CN110632058A - Small light splitting device for Raman spectrum analysis - Google Patents
Small light splitting device for Raman spectrum analysis Download PDFInfo
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Abstract
The invention relates to a small-sized light splitting device for Raman spectrum analysis, which transmits incident light to an incident slit, wherein a filter is arranged behind the incident slit, the incident light penetrates through the incident slit and the filter to irradiate an off-axis parabolic mirror (collimating mirror), the incident light is guided to a diffraction grating, and the light dispersed by the diffraction grating is irradiated to a concave reflecting mirror in a state close to a Littrow state, so that the dispersed spectrum is focused on a detector with a cylindrical mirror, and the position of the detector and the position of the incident slit are preferably positioned on the same side of the diffraction grating, so that the light path structure is compact and the device is miniaturized. The light splitting device provided by the invention has the advantages of large relative aperture, high transfer efficiency, high spectral resolution, compact structure and small volume.
Description
Technical Field
The invention relates to a small-sized light splitting device applied to Raman spectrum analysis, in particular to a small-sized light splitting device which is more easily portable and handheld than most of prior designs and applied to a Raman spectrum instrument.
Background
The Raman spectrum is an analysis technology with no damage and high detection speed, and the basic principle is as follows: when a laser beam with a certain frequency is irradiated on a sample, molecules can scatter incident light, most scattered light (called Rayleigh scattering) has the same frequency as the incident laser beam, and only a few of the scattered light changes the propagation direction of the light, and the frequency of the scattered light is also changed and is different from that of the incident laser beam, and is called Raman scattering. The frequency shift between raman scattering and the incident laser light is called raman shift, and is related only to the molecular structure where the scattering occurs. Thanks to the rapid development of laser technology and CCD technology in recent years, the performance of the laser is increasingly improved, so that the laser intensity is stable, and the spectral bandwidth is extremely narrow; the improvement of the CCD technology enables the dark noise of the CCD detector to be lower and lower, enhances the detection capability of weak light signals and drives the Raman spectrometer to be developed rapidly. Raman spectroscopy instruments are widely used in the fields of liquid security inspection, explosives detection, drug/medicine detection, jewelry detection, biology/medicine, and the like. However, the intensity of raman scattering is very weak, which is one thousandth of the intensity of rayleigh scattering, and a large-caliber photoelectric element is needed to improve the utilization rate of light energy, so that the raman spectrometer has a complex structure, a large volume, is inconvenient to carry and is expensive. With the increasing importance of the country and the masses on food, environment and safety, the portable and handheld raman spectroscopy instruments have the advantages of nondestructive detection, high detection speed, capability of realizing on-site real-time detection and the like, so that the applications of the instruments are more and more extensive, and the instruments are a main trend in the field in terms of technical development and requirements.
Due to the low Raman signal, the signal-to-noise ratio of the Raman spectrometer is lower, long integration time measurement is needed to obtain a useful signal, and meanwhile higher requirements are provided for the stability of a laser and the heat dissipation performance of a detector. In order to shorten the measurement integration time and improve the signal-to-noise ratio of the raman spectrometer, under the condition that the grating diffraction efficiency and the detector performance are fixed, the luminous flux of the raman system is improved by increasing the numerical aperture of incident light and the light-passing area of an incident slit, but the spectral resolution of the raman system is reduced by increasing the light-passing area of the incident slit, so that for the raman system, an optical system is required to meet the requirement of large incident luminous flux and ensure high spectral resolution.
FIG. 1 shows a Czerny-Turner structure optical splitting system, referred to as C-T structure: the light rays pass through the slit 11 and irradiate the collimating concave reflecting mirror 12, the collimated light rays irradiate the plane grating 13, the spectrum lines irradiate the converging first concave reflecting mirror 14 after the grating is subjected to dispersion, and the converged spectrum is finally focused on the first detector 15. The C-T structure is commonly applied to ultraviolet, visible light and infrared wave bands, and the volume of the design of the existing light splitting system designed based on the C-T structure is small, but the system can only adopt small relative aperture (1/F #: 1/7-1/4) and high groove number grating under the condition of meeting the requirement of high spectral resolution. Currently, manufacturers of micro spectrometers on the market, such as Ocean Opticas Inc in the United states, Avants in the Netherlands, and the like, basically adopt small relative aperture (1/F #: 1/7-1/4) to design micro spectrometers with C-T structure. The collimating concave reflector and the converging concave reflector in the C-T structure light splitting system are not suitable for adopting parabolic mirrors, coma generated by the parabolic mirrors is larger than that of spherical mirrors, so that spectral resolution is poor, and plane gratings in the C-T structure light splitting system basically adopt blazed gratings. For the customized design of high spectral resolution, high luminous flux and small volume of a system required by a customer, a C-T structure light splitting system is difficult to meet the requirement of large relative aperture, and simultaneously the number of blazed grating scribes is usually non-standardized and high, so that the system needs to be customized, the cost is high, and the production period is long. The grating manufactured by the holographic method has a short production period, but the groove shape is generally sinusoidal, so that the diffraction efficiency of the grating in a C-T structure light splitting system is low (about 30 percent), and the signal-to-noise ratio of the system and the capacity of receiving weak signals are reduced.
