Laser-induced Raman and fluorescence spectrum testing system

Abstract

The invention discloses a laser-induced Raman and fluorescence spectrum testing system, which relates to the technical field of spectrum testing and comprises a laser module, a harmonic separation mirror, a frequency doubling crystal, a first cavity mirror, a sample pool, a second cavity mirror and a spectrum detection unit, laser output by the laser module sequentially passes through the harmonic separation mirror, the frequency doubling crystal and the first cavity mirror; a high-transmittance film and a high-reflection film are respectively plated on two surfaces of the harmonic separation mirror, and the harmonic separation mirror reflects the laser with the required wavelength to the sample cell; the second cavity mirror is used for turning back the laser from the sample cell; a harmonic separation mirror, a first cavity mirror, a second focusing lens and a second cavity mirror form a double-beam-waist laser resonant cavity. The first cavity mirror and the second cavity mirror are spherical reflectors and are respectively plated with high-reflection films. The first cavity mirror and the first focusing lens are confocal, and the second cavity mirror and the focusing lens are confocal. And two beam waist focuses of the laser resonant cavity are respectively arranged at the positions of the frequency doubling crystal and the sample pool, so that the optimal frequency doubling efficiency and sample excitation efficiency are realized.

Description

Technical Field

[0001] The invention relates to the technical field of spectrum testing, in particular to a laser induced Raman and fluorescence spectrum testing system. Background Art

[0002] With the continuous development of laser technology, the Raman and fluorescence detection technology and application scope using laser as excitation source are becoming more and more extensive. The detection objects in practical applications are diverse, and solids, liquids and gases can all use laser as excitation source to detect Raman and fluorescence signals.

[0003] Conventional Raman and fluorescence detection systems mostly use a point excitation and point collection test method. That is, the laser is focused on the sample to be tested, and then the fluorescence or scattering (Raman, Rayleigh) signal generated by the laser point on the sample is collected through the collection optical path to the spectral signal measurement device for detection. The existing laser excitation Raman and fluorescence spectrum test system, the excitation and collection optical path is suitable for non-transparent samples such as solid and powder samples, while for transparent substances such as gases and liquids, the absorption and scattering cross-sections of the excitation light are low, and the excited fluorescence or Raman signals are also weak. Especially for gas samples, it is necessary to improve the excitation efficiency through multiple reflections, increased pressure, etc.

[0004] In order to solve the above problems, the first existing technology uses hollow photonic crystal fiber to increase the Raman signal of gas: the excitation light is focused into the hollow photonic crystal fiber, and the gas to be measured is filled into the fiber at normal pressure or increased pressure. The laser is reflected multiple times in the fiber to achieve the excitation of the gas, and the generated Raman scattering signal is also reflected multiple times in the fiber, and then emitted through the fiber outlet and received by the collection lens for signal detection by the spectrum detector. Since the core diameter of the photonic crystal fiber is usually several microns, the laser is coupled to the fiber through a microscope objective lens, and a microscopic Raman optical system is usually used, which has high system cost and debugging difficulty; the laser coupling into the fiber is easy to cause ablation of the fiber mouth surface; the fiber cut needs to be re-cut frequently and the coupling optical path needs to be adjusted; the hollow photonic crystal fiber is not a conventional batch product, and can only be manufactured by individual research units, with high cost; it can only be used for gas detection, not for liquids; it can only collect and detect signal light that satisfies the total reflection of the fiber in the direction of laser transmission.

[0005] The second existing technology adopts a multi-return cavity method to increase the Raman signal: the multi-reflection cavity can effectively prolong the interaction time of the laser and the gas molecules by multiple reflections of the laser between the cavity mirrors, and realize signal detection by collecting the Raman or fluorescence spectrum signals generated by the interaction of the laser and the material in the same direction as the laser transmission; in this technical solution, the multi-return cavity has no gain and the reflectivity of the multi-return cavity mirror directly determines the number of reflections of the laser in the cavity. The gain efficiency can only be improved by increasing the laser power and reflectivity, and usually only a few dozen times of gain output can be achieved; the detection substance needs to fill the multi-return cavity, and the sample amount of the detection substance is relatively large; only signals in the same direction as the laser transmission optical path can be collected, and the signal collection efficiency is relatively low; it is usually only suitable for gas detection.

