CN102944310B - Spectral resolution adjustable interference imaging spectrometer - Google Patents

Abstract

An interference imaging spectrometer with adjustable spectral resolution, including a front telescopic system, a polarizer, two identical Wollaston prisms, an analyzer, an imaging mirror and an area array detector sequentially arranged in the same optical path, wherein The crystal optical axes of the first Wollaston prism left wedge and the second Wollaston prism right wedge are parallel to the prism incident surface, and perpendicular to the main optical axis of the light path, the crystals of the first Wollaston prism right wedge and the second Wollaston prism left wedge The optical axis is perpendicular to the crystal optical axis and the main optical axis of the optical path of the first Wollaston prism left wedge and the second Wollaston prism right wedge. The spectral resolution capability of the interference imaging spectrometer proposed by the invention is adjustable, and the adjustment range is wide. For different detection targets, using this technology, only useful spectral data can be obtained, which can not only meet the needs of multi-target and multi-task spectral image detection, but also greatly reduce the occupation of storage space and communication bandwidth, and effectively shorten the data processing time. , improve the signal-to-noise ratio of the system, so that the overall performance of the instrument can be optimized.

Description

An Interferometric Imaging Spectrometer with Adjustable Spectral Resolution

technical field

The invention relates to an interference imaging spectrometer, in particular to an interference imaging spectrometer with adjustable spectral resolution.

Background technique

Imaging spectroscopy technology is an advanced optical detection technology developed in the 1980s that can simultaneously acquire the target image and the spectral information of each point on the image, and the acquired data is called "data cube" [Sellar R G, Boreman G D2005Opt. Eng.44013602.]. The instrument that does this is called an imaging spectrometer. According to different spectrum acquisition principles, imaging spectrometers can generally be divided into four types: dispersion type, interference type (Fourier transform type), filter type, and computed tomography type. Among them, the most widely used are dispersion type and interference type. The dispersion type uses prism or grating as the dispersion element to obtain the target spectrum, which has the advantages of mature technology and stable performance, but the structure is relatively complex, and a small incident slit is required to achieve high spatial resolution and spectral resolution, which limits the luminous flux and signal noise Compared with [Sellar R G, Boreman G D2005Appl.Opt.441614.], it is not conducive to the detection of low-light targets. The interference type uses the Fourier transform spectral characteristics of double-beam interference to achieve spectral data acquisition, and has the advantages of large luminous flux, high wavelength accuracy, and wide spectral detection range. Most of the early structures were Michelson type, and at the same spectral resolution, the luminous flux is about 190 times that of the grating type [Bell R J1972Introductory Fourier Transform Spectroscopy (New York: Academic Press).]. However, when it works, it needs precise and stable moving mirror scanning, so it cannot detect the target spectral information in real time, and the application environment and conditions are also greatly limited. To solve this problem, a static interferometric imaging spectrometer has been developed, which has become the mainstream of interferometric imaging spectrometers [Barducci A, Guzzi D, Lastri C, Marcoionni P, Nardino V, Pippi I2010Opt.Express1811622.], [Li J, Zhu JP , Wu HY2010Opt.Lett.353784.] [LiJ, ZhuJP, Hou X.2011Opt.Commun.2841127.].

Static interferometric imaging spectrometers are divided into reflection type (such as Sagnac interferometric imaging spectrometer) and birefringent type according to their optical path structure and beam splitter. The former mainly uses semi-transparent and semi-reflective beam splitters and plane mirrors to achieve double-beam interference of incident light. The latter uses a birefringent crystal beam splitter to split the incident light into two linearly polarized beams whose vibration directions are perpendicular to each other, and then passes through the analyzer to make the two beams have the same vibration direction and interfere. At present, Wollaston prism [Smith WH, Hammer PD1996Appl.Opt., 352902.], [Fox DJ, Velde HT, Preza C, O'Sullivan JA, Smith WH, Woolsey TA2006Appl.Opt.453009.] and Savart polarized light have been developed Mirror [Li J, ZhuJP, Hou X.2011Opt.Commun.2841127.] A birefringent interference imaging spectrometer with a beam splitter as the core. It has played a major role in the fields of earth resource census, disaster early warning and monitoring, environmental pollution monitoring, weather forecasting, and deep space exploration.

