CN106290299A - A kind of polarization diversity polarization Raman probe and optical spectrum detecting method - Google Patents
A kind of polarization diversity polarization Raman probe and optical spectrum detecting method Download PDFInfo
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Abstract
The invention discloses a kind of polarization diversity polarization Raman probe and optical spectrum detecting method, this probe includes: laser instrument (1), optical path switching device (2), gathering harvester (3), coupling filtering apparatus (4), spectrogrph (5), wave plate (6)；Described laser instrument (1) is for exporting the laser beam that collimation is parallel, and described laser beam is line polarized light or elliptically polarized light；Described optical path switching device (2) is arranged on the output light path of described laser instrument (1) Output of laser light beam；Described wave plate (6) is arranged in the light path between described laser instrument (1) and described optical path switching device (2), or, described wave plate (6) is arranged in the light path between the focus of described optical path switching device (2) and described gathering harvester (3).The solution of the present invention effectively can carry out polarization diversity process, and low cost, the size no requirement (NR) to laser beam to laser beam, and damage threshold is high.
Description
Technical Field
The invention relates to the technical field of laser excitation spectrum detection, in particular to a passive polarization Raman probe and a spectrum detection method.
Background
Raman spectroscopy (Raman spectroscopy), is a scattering spectrum. The Raman spectroscopy is an analysis method for analyzing a scattering spectrum with a frequency different from that of incident light to obtain information on molecular vibration and rotation based on a Raman scattering effect found by indian scientists c.v. Raman (man), and is applied to molecular structure research. The raman spectroscopy technology is rapidly developed and widely applied in the field of non-invasive detection due to the advantages of sensitivity, rapidity, convenient operation and the like.
In polarization raman theory, when electromagnetic radiation interacts with a system, the polarization state changes, a phenomenon known as depolarization. In raman scattering, this depolarization is closely related to the symmetry of the molecule.
In laser Raman spectrum detection, the intensity of Raman light with the polarization direction parallel to the polarization direction of incident laser is recorded as I||The Raman intensity with the polarization direction perpendicular to the polarization direction of the incident laser is denoted as I⊥The ratio of the two is rho ═ I⊥/I||Referred to as the depolarization ratio. If the depolarization ratio p is less than 0.75, the vibration can be considered to be polarized, and the vibration is then fully symmetric. If the depolarization ratio ρ is equal to 0.75, the vibration can be considered as depolarized, and the vibration is then unpairedThe product is called.
Because the laser has extremely strong linear polarization degree, when the Raman spectrum detection is carried out, the intensity of a spectrum peak is related to the structure of a molecule and the polarization state of the laser, and the polarization direction angle is also a relative quantity, so that the randomness of the Raman spectrum detection is increased. Except that some specialized or scientific raman spectrometers require polarization modulation or acquisition analysis using lasers of a particular polarization state. In general, standard raman acquisition requires the elimination of polarization effects, and the elimination of polarization characteristics is achieved by inserting a "polarization scrambler" element in the optical path between the laser and the sample, and commonly used polarization scramblers include quartz wedge polarizers and liquid crystal polarizers.
The quartz wedge polarization scrambler can convert the polarized light beam into a pseudo-random polarized light beam, and the pseudo-random polarization is used for form because the light beam passing through the polarization scrambler is not unpolarized light; but its polarization state is random. After linearly polarized light of the monochromatic light source passes through the quartz wedge polarizer, the polarization state of the linearly polarized light is subjected to spatial change. The structure of a conventional deflector consists of two quartz wedges, one of which is twice as thick as the other. The two wedges are separated by a thin metal ring. The optical axis of each wedge is perpendicular to the plane of the wedge. The included angle between the optical axes of the two crystal quartz wedges is 45 degrees. Because the device uses the difference of phase delay at different spatial positions to disturb the polarization state of incident light, an incident light spot is generally required to have a certain diameter (generally equal to or more than 6mm), so the device is not suitable for the polarization disturbance of a fine light beam and has very high cost.
The principle of the liquid crystal polarization scrambler is similar to that of a quartz wedge, and the polarization state of incident light is disturbed by the difference of phase delay amounts at different spatial positions by utilizing the inconsistency of the deflection degrees of liquid crystal molecules of different pixel points. Its advantage is relatively low size requirement of light beam, but because of the light-fast ability problem of liquid crystal molecule, its laser damage threshold is lower, is not suitable for the application of high-power laser.