[0006] Prior art three uses a multi-return cavity method to increase the Raman signal: similar to prior art two, the laser passes through a confocal cavity, and the laser is reflected through the focus of the confocal cavity. Signal detection is achieved by collecting the spectrum generated by the interaction between the laser and the material at the focal position. Compared with prior art two, the confocal cavity collects the signal generated at the focus, and the required sample volume is relatively small; however, there is no gain in the cavity in this technical solution. The structure and reflectivity of the confocal cavity directly determine the number of reflections of the laser in the cavity. The gain efficiency can only be improved by increasing the laser power and reflectivity, and usually only a few dozen times of gain output can be achieved; only at the focus can the signal be enhanced by multiple reflections.

[0007] In view of this, a laser induced Raman and fluorescence spectroscopy testing system is urgently needed. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention solves the problems with the following technical structure.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A laser induced Raman and fluorescence spectrum testing system, comprising: a laser module, a harmonic separation mirror, a frequency doubling crystal, a first cavity mirror, a sample cell, a second cavity mirror and a spectrum detection unit;

[0011] The laser output from the laser module passes through the harmonic separation mirror, the frequency doubling crystal and the first cavity mirror in sequence;

[0012] The side of the harmonic separation mirror close to the laser module is coated with a high-transmittance film, and the side of the harmonic separation mirror close to the frequency doubling crystal is coated with a high-reflection film. The harmonic separation mirror separates the laser from the frequency doubling crystal and reflects the laser of the required wavelength to the sample pool;

[0013] The first cavity mirror is used to reflect the laser from the frequency doubling crystal back to the frequency doubling crystal;

[0014] The second cavity mirror is used to reflect the laser from the sample cell back to the sample cell;

[0015] The spectrum detection unit is used to analyze and detect the samples in the sample pool.

[0016] A further feature is that

[0017] The laser module comprises a pump laser, a wave plate and a first focusing lens. The laser outputted by the pump laser passes through the wave plate, the first focusing lens and the harmonic wave separation mirror in sequence.

[0018] A Faraday optical isolator is arranged between the pump laser and the wave plate.

[0019] The wave plate is a half wave plate.

[0020] A second focusing lens is arranged between the harmonic separation mirror and the sample cell.

[0021] It also includes a collecting reflector for collecting and reflecting the scattered or fluorescent signals generated by the sample, a collimating lens and a laser filter for collimating the scattered and fluorescent signals from the sample pool. The collimated laser passes through the laser filter and enters the spectral detection unit.

[0022] The system further comprises a third focusing lens, which focuses the laser light entering the spectrum detection unit.

[0023] The spectrum detection unit comprises a slit, a collimator, a spectrometer and a planar array detector, and the laser from the sample passes through the slit, the collimator, the spectrometer and the planar array detector in sequence.

[0024] The spectrum detection unit further includes a fourth focusing lens, which is arranged between the beam splitter and the area array detector.

[0025] The spectrum detection unit includes a linear array detector.

[0026] The above structure of the present invention can achieve the following beneficial effects:

[0027] The harmonic separation mirror, the first cavity mirror, the second focusing lens and the second cavity mirror form a double-waist laser resonant cavity. The first cavity mirror and the second cavity mirror are spherical reflectors, respectively coated with different high-reflection films. The first cavity mirror is confocal with the first focusing lens, and the second cavity mirror is confocal with the second focusing lens. The two beam waist foci of the laser resonant cavity are respectively at the frequency doubling crystal and the sample pool to achieve the best frequency doubling efficiency and sample excitation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present application;

[0029] Figure 2 This is a schematic diagram of the structure of the second embodiment of the present application;

[0030] Figure 3 This is a structural diagram of Example 3 of the present application.

[0031] In the figure: 1-1, pump laser; 1-2, Faraday optical isolator; 1-3, wave plate; 1-4, first focusing lens; 1-5, harmonic separation mirror; 1-6, frequency doubling crystal; 1-7a, first cavity mirror; 1-7b, second cavity mirror; 1-8, second focusing lens; 2-1, sample cell; 2-2, collecting reflector; 2-3, collimating lens; 2-4, laser filter; 2-5, third focusing lens; 3, spectral detection unit; 3-1-1, slit; 3-1-2, collimating mirror; 3-1-3, spectrometer; 3-1-4, fourth focusing mirror; 3-1-5, array detector. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0033] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product or equipment comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0034] The following is combined with Figure 1-3 This application is described in further detail.

