CN203965040U - Imaging spectrometer beam splitting system based on single free form surface - Google Patents

Abstract

This patent discloses a kind of imaging spectrometer beam splitting system based on single free form surface, and system is by entrance slit, free-form surface mirror, plane blazed grating and image planes composition.The feature of this patent is that the free-form surface mirror of a non-rotating symmetry of twice use serves as respectively collimating mirror and imaging lens, be equipped with the plane blazed grating of high-performance and processing technology maturation, implementation structure is simple, compact, little aberration, low distortion, high efficiency spectrometer beam splitting system.The embodiment of the imaging spectrometer beam splitting system of this patent based on single free form surface has realized good light spectrum image-forming at the visible near-infrared spectral coverage of 400-1000nm, under simple, the compact prerequisite of guarantee system, spherical aberration, coma, astigmatism, spectrum distortion and Spectral line bend etc. are proofreaied and correct preferably.This patent can be applied to the high light spectrum image-forming field of space flight, aviation.

Description

Imaging spectrometer beam splitting system based on single free form surface

Technical field

This patent belongs to imaging spectrometer design field, be specifically related to a kind of optical design of the novel imaging spectrometer beam splitting system based on single free form surface and plane blazed grating, the embodiment spectral coverage of this patent is visible near-infrared, and it is also applicable to the design of the spectrum imaging system spectrum groupware of other spectral coverages such as short-wave infrared and thermal infrared.

Background technology

Imaging spectrometer is the combination of imaging technique and spectral technique, it can obtain two-dimensional space information and the one dimension spectral information of target simultaneously, form data cube, be widely used in the numerous areas such as social production, military activity, universe and astrosurveillance and Aero-Space remote sensing.Its optical system is generally made up of preposition telescopic system and spectrum beam splitting system, and beam splitting system is determining the key property of imaging spectrometer, the key of innovation routine spectra instrument, because beam splitting system directly affects performance, the complexity of structure, the weight and volume of whole imaging spectrometer.In numerous light splitting modes, optical grating diffraction light splitting is because its structure is high without dynamic component, technology maturation, performance, good linearity, have wide spectral range and high resolution and become the light splitting means of existing imaging spectrometer main flow.The principal mode of the grating splitting system of widespread use has in the world: adopt the Czerny-Turner structure of the Offner structure of convex grating, the Dyson structure that adopts concave grating, employing plane grating etc., also have some to adopt the beam-splitting structure of gratings and prism combination.

Offner structure is total-reflection type, not limited by wave band, and its spectrum groupware is convex grating, simple and compact for structure; Dyson structure adopts transmission-type, can realize larger relative aperture and little volume, and its spectrum groupware is concave grating.Opposite planar grating, these two kinds of grating development are used more late, and the technology such as its processing, detection are relatively immature, manufacture is difficult, cost is high, design limitations is large.

Plane grating is lower as a kind of processing technology thereof maturation, cost, obtain the spectrum groupware that channel is relatively unimpeded, is the most general spectrum groupware of application now.But for convex grating and concave grating, adopt the Czerny-Turner structure of plane grating light splitting to be subject to the restriction of aberration correction, be difficult to realize large relative aperture, and along with elongated the caused chromatic variation of distortion of slit and Spectral line bend also increase acutely, there is the problem that aberration correcting capability is poor, resolution is lower.In order to make up these defects and to proofread and correct various aberrations, Czerny-Turner structure based on plane grating is through being usually used in the spectrum imaging system of the poor large F number of statuette, and in order to increase the degree of freedom of balance aberration, often all there is rotation and bias in various degree in each element, to having relatively high expectations of designing, debug, the lead time is longer.

In addition, other spectrometer beam splitting system based on plane grating generally increases the degree of freedom of balanced system by increasing the mode of component, system is comparatively complicated, need to introduce multiple lens or prism, the small skew of each prism or lens and the eccentric picture quality of system of can giving are brought serious impact, what must cause whole system debugs and tests difficulty, and the lead time is long and development cost is high.This UV light will just can reach detector through repeatedly reflecting and reflecting, and reflects at every turn and reflects and all bring light loss of energy, will inevitably cause the system efficiency of light energy utilization low.