Fig. 2 shows a transmission grating based spectroscopy system: the light rays pass through the slit 01 and irradiate the collimating lens group 02, the light rays irradiate the transmission grating 03 after being collimated, the spectral lines irradiate the converging lens group 04 after being dispersed by the grating, the spectrum after being converged is finally focused on the detector 05, and the relative aperture 1/F # of the system is 1/1.3. The WP785Raman spectrometer produced by Watatch Photonics in the United states adopts the light splitting system based on the transmission grating, and the light splitting system based on the transmission grating is commonly applied to visible light and infrared wave bands. At present, a light splitting system based on transmission gratings has a relatively large volume under the design of high spectral resolution and high luminous flux indexes (for example, a WP785Raman spectrometer is long (165mm), wide (162mm) and high (67mm)), and a collimating lens and a converging lens need to adopt a plurality of spherical single lens sheets or a plurality of aspheric single lens sheets; in addition, for the transmissive structure, the stray light is generally large, so in order to avoid the increase of the stray light of the system due to the specular reflection generated on the lens surface by the light irradiation, it is necessary to plate an antireflection film (antireflection film) on each surface of each lens. The design of the light splitting system of the portable and handheld Raman spectrum instrument is difficult to meet the requirements of volume and cost performance of the other party.
Therefore, a spectroscopic system is needed, which satisfies the requirements of high spectral resolution (better than 8cm-1 under a slit of 25 um), large relative aperture (1/F # ≥ 1/2.5), small volume (smaller than length (85mm), width (75mm) and height (72mm)) so as to be suitable for portable and handheld raman spectroscopy instruments, and the requirements are not limited by the manufacture of diffraction gratings, and the diffraction efficiency of the diffraction gratings in the optical system is high (more than 50%).
Disclosure of Invention
The invention solves the problems: the small-sized light splitting device for Raman spectrum analysis is small in size, can achieve high resolution (the spectral resolution (VIS-NIR) is superior to 8cm & lt-1 & gt by combining with the existing Bingsong detector product) and meet the requirement of large relative aperture (1/F # & gt 1/2.5), and the grating has high diffraction efficiency (the full-waveband absolute diffraction efficiency is larger than or equal to 50%), and is suitable for being applied to portable and handheld Raman spectroscopy instruments.
The technical scheme of the invention is as follows: a compact spectroscopic apparatus for raman spectroscopy, said common central plane being the YOZ plane of an optical system, characterized in that: the device comprises a light input device, an incident slit, a light filter, an off-axis parabolic mirror, a concave reflector, a diffraction grating, a cylindrical mirror and a detector, wherein:
the light input device receives incident light from a light source, and transmits the incident light to an optical fiber system on the incident slit or a front lens;
the incident light passing through the incident slit irradiates the off-axis parabolic mirror through the optical filter, and the optical filter is used for eliminating interference light outside the used wavelength and reducing stray light of an optical system;
the off-axis parabolic mirror is used for collimating incident light and correcting system aberration, and guiding the incident light to the diffraction grating;
the diffraction grating separates different wavelengths in the incident light into spectrums through the dispersion characteristic of the diffraction grating, the spectrums are transmitted back to the concave reflecting mirror in a state close to Littrow, the spectral lines are converged, system aberration is corrected, and finally the spectrums are focused on the detector;
the cylindrical mirror is used for focusing only light rays emitted within the height range of the entrance slit, reducing astigmatism and increasing light energy in a unit area on the detector, so that the response sensitivity of the detector is improved.