Disclosure of Invention
The invention provides a passive polarization Raman probe and a spectrum detection method, aiming at solving the problems that the depolarization processing method in the prior art is high in cost and is not suitable for high-power laser.
The invention provides a passive polarization Raman probe, which comprises: the device comprises a laser, a light path conversion device, a gathering and collecting device, a coupling and filtering device, a spectrometer and a wave plate;
the laser is used for outputting collimated and parallel laser beams which are linearly polarized light or elliptically polarized light;
the light path conversion device is arranged on an output light path of the laser beam output by the laser and is used for reflecting the laser beam;
the gathering and collecting device is arranged on one side of the light path conversion device in a mode of being perpendicular to the laser beams reflected by the light path conversion device and is used for gathering the beams reflected by the light path conversion device;
the coupling filter device is arranged on the other side of the light path conversion device in a mode of being perpendicular to the laser beam transmitted by the light path conversion device and is used for carrying out optical coupling on the collected light beam and then inputting the light beam to the spectrometer;
the wave plate is arranged on a light path between the laser and the light path conversion device, or the wave plate is arranged on a light path between the light path conversion device and a focus of the gathering and collecting device.
The depolarized polarization Raman probe also has the following characteristics:
when the laser beam is linearly polarized light, the phase delay amount sigma of the wave plate is (n +1/4) lambda, wherein n is an integer, lambda is laser wavelength, and the fast axis direction angle theta of the wave plate and the linear polarization direction angle of the laser beam form a positive 45-degree angle or a negative 45-degree angle;
when the laser beam is elliptically polarized, the phase retardation sigma of the wave plate and the fast axis direction angle theta meet the following conditions:
wherein,
S＝[S0,S1,S2,S3]Tis a stokes column matrix of the laser beam.
The depolarized polarization Raman probe also has the following characteristics:
the passive polarization Raman probe also comprises a purifying optical filter which is arranged between the laser and the optical path conversion device in a mode of being perpendicular to the laser beam output by the laser;
the wave plate is arranged on the light path between the laser and the light path conversion device and comprises: the wave plate is arranged between the laser and the purification optical filter in a mode of being perpendicular to the laser beam output by the laser, or the wave plate is arranged between the purification optical filter and the optical path conversion device in a mode of being perpendicular to the laser beam output by the laser.
The depolarized polarization Raman probe also has the following characteristics:
the wave plate is arranged on the light path between the light path conversion device and the focus of the gathering and collecting device and comprises: the wave plate is arranged between the light path conversion device and the gathering and collecting device in a mode of being perpendicular to the reflected laser beam of the light path conversion device; or the wave plate is arranged on the light beam converging side of the collecting and collecting device.
The depolarized polarization Raman probe also has the following characteristics:
the passive polarization Raman probe further comprises a notch filter arranged between the light path conversion device and the gathering and collecting device.
The invention also provides a spectrum detection method, which comprises the following steps:
step 1, placing a sample at a focus of the gathering and collecting device;
step 2, outputting a collimated and parallel laser beam by using a laser, wherein the laser beam is linearly polarized light or elliptically polarized light; transmitting the laser beam to the optical path conversion device through a wave plate; the laser beam is reflected to a gathering and collecting device through the light path conversion device, and the gathering and collecting device gathers the light beam reflected by the light path conversion device at a focus where a sample is placed and collects the light beam scattered back from the sample; the light path conversion device transmits the light beam transmitted back from the collection device;
or, outputting a collimated and parallel laser beam by using a laser, wherein the laser beam is linearly polarized light or elliptically polarized light; the laser beam is reflected by the light path conversion device, and is collected at a focal point where a sample is placed by the wave plate and the collection device or is reflected by the light path conversion device through the collection device and the wave plate, and the laser beam is transmitted by the light beam scattered back from the sample; the light path conversion device transmits the light beam scattered back from the sample;
and 3, optically coupling the received light beam by the coupling filter device and then inputting the light beam into the spectrometer.
The spectrum detection method also has the following characteristics:
when the laser beam is linearly polarized light, the phase delay amount sigma of the wave plate is (n +1/4) lambda, wherein n is an integer, lambda is laser wavelength, and the fast axis direction angle theta of the wave plate and the linear polarization direction angle form a positive 45-degree angle or a negative 45-degree angle;
when the laser beam is elliptically polarized, the phase retardation sigma and the fast axis direction angle theta of the wave plate need to satisfy the following conditions:
wherein,
S＝[S0,S1,S2,S3]Tis a stokes column matrix of the laser beam.
