CN101377569A - Prism-grating-prism imaging system - Google Patents

Abstract

The invention discloses a prism-grating-prism spectrum imaging system which is integrated with the imaging technology and the light-splitting technology and has the direct vision property. The imaging system is mainly composed of a collimator objective, a prism-grating-prism (PGP) light-splitting element and an imaging objective. The prisms of the PGP light-splitting element are in an axisymmetric distribution, the light incident angle and the light diffraction angle on the grating meet the bragg conditions of grating; the collimator objective and the imaging objective are in a four glass system structure, the object space and the image space meet telecentric optical paths, and the surface of a receiver has mean illunication. The system has the advantages of higher light energy transmission, favorable imaging quality, direct vision, small volume, easy carrying, high spectral resolution and easy processing, assembly and adjustment. All the lenses or prisms are made of common domestic common glass, so the mass production cost is reduced. The imaging system can be used in the spectral cameras in the field of biomedicine, and also can be made into a civil hyper-spectral imaging system such as a pen type spectroscope and the like.

Description

Prism-grating-prism imaging system

Technical field

The present invention relates to a kind of integrated picture and light splitting technology in the spectrum imaging system of one, particularly a kind of spectrum imaging system with direct-view property.

Background technology

Imaging spectrometer combines optical imagery and these two kinds of time-honored technology of spectrum beam split, makes it to obtain simultaneously the spatial image and the abundant spectral information of object, has the advantage of collection of illustrative plates unification.Eighties of last century was subjected to various countries scientific research institution always and has paid attention to greatly since the eighties, carried out having had in the observations such as land, atmosphere, ocean on the Aeronautics and Astronautics device widely and used.

Light splitting technology mainly contains methods such as optical filter, prism, binary optical elements, interference beam split, and wherein prism or grating beam splitting are a kind of beam split modes of traditional, comparative maturity.In traditional prism or grating spectrum instrument, often have an angle of deviation problem, promptly incident beam and outgoing beam be not on same axis, the system that constitutes like this belongs to typically from axle system, exist volume big, debug defectives such as difficulty, poor stability.Adopt different prism combinations can make the light-splitting device of direct-view, such as Amici Prism, light beam directly advances directly, but the direct viewing type light-splitting device chromatic dispersion of making up with prism merely is non-even row, has limited the spectral resolution of some wave band.([J] uses laser in a literary composition of " holographic prism grating and pen type spectroscope ", 1998,18 (2): 67-69), the beam splitter of a kind of prism grating (Grism) is disclosed, though this The Application of Technology has reduced volume, but, limited the raising of capacity usage ratio because it has adopted blazed grating.

Valtion Teknillinen (VTT) lab design in 1992 spectrum groupware of prism-grating-prism (PGP) combination, can reach the advantage of direct-view property, and use body holographic phase grating, improved diffraction efficiency.Before the present invention makes, Mauri Aikio. " Hyperspectral prism-grating-prism imaging spectrograph " (VTTPublications, 2001,435:15-114) in the literary composition, disclose a kind of imaging spectrum system, it has adopted the PGP technology.In the imaging spectrum system that it provides, two prism vertex angle differences of PGP element, the diaphragm of system is placed near the grating, collimator objective and image-forming objective lens are three glass structures, therefore, total system is still compact inadequately, and length and volume are bigger, desired pixel size is 23 microns * 23 microns, and the spectrometer image quality has been subjected to certain restriction.

Summary of the invention

The objective of the invention is to overcome the deficiency that prior art exists, a kind of spectral resolution height is provided, image quality is better, compact conformation, and volume is littler, and easily the direct-view spectrum imaging system that reduces production costs is debug in processing.

For achieving the above object, the technical scheme of confession of the present invention is: a kind of prism-grating-prism imaging system is provided, it comprises beam splitter, collimator objective and the image-forming objective lens of prism-grating-prism (PGP) combination, described collimator objective is the four-piece type lens structure, wherein, from entrance slit second eyeglass backward is negative power, and its excess-three piece eyeglass is positive light coke; Described PGP beam splitter, its body holographic phase grating satisfies Bragg condition, and two prisms on a grating left side and the right distribute axisymmetricly; Described image-forming objective lens is identical with collimator objective, and the eyeglass of collimator objective and image-forming objective lens distributes axisymmetricly about the PGP beam splitter; System is 5.0～5.5 inclinations of spending as plane and optical axis, and the diaphragm of system is placed on the grating, satisfies thing, telecentric beam path in image space.

The holographic phase grating constant of described body is that every millimeter 500～600 line is right.

The object space numerical aperture of prism-grating-prism imaging system is 0.19, and linear field is 7.6mm, and magnification is 1:1; Its operation wavelength is in 420～760nm scope; Its length dimension is less than 85mm.