Preferably, the entrance slit, the optical filter, the cylindrical mirror and the detector are located on the same side of the diffraction grating; and the off-axis parabolic mirror and the concave mirror are positioned on the other opposite side.
Preferably, the surface of the diffraction grating is a plane, the groove shape of the groove of the diffraction grating is sinusoidal, and the absolute diffraction efficiency in the working waveband is over 50% in a state close to Littrow.
Preferably, the relative aperture 1/F # of the off-axis parabolic mirror is 1/5-1/2.0.
Preferably, the filter is a long-pass filter or a single-pass filter.
Preferably, the device is adapted for use in the following raman spectral bands: 0.54-0.69 um, 0.795-1.055 um, 1.093-1.445 um.
Preferably, the optical system comprises an off-axis parabolic mirror operatively positioned between the entrance slit and the diffraction grating for collimating incident light onto the diffraction grating and correcting optical system aberrations in conjunction with other optical elements in the system.
Preferably, the detector is operatively positioned closer to the diffraction grating than to the off-axis parabolic mirror. In various embodiments, the entrance slit is on the same side of the diffraction grating as the detector.
Preferably, the exit direction of the 0-order light (i.e. reflected light) of the diffraction grating is offset from the detector and the concave mirror.
In various embodiments, light emitted from the light source is passed onto the diffraction grating near collimation.
In various embodiments, a cylindrical mirror is optically positioned between the detector and the concave mirror.
In various embodiments, a filter is optically positioned between the entrance slit and the off-axis parabolic mirror.
In various embodiments, the beam splitting system may have off-axis parabolic mirrors, concave mirrors for Ultraviolet (UV), visible, and near infrared (VNIR).
In other embodiments, the light source of the optical system is received through a slit and may include a light input device for focusing light onto the entrance slit.
In other embodiments, the light input device is a fiber optic system that delivers light onto the entrance slit.
In other embodiments, the light input device is a front lens that passes light onto the entrance slit.
In other embodiments the optical system has an aspheric surface on one or more of the surfaces of the optical system.
And more particularly to a design having an optical design that achieves high optical throughput, high diffraction efficiency of the grating, low stray light, small volume, and high spectral resolution of the spectroscopic system more easily than most previous designs. Can be effectively applied to portable and handheld Raman spectroscopy instruments.
Compared with the prior art, the invention has the advantages that:
(1) the invention has compact structure, small volume and high spectral resolution, and can be effectively applied to portable and handheld Raman spectroscopy instruments.
(2) The diffraction grating in the invention is a holographic grating which has low stray light, high dispersion, high diffraction efficiency and easy manufacture.
(3) The relative aperture of the optical system can be more than or equal to 1/F # -1/2.0 from 1/5.0, which is beneficial to realizing high signal-to-noise ratio of the instrument.
(4) In the invention, 0-level light (namely reflected light) of the diffraction grating deviates from the detector and the concave reflecting mirror, and the 0-level light is easy to shield, thereby effectively reducing stray light of an optical system.
(5) The optical system has good universality in design format and can be used in different spectral ranges of ultraviolet light, visible light and near infrared light.
Drawings
FIG. 1 is a typical Czerny-Turner structure based optical splitting system design according to the prior art;
FIG. 2 is a typical transmission grating based beam splitting system design according to the prior art;
FIG. 3 is a perspective view showing the structure of a compact spectroscopic system for high spectral resolution detection of Raman spectra, according to one embodiment of the present invention;
FIG. 4 is a cross-sectional view of FIG. 3 taken along the central plane (YOZ);
FIG. 5 is a block diagram showing a compact optical splitting system apparatus for blocking optical traps in the form of a diffraction grating 0 order photophysical barrier, according to one embodiment of the present invention;
FIG. 6 is a graph for operating wavelength ranges according to one embodiment of the invention: 0.54-0.69 um and has a relative aperture of 1/F1/2.2;
FIG. 7 is a diffraction efficiency curve of the diffraction grating with the working wavelength of 0.54-0.69 um provided by the embodiment of FIG. 6;
FIG. 8 is a graph for operating wavelength ranges according to one embodiment of the invention: 0.795-1.055 um and has a small-sized light-splitting system device with a relative aperture of 1/F # -1/2.2;
FIG. 9 is a diffraction efficiency curve of the diffraction grating provided by the embodiment of FIG. 8 and having a working wavelength of 0.795-1.055 um;
FIG. 10 is a graph for operating wavelength ranges according to one embodiment of the invention: 1.093-1.445 and having a small-sized light splitting system device with a relative aperture of 1/F # -1/2.2;
FIG. 11 is a diffraction efficiency curve of the diffraction grating provided by the embodiment of FIG. 10 and having an operating wavelength of 1.093-1.445 um;
FIG. 12 is a graph for operating wavelength ranges according to one embodiment of the invention: 0.795-1.055 um and has a small-sized light-splitting system device with a relative aperture of 1/F # -1/2.0;
FIG. 13 is a graph for operating wavelength ranges according to one embodiment of the invention: 0.795-1.055 um and has a small-sized light-splitting system device with a relative aperture of 1/F # -1/3.0;
FIG. 14 is a graph for operating wavelength ranges according to one embodiment of the invention: 0.795-1.055 um and has a small-sized spectroscopic device with a relative aperture of 1/F # -1/5.0.