[0035] Example 1, reference Figure 1A laser induced Raman and fluorescence spectrum testing system shown in the figure includes: a laser module, a harmonic separation mirror 1-5, a frequency doubling crystal 1-6, a first cavity mirror 1-7a, a sample pool 2-1, a second cavity mirror 1-7b and a spectrum detection unit 3; the laser output from the laser module passes through the harmonic separation mirror 1-5, the frequency doubling crystal 1-6 and the first cavity mirror 1-7a in sequence; the harmonic separation mirror 1-5 is coated with a high-transmittance film and a high-reflection film on both sides along the laser transmission direction (the direction from the laser module to the frequency doubling crystal 1-6), the harmonic separation mirror 1-5 separates the laser from the frequency doubling crystal, and reflects the laser of the required wavelength to the sample pool 2-1, the harmonic separation mirror 1-5 and A second focusing lens 1-8 is arranged between the sample pools 2-1; the first cavity mirror 1-7a is used to reflect the laser from the frequency doubling crystal back to the frequency doubling crystal 1-6; the second cavity mirror 1-7b is used to return the laser from the sample pool (reflect it back to the sample pool); the spectral detection unit 3 is used to analyze and detect the sample at the sample pool 2-1, wherein the laser module includes a pump laser 1-1, a Faraday optical isolator 1-2, a wave plate 1-3 and a first focusing lens 1-4, the laser output from the pump laser 1-1 passes through the Faraday optical isolator 1-2, the wave plate 1-3, the first focusing lens 1-4 and the harmonic wave separation mirror 1-5 in sequence, and the wave plate 1-3 is a half wave plate.

[0036] Based on the above structure, the output laser from the pump laser 1-1 passes through the Faraday optical isolator 1-2, the wave plate 1-3, the first focusing lens 1-4, the harmonic separation mirror 1-5, the frequency doubling crystal 1-6, and finally reaches the first cavity mirror 1-7a. When the laser reaches the frequency doubling crystal 1-6, the frequency doubling crystal 1-6 converts the laser into its doubled frequency light (converts the laser of a specific wavelength into a laser of half its wavelength), and then the laser reaches the first cavity mirror 1-7a, and the first cavity mirror 1-7a converts the wavelength after frequency doubling. The laser light and the remaining laser light of the original wavelength are reflected back to the frequency doubling crystal 1-6, and reach the harmonic separation mirror through the frequency doubling crystal. Then, since the harmonic separation mirror 1-5 is coated with a high-reflection film and a high-transmittance film, the frequency-doubled laser light is reflected to the sample pool 2-1, and the remaining laser light returns along the original route through the high-transmittance film. The second cavity mirror 1-7b is arranged on the opposite side of the harmonic separation mirror 1-5, and reflects the laser light from the sample pool 2-1 back to the sample pool 2-1, and returns the laser light, thereby completing the multiplication of the laser energy of the required wavelength.

[0037] like Figure 1As shown, this embodiment also includes a collecting reflector 2-2 for collecting and reflecting the scattered or fluorescent signals generated by the sample, a collimating lens 2-3 for collimating the scattered and fluorescent signals at the sample pool 2-1, a laser filter 2-4 and a third focusing lens 2-5. The collimated laser passes through the laser filter 2-4 and enters the spectrum detection unit 3. The third focusing lens 2-5 is used to focus the laser that is about to enter the spectrum detection unit. In this way, the laser reflected by the harmonic separation mirror 1-5 reaches the sample pool 2-1, and the scattered or fluorescent signals generated by the gas or liquid sample in the sample pool 2-1 after laser excitation Fluorescence signal, collecting reflector 2-2 and spectral detection unit 3 are arranged on the opposite side of sample pool 2-1, and the scattered or fluorescent signal generated by the sample at sample pool 2-1 is collected by collecting reflector 2-2 and reflected back to sample pool 2-1, and reaches collimating lens 2-3 together, so as to reduce the loss of scattering or fluorescent signal generated by laser excitation of gas or liquid sample in sample pool 2-1, and gain the laser of required wavelength, while sample pool 2-1 is collimated by collimating lens 2-3 and filtered by laser filter 2-4, and finally the signal light is focused into spectral detection unit 3 by third focusing lens 2-5.