The spectrum detection method also has the following characteristics:
the transmitting the laser beam to the optical path conversion device via the wave plate includes: and transmitting the laser beam to the optical path conversion device through the wave plate and the purification filter or through the purification filter and the wave plate.
The spectrum detection method also has the following characteristics:
the method also comprises the following steps between the step 2 and the step 3: and the notch filter receives the light beam transmitted by the light path conversion device and transmits and outputs the light beam to the coupling filter device.
The scheme of the invention can effectively carry out passive treatment on the laser beam, and has the advantages of low cost, no requirement on the size of the laser beam and high damage threshold.
Drawings
FIG. 1 is a schematic diagram of the vibration directions of natural light, vertically and right-hand circularly polarized light and one of elliptically polarized light in the spatial plane;
FIG. 2 is a block diagram of a depolarized-polarization Raman probe according to the first embodiment;
FIG. 3 is a structural diagram of a depolarized-polarization Raman probe according to a second embodiment;
FIG. 4 is a structural diagram of a depolarized Raman probe according to a third embodiment;
FIG. 5 is a block diagram of a depolarized-polarization Raman probe according to an embodiment four;
FIG. 6 is a structural diagram of a depolarized Raman probe according to an embodiment;
FIG. 7 is a block diagram of a depolarized Raman probe according to a sixth embodiment;
FIG. 8 is a block diagram of a depolarized Raman probe of the seventh embodiment;
FIG. 9 is a flowchart of a spectrum detection method according to an eighth embodiment;
FIG. 10 is a flowchart of a spectrum sensing method according to the ninth embodiment.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.
Since circularly polarized light can be decomposed into a superposition of any two orthogonal equal-intensity polarized lights with phase delay of (n +1/4) λ, where λ is the laser wavelength, the magnitude of its electric vector (i.e. intensity) remains unchanged, and the polarization direction changes with time, the period of the change is the corresponding electromagnetic wave period, and the period T of the light is extremely small (about 10 λ/c)-14～10-16s) where c is the speed of light, over a raman sampling period (ms to s order), experiences greater than 1010The polarization period is long, so that the polarization of Raman sampling polarization can be eliminated, and the effect equivalent to that of natural light can be achieved. Fig. 1 is a schematic diagram of the vibration directions of natural light, vertically linear polarized light, and right-handed circularly polarized light, and one of elliptically polarized light in the spatial plane. The polarization state of light can be fully represented in a stokes matrix, S ═ S0,S1,S2,S3]TThe above four polarization statesNormalized stokes parameters are respectively [1,0,0, 0%]T、[1,-1,0,0]T、[1,0,0,1]T、[1,0.2,0.5,0.842]TAccording to the invention, the polarization modulation device is added to modulate the original incident laser beam in a specific polarization state into circularly polarized light, so that the passive polarization Raman detection effect equivalent to natural light can be obtained. The polarization modulation device in the invention typically adopts a wave plate which is used as a common optical element, has low manufacturing cost, has no requirement on the size of a laser beam and has high damage threshold.
Example one
FIG. 2 is a block diagram of a depolarized-polarization Raman probe according to the first embodiment. A depolarized-polarization raman probe comprising: the device comprises a laser 1, a light path conversion device 2, a gathering and collecting device 3, a coupling and filtering device 4, a spectrometer 5 and a wave plate 6.
The laser 1 is used for outputting a collimated and parallel laser beam which is linearly polarized light or elliptically polarized light;
the light path conversion device 2 is arranged on an output light path of the laser beam output by the laser 1 and used for reflecting the laser beam;
the gathering and collecting device 3 is arranged on one side of the light path conversion device 2 in a mode of being perpendicular to the laser beams reflected by the light path conversion device 2 and is used for gathering the beams reflected by the light path conversion device 2;
the coupling filter device 4 is arranged on the other side of the light path conversion device 2 in a manner of being perpendicular to the laser beam transmitted by the light path conversion device 2, and is used for optically coupling the collected light beam and inputting the light beam to the spectrometer 5;
the wave plate 6 is disposed on the optical path between the laser 1 and the optical path conversion device 2. Specifically, the wave plate 6 is arranged between the laser 1 and the optical path conversion device 2 in a manner perpendicular to the laser beam output by the laser 1.