In the figure: the holographic plane grating holographic optical system comprises a light input device 0, a slit 1, a light filter 2, an off-axis parabolic mirror 3, a holographic plane grating 4, a concave reflector 5, a cylindrical mirror 6, a detector 7, a collimating lens group 02, a converging lens group 04, the concave reflector 5, the cylindrical mirror 6, the detector 7, an incident light beam 8, an imaging light beam 9, an incident light beam 10, an optical trap 11, a collimating concave reflector 12, a plane grating 13, a first concave reflector 14 and a first detector 15.
Detailed Description
The following further describes a compact spectroscopic system suitable for compact raman spectroscopy with reference to the accompanying drawings and examples.
In the embodiments shown in fig. 3 to 14, the spectroscopic system shows a small spectroscopic apparatus for portable small raman spectroscopic analysis, the incident light passes through an entrance slit 1 and a long pass filter 2 and irradiates on an off-axis parabolic mirror 3, the incident light is guided to a holographic plane grating 4, and is dispersed by a diffraction grating, and the dispersed light approaches a Littrow state (the Littrow state is also called a self-collimation state, and the Littrow state refers to a state that the spectrum returns along the original incident light path, but the near Littrow state refers to a state that the spectrum returns within a range of 12 to 40 degrees instead of completely returning along the original incident light path, and irradiates on a concave mirror 5, so that the dispersed spectrum is focused on a detector 7 with a cylindrical mirror 6, and the detector 7 is positioned on the same side of the diffraction grating 4 as the entrance slit 1, meanwhile, high spectral resolution, high luminous flux and low stray light of the system are easy to realize; in addition, the holographic diffraction grating with the sine-shaped groove in the light splitting system also has high diffraction efficiency (more than or equal to 50 percent), and the designs have obvious advantages compared with the C-T type structure design shown in the figure 1.
As shown in fig. 2, the optical splitting system based on transmission grating fig. 2 includes a collimating lens group 02 and a converging lens group 04, the aperture sizes of which are 37mm and 44mm, respectively, and a certain distance must be kept between the two lens groups to avoid interference; meanwhile, in order to realize high spectral resolution and high luminous flux, the system adopts a large relative aperture of 1/1.3, so that the volume of the light splitting system is 145mmx101mmx37mm and is relatively large. The embodiment of the invention shown in fig. 3 provides a perspective view of a structure of a small-sized spectroscopic system for raman spectroscopy analysis, the system comprises a light input device 0, an incident slit 1, a filter 2, an off-axis parabolic mirror 3, a holographic plane grating 4, a concave reflecting mirror 5, a cylindrical mirror 6 and a detector 7, wherein xyz is a rectangular spatial coordinate system, and a YOZ plane is a central plane of an optical system. The light input device 0, the incident slit 1, the long-pass filter 2, the cylindrical mirror 6 and the detector 7 are respectively arranged on the same side of the holographic plane grating 4, the light input device 0 penetrates through the slit 1 and the long-pass filter 2, irradiates the off-axis parabolic mirror 3, is transmitted to the holographic plane grating 4 through reflection, and an imaging light beam 9 with the dispersed working wavelength returns to the concave mirror 5 along with an incident light beam 8 in a YOZ plane in a state of being close to Littrow and finally converges on the detector 7 with the cylindrical mirror.