Unfortunately, once the above two static imaging spectrometer systems are determined, parameters such as spectral resolution and spectral range cannot be changed. In order to meet the requirements of different tasks, it is necessary to have high spectral resolution and wide spectral range［Chen B, Wang MR, Liu ZQ, Yang JJ2007Opt.Lett.321518.］, which will lead to a decrease in the signal-to-noise ratio of the instrument, and the spectral image data volume surged. The decrease of signal-to-noise ratio will affect the quality of image acquisition, and the increase of data volume will occupy more storage space and wider communication channel, and also prolong the time of data acquisition and processing. These problems are particularly prominent in aerospace remote sensing. .

Taking the Sagnac space-modulated interferometric imaging spectrometer carried by China's Chang'e-1 as an example, due to the limitation of on-board storage space and communication bandwidth, its spectral resolution is 325.25cm ^-1 , and the corresponding number of spectral channels is 32. In order to balance Due to the contradiction between the spectral resolution required by the task and the amount of data, the interference fringe data collected by the CCD can only be transmitted by half, and the energy utilization rate is therefore reduced by 50%[Xue B2006Ph.D.Dissertation(Xi'an:Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences) (in Chinese), Xue Bin 2006 doctoral dissertation (Xi'an: Xi'an Institute of Optics and Fine Mechanics, Chinese Academy of Sciences)]. It has become the main bottleneck restricting the development of imaging spectral remote sensing instruments.

In 2007, someone proposed a method to adjust the resolution of the spectrometer by rotating the Savart polarizer to adjust the transverse shear amount, but the adjustment range of this method is very narrow, and the aperture of the prism will be reduced after rotation [Jian Xiaohua, Zhang Chunmin, Sun Yao, Wu Lei. 2007 Acta Optics Sinica, 27643.], which is not conducive to practical application.

Contents of the invention

The purpose of the present invention is to provide a simple and compact structure, large luminous flux, high stability, simple process implementation, and can realize the detection of target two-dimensional image and one-dimensional spectral information. At the same time, it also has the unique advantage of adjustable spectral resolution. While meeting the needs of multitasking, it can reduce the occupation of storage space and communication data transmission bandwidth by unnecessary data, shorten data processing time, and improve the system signal-to-noise ratio, so that the overall performance of the instrument can reach the optimal spectral resolution adjustable interference Imaging spectrometer.

In order to achieve the above object, the technical solution adopted by the present invention is: comprise the front telescopic system, the polarizer, two identical and adjustable pitch first and second Wollaston prisms WP ₁ and WP that are arranged in the same optical path successively _2. Analyzer, imaging mirror and area detector, wherein the crystal optical axes of the left wedge of the first Wollaston prism WP ₁ and the right wedge of the second Wollaston prism WP ₂ are parallel to the incident surface of the prism, and are aligned with the main optical axis of the optical path Vertically, the crystal optical axis of the first Wollaston prism WP ₁ right wedge and the second Wollaston prism WP ₂ left wedge and the crystal optical axis of the first Wollaston prism WP ₁ left wedge and the second Wollaston prism WP ₂ right wedge and the main optical axis of the optical path are vertical.

Aiming at the problems of fixed spectral resolution and insufficient system performance of dispersive and static interferometric imaging spectrometers, the present invention uses two identical Wollaston prisms to laterally cut the target light source into two virtual light sources at infinity, And there is a certain amount of transverse shear between the two light sources, and then through the imaging mirror imaging, interference occurs on the focal plane, so as to obtain the target spectrum and image data, and realize the real-time, high spectral resolution (adjustable) detection of the target.

The instrument system has a coaxial optical path, simple and compact structure, no moving mirror scanning mechanism, large luminous flux, high stability, simple process realization, detection function that can obtain target two-dimensional image and one-dimensional spectral information, and also has spectral resolution The unique advantage of being adjustable and having a wide adjustment range. For different detection targets, using this technology, only useful spectral data can be obtained, which can not only meet the needs of multi-target and multi-task spectral image detection, but also greatly reduce the occupation of storage space and communication bandwidth, and effectively shorten the data processing time. , improve the signal-to-noise ratio of the system, so that the overall performance of the instrument can be optimized.

