CN116929552A - A flat grating spectrometer based on curved prism - Google Patents

Abstract

The invention belongs to the technical field of imaging spectrum, and mainly relates to a plane grating spectrometer based on a curved prism. The optical system has greatly improved spectral performance, and the high diffraction efficiency of the planar grating realizes high signal-to-noise ratio and high dynamic measurement range. The structure of the invention realizes large-scale industrialized production, and has compact structure, small volume, light weight and simple engineering realization; realizing the design of large relative aperture of the system; the assembly process is simple, and no special requirements are made on the spacing and the relative positions of the optical elements. In the long range of 0.4-1 mu m, the spectrum resolution of the spectrometer is better than 2nm, and the spectrum bending is less than 0.5 mu m.

Description

A flat grating spectrometer based on curved prism

Technical field

The invention belongs to the technical field of imaging spectroscopy and is mainly a plane grating spectrometer based on a curved prism.

Background technique

High-resolution fine imaging spectrometers usually use aspherical correction systems to correct aberrations, by folding the position of the image plane so that the slit and image plane are placed in different planes, such as the "Littrow shortwave imaging spectrometer based on free form surfaces", including the slit , Littrow optical module, plane grating and detection module. Since the grating used is a plane diffraction grating, the existing problems are:

1. Since the slit direction of the plane grating spectroscopic module is perpendicular to the meridian plane of the system, the light emitted from different object points with the same spectral line on the slit will also produce more severe spectral line bending after passing through the plane grating. Severe spectral line bending will This will cause spectral aliasing in the system, seriously affecting the imaging quality of the system.

2. Since the system completely uses a shared collimated imaging system, it cannot achieve large relative aperture design;

3. Since free-form surfaces are difficult to process, have low precision, and are expensive, the engineering achievability is low.

4. The working wavelength of Littrow shortwave imaging spectrometer is 0.9~1.7μm. For optical design, the shorter the wavelength, the smaller the focal depth of the system, and the more difficult it is to correct aberrations. However, because the focal depth calculation formula of the system is ±2λ(D /f) ² , this structure cannot further shorten the wavelength.

In summary, continuously improving the performance of planar grating spectrometers with curved edges has become a key research direction for researchers in this field.

Contents of the invention

The present invention provides a planar grating spectrometer based on a curved prism to solve the problems existing in the prior art in terms of system imaging quality, inability to achieve large relative aperture design, low engineering realizability, and inability to further shorten the wavelength.

In order to achieve the purpose of the present invention, the technical solution of the present invention is: a plane grating spectrometer based on a curved prism, including slits, a curved prism, a collimated imaging lens group, a plane grating, and an image plane position sequentially arranged along the optical axis, The curved prism is an off-axis tilted curved lens, and the collimating imaging lens group consists of a first biconvex positive lens, a biconcave negative lens, and a second biconvex positive lens arranged in sequence.

Furthermore, the above-mentioned curved prism is an off-axis tilted curved lens, which is mainly made of optical materials with refractive index nd=1.4585 and vd=67.821.

Further, the above-mentioned first biconvex positive lens is made of optical materials with nd=1.6385, vd=55.447, the biconcave negative lens is made of optical materials with nd=1.618, vd=63.393, and the second biconvex positive lens is made of nd =1.9538, vd=32.309 made of optical materials.

Furthermore, the above-mentioned planar grating is made of an optical material whose base material is nd=1.6221 and vd=56.71.

Compared with the prior art, the advantages of the present invention are:

1. The working wavelength of the spectrometer provided by the present invention is 0.4-1 μm. Based on this, the spectral performance of the optical system of the present invention has been greatly improved. At the same time, the high diffraction efficiency of the planar grating achieves a high signal-to-noise ratio of the system. High dynamic measurement range.

2. The curved prism used in the present invention is easy to process, and the processing technology is mature. Combining the curved prism with a plane grating to correct the spectral bending of the spectrum is the innovation of the present invention. This structure makes large-scale industrial production a reality and the engineering implementation is simple.

3. Since the present invention uses a curved prism, it introduces the asymmetric optical characteristics of the prism. Through the optical characteristics of the curved prism, it effectively suppresses and compensates for the spectral curvature of the entire system, and the curved prism has a certain tilt eccentricity, achieving a large relative aperture of the system. design;

4. The present invention can compensate for the spectral curvature of a large field of view optical system by changing the inclination and eccentricity of the curved prism. The present invention has a compact structure, small volume and light weight.