In the beam splitting system, the off-axis parabolic mirror 3 can be a replica product to reduce the production cost. The concave reflector 5 is preferably a spherical surface, alternatively an aspherical surface. The grating stripe groove type of the holographic plane grating 4 is preferably a sinusoidal equidistant linear groove holographic grating, and a blazed type can be selected. The detector 7 is of a linear array type, and the linear array type can be TCD1304CCD of Toshiba company or S11151-2048 of Hamamastu company.
As shown in fig. 4, the holographic planar grating 4 with scribe line density 1336 lines/mm undergoes first order dispersion p1 (e.g., short wavelength beam w1 and long wavelength beam w2) for a given wavelength range of the incident beam 10, where the 795nm wavelength beam w1 travels back along a path that is close to Littrow state with the incident beam 10 in the YOZ plane. In the present embodiment, the holographic plane grating 4 having a wavelength range of 795 to 1055nm and a 1336-division line per millimeter can be used. The beam propagation of the first-stage dispersion p1 can be optimized by using commercial optical design software ZEMAX, namely, in order to improve the beam energy of the first-stage dispersion p1 to the maximum extent and reduce the influence of stray light of the system, the beam propagation is finished under the state close to Littrow, wherein the stray light of the system not only depends on the surface quality of each optical element and the quality of electronic components, but also depends on the structure of an optical system. When the grating incidence angle a, the used wavelength lambda and the grating ruling number f satisfy the correlation formula (1) when the spectroscopic system uses the grating first-order diffraction order:
|1-λf|＜sin(a)＜2λf-1 (1)
at this time, only the first order diffraction order and the zero order light, and no other diffraction order exists, which is greatly advantageous for reducing stray light of the optical system. Meanwhile, the proper groove depth is selected, the spectrum of the first-order dispersion has higher diffraction efficiency, and particularly when the lambda f is less than 0.8 < 1.1, the average diffraction efficiency of the two polarizations can reach more than 70%, and the diffraction efficiency is higher than that of a mechanically etched grating (about 60%).
As shown in fig. 5, stray light can be eliminated by arranging an optical trap 11, incident light in the system is collimated by the off-axis parabolic mirror 3 and then irradiates on the holographic plane grating 4, and a zeroth order dispersion spectrum and a first order dispersion spectrum exist through grating diffraction, which is known to those skilled in the art. While the zeroth order dispersion spectrum is not needed by the system and can become stray light if not blocked. While serrated light traps minimize light scattering. A plurality of serrated optical traps 8 (shown in bold lines) may be provided in the light propagation path perimeter in fig. 5 to eliminate the 0 th order dispersion spectrum and other stray light.
As shown in fig. 6, an embodiment of a compact Raman532 spectroscopic system with a relative aperture of 1/F # 1/2.2 is shown that can be used for Raman spectroscopy, the system operating wavelength is in the visible range of 540nm to 690nm, the F # of the system is 2.2, the slit 1 is a rectangle with a height of 1mm and a width of 25um, and the detector 7 is a TCD1304CCD (pixel size 8umx200um) from Toshiba corporation. The slit 1, the long-pass filter 2, the cylindrical mirror 6 and the detector 7 are all positioned at the same side below the holographic plane grating 4, so that the optical system structure is more compact, and the length, width and height of the optical path volume are 78x84x15 mm. The relevant parameters of the optical system are shown in the following table 1 and table 2.
As shown in fig. 7, the absolute diffraction efficiency diagram of the holographic plane grating of the light splitting system of the embodiment of fig. 6 is shown, the number of the holographic plane grating lines is 2072 lines/mm, the grating groove shape is sinusoidal, the grating incident angle is-54.46, and the diffraction order is-1. From the figure, the absolute diffraction efficiency of the grating is above 52% in the range of the working wavelength of 540nm to 690nm, and the signal-to-noise ratio of the small Raman532 Raman spectrometer is favorably improved.
As shown in fig. 8, an embodiment of a compact Raman785 spectroscopic system with a relative aperture of 1/F # 1/2.2 for Raman spectroscopy is shown, the system operating wavelength is in the range of 795nm to 1055nm, the system F # 2.2, the slit 1 is a rectangle with a height of 1mm and a width of 25um, and the detector 7 is a S11151-2048CCD (pixel size 14umx200um) from hamastu. The slit 1, the long-pass filter 2, the cylindrical mirror 6 and the detector 7 are all positioned at the same side below the holographic plane grating 4, so that the optical system structure is more compact, and the length, width and height of the optical path volume are 71x80x15 mm. Where the spectral length of the spectroscopic system is 28mm, the spectral resolution is 0.54nm (6.3cm-1), and the wavelength units characteristic of raman spectroscopy are in brackets, in addition to nanometers, this representation is the wavenumber.