[0038] The following is a detailed description of the 1064nm pump frequency-doubled output 532nm laser for excitation:

[0039] Wherein: the output laser of 1064nm laser 1-1 is focused to frequency doubling crystal 1-6 after passing through Faraday optical isolator 1-2, 1 / 4λ wave plate 1-3, first focusing lens 1-4 and harmonic separation mirror 1-5 to generate 532nm laser. Faraday optical isolator 1-2 is used to isolate the 1064nm laser reflected by the first cavity mirror 1-7a from entering the laser to avoid damage to the laser, wave plate 1-3 (a 1 / 4λ wave plate is selected in this embodiment) is used to adjust the polarization direction of the laser to achieve phase matching with frequency doubling crystal 1-6 to achieve the best frequency doubling efficiency, and the double sides of harmonic separation mirror 1-5 are respectively coated with 1064nm high-transmittance film and 532nm high-reflection film to achieve transmission of pump 1064nm laser and high reflection of frequency doubling 532nm laser. The 532nm laser generated by the 1064nm laser through the frequency doubling crystal 1-6 and the remaining 1064nm laser are reflected by the first cavity mirror 1-7a and then pass through the frequency doubling crystal 1-6. The harmonic separation mirror 1-5 separates the 532nm laser from the 1064nm laser, and the 1064nm laser returns to the laser 1-1 along the original path. The 532nm laser is reflected by the second focusing lens 1-8 and focused to the sample pool 2-1, and then reflected by the second cavity mirror 1-7b and returned along the original optical path. The harmonic separation mirror 1-5, the first cavity mirror 1-7a, the second focusing lens 1-8 and the second cavity mirror 1-7b form a double-waist 532nm laser resonant cavity. The first cavity mirror 1-7a and the second cavity mirror 1-7b are spherical reflectors, which are coated with 532nm and 1064nm high-reflection films respectively. The first cavity mirror 1-7a is confocal with the first focusing lens 1-4, and the second cavity mirror 1-7b is confocal with the second focusing lens 1-8. The two beam waist foci of the 532nm laser resonant cavity are located at the frequency doubling crystal 1-6 and the sample cell 2-1 respectively to achieve the best frequency doubling efficiency and sample excitation efficiency.

[0040] The above system structure can realize the power doubling of the 532nm laser generated by the crystal frequency doubling of the 1064nm laser in the resonant cavity, and the stability is achieved when the 532nm laser power in the cavity and the 532nm power generated by the frequency doubling of the 1064nm laser are the same as the intracavity loss. By increasing the 1064nm pump power and improving the frequency doubling efficiency, and controlling the intracavity loss (reflection and diffraction loss of the intracavity device and the absorption and scattering loss of the sample), the intracavity 532nm laser power can be doubled by an order of magnitude. Of course, here only 1064nm pump frequency doubling output 532nm laser is used as an example. This method can also achieve intracavity gain enhancement of other excitation wavelengths, such as pumping light of 1570nm and frequency doubling to achieve intracavity resonance of 785nm laser. The frequency doubling crystal can also be changed to a laser crystal such as a YAG crystal, and 808nm pumping can be used to achieve intracavity enhancement of 1064nm laser.

[0041] Embodiment 2, as Figure 2As shown, the spectrum detection unit includes a slit, a collimator, a spectrometer and a planar array detector. The laser from the sample passes through the slit, the collimator, the spectrometer, the fourth focusing lens and the planar array detector in sequence. The third focusing lens 2-5 focuses the signal light to the slit 3-1-1, and then collimates it through the collimator 3-1-3, and then diffracts and splits the light of different wavelengths through the spectrometer 3-1-4, and then focuses the signal light of different wavelengths to the Y direction of the planar array detector 3-1-5 through the fourth focusing lens 3-1-4. The Y direction of the planar array detector 3-1-5 corresponds to signals of different wavelengths, and the X direction corresponds to the spatial dimension information in the direction of the slit length. That is, each column of the planar array detector 3-1-5 corresponds to the spectral information of a point in the direction of the slit length. The detector signal is accumulated and integrated along the X direction (along the X direction, that is, corresponding to the slit length direction, the signal is accumulated to achieve signal integration enhancement), so that the scattered or fluorescent signal generated by the laser line excitation can be detected by line integration, thereby improving the signal intensity and detection sensitivity. Each point can also be detected individually to achieve line imaging and counting detection of signals on the excitation line, such as detection of microplastics in solutions, particulate matter in gases, and abnormal cells in blood.