For above problem, patent 201410120502.8 has proposed a kind of spectrometer beam splitting system based on free form surface, utilize respectively a free form surface to serve as collimating mirror and imaging lens, realize the design of the plane grating spectrograph beam splitting system based on two free form surfaces.

Summary of the invention

Combine the above, the fundamental purpose of this patent is on the basis of patent 201410120502.8, replace original two free-form surface mirrors with the form of utilizing same free-form surface mirror to serve as respectively collimating mirror and imaging lens twice, do not affecting under the prerequisite of system performance, the number of elements of minimizing system, the structure of simplification system, the cost of reduction system.This system number of elements still less, structure is simpler, compact, debug the easier while and can realize little aberration, low distortion and high-level efficiency.

The system of this patent is total-reflection type, only utilizes reaching and avoid the object of blocking from axle of visual field, does not have relative angle rotation between each optical element.System utilizes a free-form surface mirror to replace the collimating mirror and the imaging lens that in conventional planar grating splitting system, are made up of multiple lens, by twice use free-form surface mirror, realize respectively collimation and imaging, and based on the large degree of freedom of freeform optics element and non-rotating symmetry, can proofread and correct well the advantages such as multiple off-axis aberration and non-rotating symmetrical aberration, to reach the design that improves spectrometer beam splitting system image quality, simplifies system, the resetting difficulty of reduction system, reduces the volume of spectral instrument, the object of deadweight.

As shown in Figure 1, it comprises entrance slit 1, free-form surface mirror 2, plane blazed grating 3 and image planes 4 to the beam splitting system structure of this patent.Entrance slit 1 is positioned on front telescopical focal plane, is the picture of front telescope infinite distance target; Free-form surface mirror 2 twice use, serve as respectively collimating mirror and imaging lens; Grating 3 is plane blazed gratings, is the aperture diaphragm of system, and the two is coaxial for free-form surface mirror 2 and plane blazed grating 3, and does not have any relative angle rotation.The light sending from entrance slit 1 reflexes to plane blazed grating 3 through free-form surface mirror 2, light after the 3 diffraction light splitting of plane blazed grating is reflexed to free-form surface mirror 2 again, last by free-form surface mirror 2 catoptric imagings to laying in the image planes 4 of detector.

The free form surface that free-form surface mirror 2 is non-rotating symmetry, its expression formula is shown in formula (1), wherein: the curvature of putting centered by c, k is quadratic coefficients, C ₁-C ₂₇for every coefficient, (x, y, z) is the coordinate of each point on free form surface.

$\begin{array}{c}z(x,y)=\frac{c(y^2+y^2)}{1+\sqrt{1-(1+k)\left((x^2+y^2)c^2\right)}}+\\ C_{1}x+C_{2}y+\\ C_3{x}^2+C_4\mathrm{xy}+C_5{y}^2+\\ C_6{x}^3+C_7{x}^{2}y+C_{8}x{y}^2+C_9{y}^3+\\ C_{10}{x}^4+C_{11}{x}^{4}y+C_{12}{x}^2{y}^2+C_{13}x{y}^3+C_{14}{y}^4+\\ C_{15}{x}^5+C_{16}{x}^{4}y+C_{17}{x}^3{y}^2+C_{18}{x}^2{y}^3+C_{19}x{y}^4+C_{20}{y}^5+\\ C_{21}{x}^6+C_{22}{x}^{5}y+C_{23}{x}^4{y}^2+C_{24}{x}^3{y}^3+C_{25}{x}^2{y}^4+C_{26}x{y}^5+C_{27}{y}^6\end{array}---\left(1\right)$

Taking visible near-infrared spectral coverage, (0.4 μ m-1 μ beam splitting system m), as design example, has been set forth feasibility and the practicality of this patent.The parameter index of design example is as shown in table 1, and under the prerequisite of the system of guarantee simplicity, indices all reaches the suitable level of beam splitting system of utilizing convex surface or concave grating.Every coefficient of free-form surface mirror 2 is as shown in table 2, it is worth mentioning that, under existing single point diamond machining technical merit, the free form surface of mentioning in this patent using copper or aluminum metal under the prerequisite of material, its machining precision can reach 1/4 λ@632.8nm, the TOLERANCE ANALYSIS of native system shows, this machining precision can meet the tolerance of system, in the time that the method for this patent is used for short-wave infrared or thermal infrared spectral coverage, reduction that can be suitable to the requirement of Free-Form Surface Machining precision, so under existing processing conditions, can ensure the processing of the free form surface of using in this patent.