As shown in fig. 9, the absolute diffraction efficiency chart of the holographic plane grating of the light splitting system of the embodiment of fig. 8 is shown, the number of the holographic plane grating is 1321 lines/mm, the grating groove is sinusoidal, the grating incident angle is-53.32 °, and the diffraction order is-1. From the figure, the absolute diffraction efficiency of the grating is over 53 percent in the range of the working wavelength of 795nm to 1055nm, and the signal-to-noise ratio of the small Raman785 Raman spectrometer is favorably improved.
As shown in fig. 10, an embodiment of a small Raman1064 spectroscopic system with a relative aperture of 1/F # 1/2.2 for Raman spectroscopy is shown, the system operating wavelength is in the range of 1093nm to 1445nm, the F # of the system is 2.2, the slit 1 is a rectangle with a height of 1mm and a width of 25um, and the detector 7 is a S11151-2048CCD (pixel size 14umx200um) from hamastu. The slit 1, the long-pass filter 2, the cylindrical mirror 6 and the detector 7 are all positioned at the same side below the holographic plane grating 4, so that the optical system structure is more compact, and the length, width and height of the optical path volume are 73x81x15 mm. The spectral length of the spectroscopic system was 28mm, and the spectral resolution was 0.72nm (4.52 cm-1).
As shown in fig. 11, the absolute diffraction efficiency chart of the holographic plane grating of the light splitting system of the embodiment of fig. 10 is shown, the number of the holographic plane grating is 977 lines/mm, the grating groove is sinusoidal, the grating incident angle is-53.75 °, and the diffraction order is-1. From the graph, the absolute diffraction efficiency of the grating is over 54 percent in the range from the working wavelength 1093nm to 1445nm, and the signal-to-noise ratio of the small Raman1064 Raman spectrometer is favorably improved.
As shown in fig. 12, an embodiment of a compact Raman785 spectroscopic system with a relative aperture of 1/F # 1/2.0 for Raman spectroscopy is shown, the system operating wavelength is in the range of 795nm to 1055nm, the F # of the system is 2.0, the slit 1 is a rectangle with a height of 1mm and a width of 25um, and the detector 7 is a S11151-2048CCD (pixel size 14umx200um) from hamastu. The slit 1, the long-pass filter 2, the cylindrical mirror 6 and the detector 7 are all positioned at the same side below the holographic plane grating 4, so that the optical system structure is more compact, and the length, width and height of the optical path volume are 73x86x20 mm. The spectral length of the spectroscopic system was 28mm, and the spectral resolution was 0.56nm (6.64 cm-1).
As shown in fig. 13, an embodiment of a compact Raman785 spectroscopic system with a relative aperture of 1/F # 1/3.0 for Raman spectroscopy is shown, the system operating wavelength is in the range of 795nm to 1055nm, the F # of the system is 3.0, the slit 1 is a rectangle with a height of 1mm and a width of 25um, and the detector 7 is a S11151-2048CCD (pixel size 14umx200um) from hamastu. The slit 1, the single-pass filter 2, the cylindrical mirror 6 and the detector 7 are all positioned at the same side below the holographic plane grating 4, so that the optical system is more compact in structure, and the length, width and height of the optical path are 70x69x12 mm. The spectral length of the spectroscopic system was 28mm, and the spectral resolution was 0.46nm (5.47 cm-1).
As shown in fig. 14, an embodiment of a compact Raman785 spectroscopic system with a relative aperture of 1/F # 1/5.0 for Raman spectroscopy is shown, the system operating wavelength is in the range of 795nm to 1055nm, the F # of the system is 5.0, the slit 1 is a rectangle with a height of 1mm and a width of 25um, and the detector 7 is a S11151-2048CCD (pixel size 14umx200um) from hamastu. The slit 1, the long-pass filter 2, the cylindrical mirror 6 and the detector 7 are all positioned at the same side below the holographic plane grating 4, so that the optical system is more compact in structure, and the length, width and height of the optical path volume are 50x57x8 mm. The spectral length of the spectroscopic system was 28mm, and the spectral resolution was 0.38nm (4.6 cm-1).