When the laser beam is linearly polarized light, the phase retardation σ of the wave plate 6 is (n +1/4) λ, where n is an integer and λ is the laser wavelength, and the fast axis direction angle θ of the wave plate 6 forms an angle of positive 45 degrees or negative 45 degrees with the linear polarization direction angle of the laser beam.
When the laser beam is elliptically polarized, the phase retardation σ and the fast axis direction angle θ of the wave plate 6 need to satisfy:
wherein,
S＝[S0,S1,S2,S3]Tfor the stokes column matrix of the laser beam, there are various ways of calculating the stokes column matrix of the beam and belong to the prior art.
Example two
FIG. 3 is a block diagram of a depolarized-polarization Raman probe according to the second embodiment. The difference between the second embodiment and the first embodiment is that the passive polarization raman probe further includes a purifying filter 7 disposed between the laser 1 and the optical path conversion device 2 in a manner perpendicular to the laser beam output by the laser 1, and the purifying filter 7 can purify the laser wavelength component and filter stray light interference. The wave plate 6 is disposed between the laser 1 and the cleaning filter 7 in a manner perpendicular to the laser beam output from the laser 1, or the wave plate 6 is disposed between the cleaning filter 7 and the optical path conversion device 2 in a manner perpendicular to the laser beam output from the laser 1.
EXAMPLE III
FIG. 4 is a structural diagram of a depolarized Raman probe according to the third embodiment. The difference between the third embodiment and the second embodiment is that the passive polarization raman probe further includes a notch filter 8 disposed between the optical path conversion device 2 and the coupling filter device 4, and the notch filter 8 is used for blocking the collected rayleigh scattering scattered light and eliminating a stray light signal of an interference band.
Another configuration of the depolarized-polarization raman probe is described below. The wave plate 6 is disposed on the optical path between the laser 1 and the optical path conversion device 2 in the first, second and third embodiments, while the wave plate 6 is disposed on the optical path between the optical path conversion device 2 and the focus of the collection device 3 in the following embodiments.
Example four
FIG. 5 is a block diagram of a depolarized-polarization Raman probe according to example four. In the fifth embodiment, the wave plate 6 is disposed between the optical path conversion device 2 and the collection device 3 in a manner perpendicular to the reflected laser beam of the optical path conversion device 2.
EXAMPLE five
FIG. 6 is a structural diagram of a depolarized Raman probe according to example five. The fifth embodiment is different from the fourth embodiment in that the passive polarization raman probe further includes a purge filter 7 disposed between the laser 1 and the optical path conversion device 2 in a manner perpendicular to the laser beam output from the laser 1 and/or a notch filter 8 disposed between the optical path conversion device 2 and the coupling filter device 4.
EXAMPLE six
FIG. 7 is a block diagram of a depolarized Raman probe according to the sixth embodiment. In the sixth embodiment, the wave plate 6 is arranged on the light beam converging side of the collecting and collecting device 3.
EXAMPLE seven
FIG. 8 is a block diagram of a depolarized Raman probe according to example seven. The seventh embodiment differs from the sixth embodiment in that the passive polarization raman probe further includes a purge filter 7 disposed between the laser 1 and the optical path conversion device 2 in a manner perpendicular to the laser beam of the laser 1 and/or a notch filter 8 disposed between the optical path conversion device 2 and the coupling filter device 4.
In the above embodiment, the wave plate 6 is used to convert linearly polarized light or elliptically polarized light into right-handed or left-handed circularly polarized light. The optical path conversion means 2 is typically a dichroic edge filter for reflecting the laser light and transmitting the signal light. The collecting and collecting device 3 is typically a focusing and collecting lens, and is used for collecting the laser light to the sample, and collecting the optical signal light reflected by the sample and collimating the optical signal light into parallel light. The coupling filter means 4 is typically a coupling lens for coupling the collected signal light into the spectrometer.
Example eight
FIG. 9 shows a spectrum detection method in the eighth embodiment, which corresponds to the spectrum detection method in the first embodiment for a depolarized Raman probe, including:
step 901, placing a sample at a focus of the gathering and collecting device 3;
step 902, outputting a collimated and parallel laser beam by using a laser 1, wherein the laser beam is linearly polarized light or elliptically polarized light; transmitting the laser beam to the optical path conversion device 2 through the wave plate 6; the laser beam is reflected to the gathering and collecting device 3 through the light path conversion device 2, and the gathering and collecting device 3 gathers the light beam reflected by the light path conversion device 2 at a focus where a sample is placed and collects the light beam scattered back from the sample; the light path conversion device 2 transmits the light beam transmitted back from the collection device 3;
in step 903, the coupling filter 4 optically couples the light beam received from the light path conversion device 2 and inputs the light beam to the spectrometer 5.