Table 1

The beneficial effect of this patent is: system operation maturation, cost are lower, function admirable and obtain beam splitter plane blazed grating that channel is unimpeded and be equipped with the free-form surface mirror of non-rotating symmetry, realize little aberration, low distortion, high efficiency beam splitting system; System element quantity is few, has reduced the optical energy loss causing due to multiple reflections or refraction, simple in structure, compact; Between each optical element in system (except image planes 4), there is not relative angle rotation, and the coaxial setting of two critical optical elements (free-form surface mirror 2, plane blazed grating 3), this has reduced the difficulty of debuging largely, has shortened widely the cycle of development; Last this patent utilizes under the prerequisite of free form surface simplied system structure, the performance that ensured system.

Table 2

C 1

C 2

C 3

C 4

C 5

C 6

C 7

0

-8.357e-6

2.1118e-3

0

2.0933e-3

0

1.698e-6

C 8

C 9

C 10

C 11

C 12

C 13

C 14

0

1.410e-6

-2.454e-9

0

-1.224e-8

0

1.914e-9

C 15

C 16

C 17

C 18

C 19

C 20

C 21

0

-3.020e-10

0

-1.484e-9

0

-3.244e-10

2.088e-12

C 22

C 23

C 24

C 25

C 26

C 27

0

8.480e-12

0

1.863e-11

0

1.324e-12

Brief description of the drawings

Fig. 1 is the structural representation of beam splitting system.

Fig. 2 is 0 visual field, and the point range figure RMS radius of ± 0.5 visual field and ± 1 visual field is with the variation of wavelength.

Fig. 3 is the variation with visual field of point range figure RMS radius under short-wavelength limit 0.4 μ m, centre wavelength 0.7 μ m and long wavelength threshold 1 μ m.

Fig. 4-6 are respectively the transfer curves under short-wavelength limit 0.4 μ m, centre wavelength 0.7 μ m and long wavelength threshold 1 μ m.

Fig. 7 is the Spectral line bend curve of system.

Fig. 8 is the spectrum distortion curve of system, and the spectrum distortion of each visual field is taking centre wavelength as reference.

Fig. 9 is the light spectrum image-forming schematic diagram of short-wavelength limit, centre wavelength and long wavelength threshold skew ± 1.6nm, is respectively from left to right 0 visual field, 0.2 visual field, 0.4 visual field, 0.6 visual field, 0.8 visual field, 1 visual field.

Embodiment

Below in conjunction with drawings and Examples, this patent is described in further detail:

As shown in Figure 1, the spectrometer beam splitting system of this patent is taking high-performance, convex grating Offner structure simple in structure and the Czerny-Turner structure based on plane grating as prototype, get its two advantage, keep away its shortcoming, realize the high-performance light splitting under and system architecture simplicity prerequisite less at component number.Beam splitting system comprises slit 1, free-form surface mirror 2, plane blazed grating 3 and image planes 4.The focal plane that slit 1 is front telephotolens, images in slit 1 from the incident beam of distant object through telescope, as the object plane of beam splitting system; Free-form surface mirror 2 twice utilization, serve as respectively collimating mirror and imaging lens, after the light beam of slit is collimated by free-form surface mirror 2, incide and on plane blazed grating 3, carry out the loose light splitting of diffraction colour, the light of different wave length after plane blazed grating 3 diffraction with different emergence angle outgoing, again pass through free-form surface mirror 2 catoptric imagings on the diverse location of image planes 4, realize light spectrum image-forming.