[0042] Embodiment three, as Figure 3 As shown, in addition to the above-mentioned spectrum detection unit, the spectrum detection unit of the present invention can also adopt a linear array detector to realize signal detection of a specific wavelength of the spectrum signal generated by the line excitation after passing through the filter.

[0043] In summary, the present application adopts a gain resonance method in a resonant cavity to multiply the energy of the excitation light by an order of magnitude; and utilizes the line transmission characteristics of the laser and the weak absorption and scattering characteristics of the laser by gases and liquids, utilizes the slit imaging characteristics of the imaging spectrometer, and adopts a line excitation and line collection method to greatly improve the excitation and signal detection capabilities of the sample. The present application can be applied to non-transparent samples such as solids and powder samples, as well as transparent substances such as gases and liquids. It is easy to implement, and compared with the existing technology, it has a lower cost, has intracavity gain, requires a smaller amount of sample, and has a relatively high signal collection efficiency.

[0044] The above are only preferred embodiments of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A laser induced Raman and fluorescence spectroscopy testing system, characterized in that: include: Laser module, harmonic separation mirror, frequency doubling crystal, first cavity mirror, sample cell, second cavity mirror and spectrum detection unit; The laser output from the laser module passes through the harmonic separation mirror, the frequency doubling crystal and the first cavity mirror in sequence; The side of the harmonic separation mirror close to the laser module is coated with a high-transmittance film, and the side of the harmonic separation mirror close to the frequency doubling crystal is coated with a high-reflection film. The harmonic separation mirror separates the laser from the frequency doubling crystal and reflects the laser of the required wavelength to the sample pool; The first cavity mirror is used to reflect the laser from the frequency doubling crystal back to the frequency doubling crystal; The second cavity mirror is used to reflect the laser from the sample cell back to the sample cell; The spectrum detection unit is used to analyze and detect the samples in the sample pool.

2. A laser induced Raman and fluorescence spectroscopy testing system according to claim 1, characterized in that: The laser module comprises a pump laser, a wave plate and a first focusing lens. The laser outputted by the pump laser passes through the wave plate, the first focusing lens and the harmonic wave separation mirror in sequence.

3. A laser induced Raman and fluorescence spectrum testing system according to claim 2, characterized in that: A Faraday optical isolator is arranged between the pump laser and the wave plate.

4. The laser induced Raman and fluorescence spectrum testing system according to claim 2, characterized in that: The wave plate is a half wave plate.

5. The laser induced Raman and fluorescence spectrum testing system according to claim 1, characterized in that: A second focusing lens is arranged between the harmonic separation mirror and the sample cell.

6. The laser induced Raman and fluorescence spectrum testing system according to claim 1, characterized in that: It also includes a collecting reflector for collecting and reflecting the scattered or fluorescent signals generated by the sample, a collimating lens and a laser filter for collimating the scattered and fluorescent signals from the sample pool. The collimated laser passes through the laser filter and enters the spectral detection unit.

7. The laser induced Raman and fluorescence spectrum testing system according to claim 6, characterized in that: The system also includes a third focusing lens, which is arranged between the laser filter and the spectrum detection unit.

8. A laser induced Raman and fluorescence spectrum testing system according to any one of claims 1 to 7, characterized in that: The spectrum detection unit comprises a slit, a collimator, a spectrometer and a planar array detector, and the laser from the sample passes through the slit, the collimator, the spectrometer and the planar array detector in sequence.

9. The laser induced Raman and fluorescence spectrum testing system according to claim 8, characterized in that: The spectrum detection unit further includes a fourth focusing lens, which is arranged between the beam splitter and the area array detector.

10. A laser induced Raman and fluorescence spectrum testing system according to any one of claims 1 to 7, characterized in that: The spectrum detection unit includes a linear array detector.

Images