Description of drawings

Fig. 1 is a structural diagram of the present invention, and its beam splitter is composed of two identical first and second Wollaston prisms WP ₁ (31) and WP ₂ (32).

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Referring to Fig. 1, the present invention includes a pre-telescopic system 1, a polarizer 2, two identical first and second Wollaston prisms WP ₁ 31 and WP ₂ 32 with an adjustable spacing, which are sequentially arranged in the same optical path, and a detector Polarizer 4, imaging mirror 5 and area array detector 6, wherein the crystal optical axes of the first Wollaston prism WP ₁ 31 left wedge and the second Wollaston prism WP ₂ 32 right wedge are parallel to the prism incident surface, and are aligned with the main optical path The optical axis is perpendicular to the crystal optical axis of the first Wollaston prism WP ₁ 31 right wedge and the second Wollaston prism WP ₂ 32 left wedge and the crystal optical axis of the first Wollaston prism WP ₁ 31 left wedge and the second Wollaston prism WP ₂ 32 right The crystal optical axis of the wedge plate and the main optical axis of the optical path are vertical.

The spectral resolution of the spectrometer can be changed by adjusting the interval between WP ₁ 31 and WP ₂ 32 .

The work of the present invention is as follows: the light that the target emits is collected by the front telescopic system 1 and becomes parallel light after being collimated, and becomes a beam of linearly polarized light after passing through the polarizer 2, and this beam of linearly polarized light passes through the first, Two Wollaston prisms WP ₁ 31 and WP ₂ 32 are divided into two beams of linearly polarized light with a certain amount of transverse shear, parallel propagation direction, equal amplitude, and perpendicular vibration directions, and then pass through the analyzer 4, and the two beams of linearly polarized light Having the same vibration direction, they are finally converged to the focal plane by the imaging mirror 5 to form the target image and interference fringes, and are received by the area array detector 6 . The received interference image can be reconstructed and demodulated to obtain a complete two-dimensional image and one-dimensional spectral data of the target.

The difference is that British scholars Harvey and Fletcher-Holmes[Harvey AR, Fletcher-Holmes DW2004Opt.Express125368.] also proposed a staring birefringent interferometric imaging spectrometer using two Wollaston prisms. The beam splitter and the second Wollaston prism move up and down to realize the function similar to the Michelson moving mirror, which is essentially different from the present invention.

Carrying out Fourier transform to the interference fringes obtained by the present invention can obtain target spectral data, and its resolution can be expressed as (Guangzhou: Sun Yat-sen University Press)]:

$\mathrm{<span\; class="notranslate">\; \&Delta;\&sigma;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; OPD</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula, Δσ is the wave number representation of the spectral resolution, and its unit is cm ^-1 , and _OPDM is the maximum optical path difference that the interferometer can achieve. The optical path difference OPD can be expressed as

$\mathrm{<span\; class="notranslate">\; OPD</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; d</span>}\frac{\mathrm{<span\; class="notranslate">\; x</span>}}{\mathrm{<span\; class="notranslate">\; f</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula, d is the distance between WP ₁ and WP ₂ to separate the two beams of parallel light, that is, the amount of transverse shear, i is the incident angle of light, f is the focal length of the imaging mirror, x is the coordinate perpendicular to the interference fringes, and its zero point is located in the imaging mirror Center of the focal plane.

It can be seen from the above formula that the spectral resolution of the interference imaging spectrometer is determined by the transverse shear amount d of the beam splitter, the focal length f of the imaging mirror, the number of CCD pixels perpendicular to the interference fringe direction (generally called the spectral dimension) and the pixel size decided together. Once the previous interference imaging spectroscopic instrument has been processed and assembled, the shear amount of the beam splitter, the focal length of the imaging mirror and the parameters of the CCD detector cannot be changed, so it is difficult to adjust the spectral resolution. The key to the adjustable spectral resolution proposed by the present invention lies in the adjustable transverse shearing amount of the beam splitter.