The design procedure of beam splitting system is:

(1), the initial configuration of system calculates, catoptron 2 and the coaxial setting of plane blazed grating, catoptron 2 twice utilization, so both can avoid re-diffraction and diffraction repeatedly, facilitated again debuging and processing of catoptron simultaneously.For aplanasia, according to Rayleigh criterion, the radius-of-curvature of catoptron 2 need meet shown in formula (2).Wherein, the diameter that D is catoptron, the radius-of-curvature that r is catoptron, the F number that F is system

$\frac{{(D/2)}^4}{8r^4}\≤\frac{\mathrm{\λ}}{4}\⇒f=r/2\≤256\mathrm{\λ}{F}^4---\left(2\right)$

Correspondingly, slit is r/2 to the distance of catoptron 2, catoptron 2 to the distance of image planes is-r/2, the simultaneously version of similar Offner, to slit 1 set one with respect to y axle from axle amount, to avoid blocking of light, at this moment can generally obtain incident angle i and the diffraction angle of grating, simultaneously according to the dispersion equation of grating, as shown in formula (3), the groove that can roughly calculate every millimeter, grating according to centre wavelength, incident angle and angle of diffraction etc. is counted 1/d.

d(sini-sinθ)＝mλ _B (3)

(2), obvious above initial configuration can not obtain good light spectrum image-forming quality, next distance between catoptron 2 radius-of-curvature, each element is set, is variable from the groove number of axle amount and grating etc., and tentatively adjust these variablees, noting controlling blocking of light (can be by arranging the form of virtual surface, control the coordinate figure of light in virtual surface), through calculating and optimization repeatedly, make the result of design approach step by step the designing technique index of system.

(3), the optimized variable of step (2) is very limited, for traditional plane grating Czerny-Turner structure, the rotation of each element has not been can optimized variable, and the design's method based on relative aperture and spectral coverage scope etc. be also better than significantly conventional Czerny-Turner structure, utilize step (2) can not overcome the picture element bringing due to plane grating, the problem such as chromatic variation of distortion and Spectral line bend, so generally can't meet the needs of use, also will be according to the width of dispersion dimension on detector, the width of space dimension, the situation of Spectral line bend and spectrum distortion and system are further optimized the parameters of system the requirement of imaging pixel quality.Arranging under the prerequisite that catoptron 2 is the described free form surface of formula (1), pitch angle of groove number, image planes and the optical axis of its front 27 coefficients and central point radius-of-curvature, quadratic coefficients, grating etc. is set to variable, system is carried out to further optimal design, make final design can meet the demand of the property indices of system.Here it is worth mentioning that, if the visual field of slit is set to along the setting of x direction of principal axis, about yoz plane symmetry, free-form surface mirror also should have symmetry about yoz plane so, so when two free form surfaces are optimized to design, the index of its x is that the coefficient of the item of odd should be set to 0, and the coefficient of the index of only optimizing x is even item can improve the efficiency of software ray tracing so widely.

Finally, according to above design procedure, this patent is with the embodiment that is designed to of visible near-infrared beam splitting system, provide design example according to the design parameter index of table 1, feasibility and the practicality of this patent are set forth, every coefficient of the free-form surface mirror 2 of using in beam splitting system is as shown in table 2, and each component parameters of system arranges as shown in table 3.Ensureing under the prerequisite of system simplicity, indices all reaches domestic other quite levels of the spectrometer of complex configuration more, and Spectral line bend is controlled in 1/8 pixel, and spectrum distortion is controlled in 1/2 pixel.

Table 4

Type	Radius/mm	Spacing/mm	Quadratic coefficients	Other
					Slit 1	Plane	93.637	0
Coordinate interrupts		0	—	The eccentric 18.26mm of Y-axis
					Free form surface 2	-104.287	-98.02	-1
Grating 3	Plane	98.02	0	100 lines are right/mm
					Free form surface 2	-104.287	-98.02	-1
Coordinate interrupts		6.71	—	-15.61 ° of X-axis rotations
					Image planes 4	Plane	—	0

Claims (2)

1. the imaging spectrometer beam splitting system based on single free form surface, it comprises entrance slit (1), free-form surface mirror (2), plane blazed grating (3) and image planes (4), it is characterized in that: from the light of entrance slit (1) outgoing through free-form surface mirror (2) collimated reflected to plane blazed grating (3), after plane blazed grating (3) diffraction light splitting, again reflexed to free-form surface mirror (2), finally by free-form surface mirror (2) reflex to image planes (4) on realize light spectrum image-forming.

2. a kind of imaging spectrometer beam splitting system based on single free form surface according to claim 1, is characterized in that: the free-form surface mirror that described free-form surface mirror (2) is non-rotating symmetry.