When the laser beam is linearly polarized light, the phase retardation σ of the wave plate 6 is (n +1/4) λ, where n is an integer and λ is the laser wavelength, and the fast axis direction angle θ of the wave plate 6 forms an angle of positive 45 degrees or negative 45 degrees with the linear polarization direction angle of the laser beam. (ii) a
When the laser beam is elliptically polarized, the phase retardation σ and the fast axis direction angle θ of the wave plate 6 need to satisfy:
wherein,
S＝[S0,S1,S2,S3]Tis a stokes column matrix of the laser beam.
Corresponding to the depolarized polarization raman probe in the second and third embodiments, the step 2 of transmitting the laser beam to the optical path conversion device 2 via the wave plate 6 includes: the laser beam is transmitted to the optical path conversion device 2 via the wave plate 6 and the purification filter 7 or via the purification filter 7 and the wave plate 6.
Example nine
Fig. 10 is a spectrum detection method according to the ninth embodiment, which corresponds to the depolarized raman probe according to the fourth and sixth embodiments, and the spectrum detection method includes:
step 1001, placing a sample at a focus of the gathering and collecting device 3;
step 1002, outputting a collimated and parallel laser beam by using a laser 1, wherein the laser beam is linearly polarized light or elliptically polarized light; the laser beam is reflected by the light path conversion device 2, and the light beam reflected by the light path conversion device 2 is gathered at a focal point where a sample is placed by the gathering and collecting device through the wave plate 6 and the gathering and collecting device 3 or the gathering and collecting device 3 and the wave plate 6 and the light beam scattered back from the sample is transmitted by the gathering and collecting device; the light path conversion device 2 transmits the light beam scattered back from the sample;
in step 1003, the coupling filter 4 optically couples the light beam received from the light path conversion device 2 and inputs the light beam to the spectrometer 5.
Corresponding to the passive polarization raman probe comprising the notch filter 8 in the above embodiment, the method in the above method embodiment further comprises: the notch filter 8 receives the light beam transmitted by the optical path switching device 2 and transmits and outputs the light beam to the coupling filter 4.
In the method, the laser beam can be directly output in space by the laser, or output after being expanded by the laser, or output after being collimated by the fiber coupled laser.
The scheme of the invention can effectively carry out passive treatment on the laser beam, and has the advantages of low cost, no requirement on the size of the laser beam and high damage threshold.
The above-described aspects may be implemented individually or in various combinations, and such variations are within the scope of the present invention.
It is to be noted that, in this document, the terms "comprises", "comprising" or any other variation thereof are intended to cover a non-exclusive inclusion, so that an article or apparatus including a series of elements includes not only those elements but also other elements not explicitly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising … …" does not exclude the presence of additional like elements in the article or device comprising the element.
The above embodiments are merely to illustrate the technical solutions of the present invention and not to limit the present invention, and the present invention has been described in detail with reference to the preferred embodiments. It will be understood by those skilled in the art that various modifications and equivalent arrangements may be made without departing from the spirit and scope of the present invention and it should be understood that the present invention is to be covered by the appended claims.
Claims (9)
1. A passive polarized raman probe, comprising: the device comprises a laser (1), a light path conversion device (2), a gathering and collecting device (3), a coupling and filtering device (4), a spectrometer (5) and a wave plate (6);
the laser (1) is used for outputting collimated and parallel laser beams which are linearly polarized light or elliptically polarized light;
the light path conversion device (2) is arranged on an output light path of the laser beam output by the laser (1) and is used for reflecting the laser beam;
the gathering and collecting device (3) is arranged on one side of the light path conversion device (2) in a mode of being perpendicular to the laser beams reflected by the light path conversion device (2) and is used for gathering the beams reflected by the light path conversion device (2);
the coupling filter device (4) is arranged on the other side of the light path conversion device (2) in a mode of being perpendicular to the laser beam transmitted by the light path conversion device (2), and is used for optically coupling the collected light beam and inputting the light beam to the spectrometer (5);
the wave plate (6) is arranged on a light path between the laser (1) and the light path conversion device (2), or the wave plate (6) is arranged on a light path between the light path conversion device (2) and a focus of the gathering and collecting device (3).