5. The assembly process of the present invention is simple, and there are no special requirements for the spacing and relative positions between the optical elements, as long as the assembly process is satisfied.

6. The present invention is suitable for various airborne platforms and small satellite platforms, and can be involved in various fields such as crop ecological health detection, water quality and water body composition detection, plant vegetation diseases and insect pests detection, etc.

Description of the drawings

Figure 1 is a schematic structural diagram of the present invention;

Figure 2 is a spectral bending curve diagram.

Explanation of reference signs: 1-slit, 2-curved prism, 3-collimated imaging lens group, 3-1 first biconvex positive lens, 3-2 biconcave negative lens, 3-3 second biconvex positive lens , 4-plane grating, 5-image plane position.

Detailed ways

The present invention will be described in detail below with reference to the drawings and examples.

Referring to Figure 1, a plane grating spectrometer based on a curved prism includes a slit 1, a curved prism 2, a collimating imaging lens group 3, a plane grating 4, and an image plane position 5 arranged sequentially along the optical axis. The curved prism 2 It is an off-axis tilted curved lens, and the collimating imaging lens group 3 is composed of a first biconvex positive lens 3-1, a biconcave negative lens 3-2 and a second biconvex positive lens 3-3 arranged in sequence.

The slit 1 receives the spectral information obtained by the objective lens. Different slit widths can meet different spectral resolutions, and different slit widths will affect the signal-to-noise ratio of the system. The curved prism 2 corrects the off-axis aberration of the system through its own tilt/eccentricity. At the same time, through the characteristics of the prism itself, it produces a spectral curvature opposite to the direction of the grating plane. Through compensation and correction, the residual spectral curvature of the system is close to 0. The collimating imaging lens group 3 collimates the incident light beam and simultaneously performs convergence imaging on the diffracted light from the grating 4.

The curved prism 2 is an off-axis tilted curved lens, mainly made of optical materials with refractive index nd=1.4585 and vd=67.821. The first biconvex positive lens 3-1 is made of optical material with nd=1.6385, vd=55.447, the biconcave negative lens 3-2 is made of optical material with nd=1.618, vd=63.393, and the second biconvex lens 3-2 is made of optical material with nd=1.618, vd=63.393. The positive lens 3-3 is made of optical material with nd=1.9538 and vd=32.309. The plane grating 4 is made of an optical material whose base material is nd=1.6221 and vd=56.71.

The present invention provides an imaging spectrometer optical system based on double-arm compensation. Its numerical aperture is 0.2, and its working environment temperature is -40°C to 60°C; a detector with a pixel size of 11 μm is set at the image plane position 5 , see Figure 2. After testing, in the long range of 0.4 to 1 μm, the spectral resolution of the spectrometer is better than 2 nm, and the spectral bend is <0.5 μm, meeting the international high resolution requirements.

The above are only preferred embodiments of the present invention and do not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still belong to the present invention. The scope of protection of the technical solution of the invention.

Claims (4)

1. A plane grating spectrometer based on a curved prism is characterized in that: the optical collimator comprises a slit (1), a curved prism (2), a collimating imaging lens group (3), a plane grating (4) and an image plane position (5) which are sequentially arranged along an optical axis, wherein the curved prism (2) is an off-axis inclined curved lens, and the collimating imaging lens group (3) consists of a first biconvex positive lens (3-1), a biconcave negative lens (3-2) and a second biconvex positive lens (3-3) which are sequentially arranged.

2. A planar grating spectrometer based on a curved prism as recited in claim 1, wherein: the curved prism (2) is an off-axis inclined curved lens and is mainly made of an optical material with refractive index nd=1.4585 and vd= 67.821.

3. A planar grating spectrometer based on a curved prism as claimed in claim 1 or 2, wherein: the first biconvex positive lens (3-1) is made of an optical material with nd=1.6385 and vd= 55.447, the biconcave negative lens (3-2) is made of an optical material with nd=1.618 and vd= 63.393, and the second biconvex positive lens (3-3) is made of an optical material with nd=1.9538 and vd= 32.309.

4. A curved prism-based planar grating spectrometer as recited in claim 3, wherein: the planar grating (4) is made of an optical material with a base material nd=1.6221 and vd= 56.71.