-mode fiber. 3 . The ranging method for a gated fiber Raman spectrometer based on laser ranging and auto-focusing according to claim 1 , wherein the reflecting prism and the first collimator are relatively parallel to each other. 4 . 4. a kind of ranging method based on the gated optical fiber Raman spectrometer of laser ranging automatic focusing according to claim 1, is characterized in that, described gated spectrometer can be based on optical fiber F-P tunable filter sweep surface fiber-gated spectrometers, or gated spectrometers based on grating dispersion, or gated spectrometers based on spatial Fourier transform. 5. a kind of ranging method based on the gated optical fiber Raman spectrometer of laser ranging automatic focusing according to claim 1, is characterized in that, described dichroic prism can be a special coating prism, It can also be an assembled light-splitting system; the reflecting prism is a primary isosceles right-angle prism with a surface coating of 99%. 6. a kind of ranging method based on the gated optical fiber Raman spectrometer of laser ranging auto-focusing according to claim 1, is characterized in that, described reflecting prism and dichroic prism can be installed separately also can A combination of the two is installed.

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