2. The passive polarized Raman probe of claim 1,
when the laser beam is linearly polarized light, the phase delay amount sigma of the wave plate (6) is (n +1/4) lambda, wherein n is an integer, lambda is laser wavelength, and the fast axis direction angle theta of the wave plate (6) and the linear polarization direction angle of the laser beam form a positive 45-degree angle or a negative 45-degree angle;
when the laser beam is elliptically polarized, the phase delay amount sigma and the fast axis direction angle theta of the wave plate (6) satisfy the following conditions:
wherein,
S＝[S0,S1,S2,S3]Tis a stokes column matrix of the laser beam.
3. The passive polarized Raman probe of claim 1 or 2,
the passive polarization Raman probe also comprises a purifying optical filter (7) which is arranged between the laser (1) and the optical path conversion device (2) in a mode of being perpendicular to the laser beam output by the laser (1);
the wave plate (6) is arranged on a light path between the laser (1) and the light path conversion device (2) and comprises: the wave plate (6) is arranged between the laser (1) and the purifying filter (7) in a mode of being perpendicular to the laser beam output by the laser (1), or the wave plate (6) is arranged between the purifying filter (7) and the optical path conversion device (2) in a mode of being perpendicular to the laser beam output by the laser (1).
4. The passive polarized Raman probe of claim 1 or 2,
the wave plate (6) is arranged on the light path between the light path conversion device (2) and the focus of the gathering and collecting device (3) and comprises: the wave plate (6) is arranged between the light path conversion device (2) and the collection and collection device (3) in a manner of being perpendicular to the reflected laser beam of the light path conversion device (2); or the wave plate (6) is arranged on the light beam converging side of the gathering and collecting device (3).
5. The passive polarized Raman probe of claim 1,
the passive polarization Raman probe further comprises a notch filter (8) arranged between the optical path conversion device (2) and the gathering and collecting device (3).
6. A method of spectral detection, comprising:
step 1, placing a sample at a focus of the gathering and collecting device (3);
step 2, outputting a collimated and parallel laser beam by using a laser (1), wherein the laser beam is linearly polarized light or elliptically polarized light; transmitting the laser beam to the optical path conversion device (2) through a wave plate (6); the laser beam is reflected to a gathering and collecting device (3) through the light path conversion device (2), and the gathering and collecting device (3) gathers the light beam reflected by the light path conversion device (2) at a focal point where a sample is placed and collects the light beam scattered back from the sample; the light path conversion device (2) transmits the light beam transmitted back from the collection and collection device (3);
or outputting a collimated and parallel laser beam by using a laser (1), wherein the laser beam is linearly polarized light or elliptically polarized light; the laser beam is reflected by the light path conversion device (2), and the laser beam reflected by the light path conversion device (2) is gathered at a focal point where a sample is placed through the wave plate (6) and the gathering and collecting device (3) or the gathering and collecting device (3) and the wave plate (6) and transmits the beam scattered back from the sample; the light path conversion device (2) transmits the light beam scattered back from the sample;
and 3, the coupling filter device (4) optically couples the received light beams and inputs the light beams into the spectrometer (5).
7. The method for spectral detection according to claim 6, comprising:
when the laser beam is linearly polarized light, the phase delay amount sigma of the wave plate (6) is (n +1/4) lambda, wherein n is an integer, lambda is laser wavelength, and the fast axis direction angle theta of the wave plate (6) and the linear polarization direction angle form a positive 45-degree angle or a negative 45-degree angle;
when the laser beam is elliptically polarized, the phase delay amount sigma and the fast axis direction angle theta of the wave plate (6) need to satisfy the following conditions:
wherein,
S＝[S0,S1,S2,S3]Tis a stokes column matrix of the laser beam.
8. The method for spectral detection according to claim 6, comprising:
the transmitting the laser beam to the optical path conversion device (2) via the wave plate (6) comprises: the laser beam is transmitted to the optical path conversion device (2) via the wave plate (6) and the purification filter (7) or via the purification filter (7) and the wave plate (6).
9. The method for spectral detection according to claim 6, comprising:
the method also comprises the following steps between the step 2 and the step 3: the notch filter (8) receives the light beam transmitted by the light path conversion device (2) and transmits and outputs the light beam to the coupling filter device (4).
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