Optical specifications and other optical parameters for embodiments of the Raman532 spectroscopy system (such as fig. 6) are provided in tables 1 and 2 below, and an illustration of typical systems known to those skilled in the art is provided.
TABLE 1 exemplary optical Specifications
TABLE 2 other optical parameters of the Raman 532F 2.2 example
| F/# | 2.2 |
| Range of wavelengths | 540nm to 690nm |
| Length of slit | 1mm |
| Width of slit | 25um |
| Type of detector | Toshiba_TCD1304mm |
| Size of picture element | 8x200um |
| Spectral length | 28mm |
| Line dispersion | 5.36nm/mm |
| Maximum full width at half maximum (FWHM) | 58.4um |
| Spectral resolution | 0.29nm(7.7cm-1) |
In each embodiment, the improved optical design is that the slit, the long-pass filter, the cylindrical mirror and the detector are all positioned at the same side below the holographic plane grating, so that the optical path structure is more compact, the occupied space is obviously small, and the improved optical design is suitable for portable and handheld Raman spectroscopy instruments. The absolute diffraction efficiency of the sinusoidal groove-shaped holographic plane grating of each embodiment is over 50%, and the signal-to-noise ratio of a Raman spectrum instrument is facilitated.
The above examples are provided only for the purpose of describing the present invention, and are not intended to limit the scope of the present invention. The scope of the invention is defined by the appended claims. Various equivalent substitutions and modifications can be made without departing from the spirit and principles of the invention, and are intended to be within the scope of the invention.
Claims (10)
1. A compact spectroscopic apparatus for Raman spectroscopy having an optical system with a common central plane, which is a YOZ plane of the optical system, characterized in that: the device comprises a light input device, an incident slit, a light filter, an off-axis parabolic mirror, a concave reflector, a diffraction grating, a cylindrical mirror and a detector, wherein:
the light input device receives incident light from a light source, and transmits the incident light to an optical fiber system on the incident slit or a front lens;
the incident light passing through the incident slit irradiates the off-axis parabolic mirror through the optical filter, and the optical filter is used for eliminating interference light outside the used wavelength and reducing stray light of an optical system;
the off-axis parabolic mirror is used for collimating incident light and correcting system aberration, and guiding the incident light to the diffraction grating;
the diffraction grating separates different wavelengths in the incident light into spectrums through the dispersion characteristic of the diffraction grating, the spectrums are transmitted back to the concave reflecting mirror in a state close to Littrow, the spectral lines are converged, system aberration is corrected, and finally the spectrums are focused on the detector;
the cylindrical mirror is used for focusing only light rays emitted within the height range of the entrance slit, reducing astigmatism and increasing light energy in a unit area on the detector, so that the response sensitivity of the detector is improved.
2. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: the incident slit, the optical filter, the cylindrical mirror and the detector are positioned on the same side of the diffraction grating; and the off-axis parabolic mirror and the concave mirror are positioned on the other opposite side.
3. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: the surface of the diffraction grating is a plane, the groove shape of the groove of the diffraction grating is sinusoidal, and the absolute diffraction efficiency in the working waveband is over 50% under the state close to Littrow.
4. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: the relative aperture 1/F # of the off-axis parabolic mirror is 1/5-1/2.0.
5. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: the optical filter is a long-pass optical filter or a single-pass optical filter.
6. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: the device is suitable for the following Raman spectrum wave bands: 0.54-0.69 um, 0.795-1.055 um, 1.093-1.445 um.
7. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: the incident light passes through the incident slit and the optical filter to irradiate the off-axis parabolic mirror, the incident light is guided to the diffraction grating, the dispersed light is dispersed by the diffraction grating, returns in a state close to a Littrow state and irradiates the concave mirror, and the dispersed spectrum is focused on the detector with the cylindrical mirror.
8. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: the detector is operatively positioned closer to the diffraction grating than to the off-axis parabolic mirror.
9. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: the 0-order light of the diffraction grating, namely the emergent direction of the reflected light deviates from the detector and the concave reflecting mirror.
10. The compact spectroscopic apparatus for raman spectroscopic analysis according to claim 1 wherein: light emitted from the light source is passed onto the diffraction grating near collimation; a cylindrical mirror is optically positioned between the detector and the concave mirror.
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