The optical path difference in the crystal is deduced by ray tracing method, so that the specific expression of the spectral resolution can be obtained as

${\mathrm{<span\; class="notranslate">\; \&phi;\&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; SZBIS</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; oe</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; g</span>}{\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; oe</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; oe</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; eo</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; g</span>}{\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; eo</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; eo</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; i</span>}}$

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; f</span>}}{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; oe</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; oe</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; oe</span>}}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; eo</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; g</span>}{\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&phi;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; eo</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; eo</span>}}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, t is the thickness of a single Wollaston prism in the beam splitter, g is the distance between two Wollaston prisms, θ is the prism structure angle, i is the maximum incident angle of light, f is the focal length of the imaging mirror, and x is half of the spectral dimension of the CCD photosensitive surface length. θ _2oe and θ _2eo are the incident angles of oe light and eo light on the right interface of WP ₁ respectively, and φ _2oe and φ _2eo are their refraction angles in air.

It can be seen from the above analysis that it is feasible to adjust the spectral resolution by changing the air gap g. It must be noted here that the lower limit of the spectral resolution adjustment range is zero for the air interval g, while the upper limit is limited by the number of pixels in the CCD spectral dimension, which must satisfy the sampling theorem［Sellar R G, Rafert J B1994 Opt.Eng.333087. ]:

${\mathrm{<span\; class="notranslate">\; \&Delta;\&sigma;</span>}}_{\mathrm{<span\; class="notranslate">\; SZBIS</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In the formula, N is the number of pixels in the CCD spectral dimension, and λ _min is the minimum detection wavelength of the spectrometer. Accordingly, the structural parameters of the beam splitter can be designed according to the requirements of different target detection, so that the adjustable range of its spectral resolution can meet the needs of multiple tasks.

Compared with other birefringent interference imaging spectrometers or window-scanning interference imaging spectrometers, the interference imaging spectrometer proposed by the present invention has the advantage of adopting a new beam splitter structure and realizing the spectral resolution adjustment function. It can conveniently and effectively adjust the spectral resolution. While meeting the needs of multi-tasking, it can reduce the occupation of storage space and communication data transmission bandwidth by unnecessary data, shorten the data processing time, and improve the system signal-to-noise ratio, so that the overall performance of the instrument can reach best. Secondly, the working principle of the system determines that it does not need the moving mirror pushbroom similar to the Michelson interferometer to obtain the spectrum and image data of the target, so it has strong anti-vibration ability and good adaptability to aerospace and field environments. Third, the system has no slit and high luminous flux. Compared with the spatial modulation spectrometer, it adopts the window scanning data acquisition mode, cancels the setting of the slit, and has a 2D spatial field of view. In addition, the structure of the whole system is simple and compact, and the design, processing and modulation are convenient, which is very beneficial to the popularization and application of the new imaging spectropolarimeter.

In addition, the invention has no moving mirror scanning mechanism, coaxial optical path, simple and compact structure, large luminous flux, high stability, simple process realization, and can realize the real-time detection function of the target two-dimensional image and one-dimensional spectral information, and also has spectral resolution The unique advantage of adjustable rate, the spectral resolution of the instrument can be continuously adjusted in a wide range. A large number of practical experience and theoretical studies have shown that different observation targets and different applications have very different requirements for the spectral resolution of remote sensors. For different applications, using spectral resolution adjustment technology to obtain only useful spectral data can not only meet the task requirements, but also reduce the occupation of storage space and communication bandwidth, and shorten the data processing time, so that the overall performance of the instrument can reach the best. excellent.

Claims (1)

1. An interference imaging spectrometer with adjustable spectral resolution, characterized in that it includes a pre-telescope system (1), a polarizer (2), and two identical and adjustable distances arranged in the same optical path. The first and second Wollaston prisms WP ₁ (31) and WP ₂ (32), analyzer (4), imaging mirror (5) and area array detector (6), wherein the first Wollaston prism WP ₁ (31) The crystal optical axis of the left wedge and the second Wollaston prism WP ₂ (32) and the right wedge are parallel to the incident surface of the prism and perpendicular to the main optical axis of the optical path. The right wedge of the first Wollaston prism WP ₁ (31) and the second Wollaston The crystal optical axis of the left wedge of prism WP ₂ (32) is identical to the crystal optical axis of the first Wollaston prism WP ₁ (31) left wedge, the crystal optical axis of the second Wollaston prism WP ₂ (32) right wedge and the main optical axis of the optical path. vertical.