Compared with prior art, advantage of the present invention is: spectrum imaging system adopts the beam splitter of prism-grating-prism (PGP) combination, therefore, has direct-view, and compact conformation, and volume is littler, and the length of system only is 85mm; Two prism axis symmetries about the PGP element adopt the higher body holographic phase grating of diffraction efficiency, satisfy Bragg condition, have improved the energy transmitance of system; Diaphragm is placed on the grating, satisfies thing, telecentric beam path in image space, can reach uniform energy distribution at detector surface; Collimator objective and image-forming objective lens have adopted the symmetrical structure design, are made up of four sheet glass eyeglasses, and image quality is better; In the system the eyeglass that uses or prism all be homemade glass, can reduce production costs, be suitable for producing in batches, as be applied to the spectrum camera of biomedical sector, also can be made into the civilian ultra-optical spectrum imaging systems such as spectroscope of pen type.

Description of drawings

Fig. 1 is the structural representation of the prism-grating-prism imaging system that provides of the embodiment of the invention;

Fig. 2 is the light path synoptic diagram of the prism-grating-prism imaging system that provides of the embodiment of the invention;

Fig. 3 is the structural representation of prism grating prism (PGP) element in the prism-grating-prism imaging system that provides of the embodiment of the invention;

Fig. 4 is the ray tracing point range figure of the optical system that provides of the embodiment of the invention;

Fig. 5 is the encircled energy curve map of the optical system that provides of the embodiment of the invention;

Fig. 6 is the relative exposure curve map of the optical system that provides of the embodiment of the invention;

Fig. 7 is the transfer curve figure of the optical system that provides of the embodiment of the invention;

Wherein, 1, entrance slit; 2, collimator objective; 3, PGP beam splitter; 4, image-forming objective lens; 5, as the plane; 6, optical axis; 7, the light of three kinds of different wave lengths of outgoing after the chromatic dispersion beam split; 8～10, the chief ray of the light of three kind of different wave length; 11, a left side (first) prism; 12, substrate; 13, body holographic phase grating; 14, cover glass; 15, right (second) prism.

Embodiment

Below in conjunction with drawings and Examples technical scheme of the present invention is further elaborated:

Embodiment one:

Fig. 1 is the structural representation of the prism-grating-prism imaging system that provides of the embodiment of the invention.Referring to accompanying drawing 1,1st, entrance slit; The 2nd, collimator objective is the four-piece type structure, wherein, is negative power from entrance slit second eyeglass backward, and its excess-three piece eyeglass is positive light coke; The 3rd, prism grating prism (PGP) beam splitter, the 4th, image-forming objective lens, it and collimator objective are in full accord, and the eyeglass of collimator objective and image-forming objective lens distributes axisymmetricly about the PGP beam splitter; The 5th, the picture plane, ccd detector receiving surface just, it and optical axis are 5.32 inclinations of spending.

Fig. 2 is the light path synoptic diagram of above-mentioned spectrum imaging system.Referring to accompanying drawing 2, entrance slit 1 is to get preposition telephotolens to target object imaging (preposition telephotolens does not specifically provide) by spectroscopic system, the diaphragm of system is placed on the grating, object is behind the picture process collimator objective 2 at slit place, the collimated ray of chief ray is on optical axis 6, be incident to PGP beam splitter 3, the light of different wave length separately, 7 is the light of three kinds of different wave lengths of outgoing after the chromatic dispersion beam split, be chief ray is divided into three kinds of different wave lengths on the PGP element light, they focus on the picture plane 5 (ccd detector) through image-forming objective lens 4, realized that magnification is the imaging of 1:1,8,9 and 10 is the chief ray of the light of three kinds of different wave lengths, and they are all parallel with optical axis, satisfy thing, telecentric beam path in image space can uniform irradiation on the ccd detector receiving surface.

Fig. 3 is the structural representation of prism grating prism (PGP) element in the spectrum imaging system that provides of the embodiment of the invention.Referring to accompanying drawing 3; 11 is first (left side) prism; the 12nd, the substrate of grating, the 13rd, body holographic phase grating, grating constant is that every millimeter 588 line is right; the 14th, the cover glass of grating; 15 is second (right side) prism, wherein, and in the middle of body holographic phase grating 13 is positioned at; left side prism 11 is identical with right prism 15 shapes, and distributes axisymmetricly with grating 13.

Among Fig. 3, OO ' is an axis that is parallel to PGP element bottom surface, and with the optical axis of collimator objective and image-forming objective lens on same line.Centre wavelength light is with incident angle β ₁Inciding drift angle along OO ' is β ₁ Prism 11, the refraction angle is θ ₁, then with θ ₂Incident angle to grating 13, the angle of diffraction of emergent ray is θ ₃, and with incident angle θ ₄Be incident to the inclined-plane of prism 15, the drift angle of prism 15 is β ₂, at last with refraction angle θ ₅Outgoing, prism 11 and 15, grating substrate 12 and cover glass 14 are the glass of commaterial, and its refractive index is n.If make emergent ray still on optical axis, need satisfy condition:

θ ₅＝β ₂ (1)

According to refraction law, the relational expression below incident angle on the two prisms dip plane and emergence angle satisfy:

sinβ ₁＝nsinθ ₁ (2)

nsinθ ₄＝sinθ ₅ (3)

According to triangle geometric relationship (being illustrated in fig. 2 shown below), the angle on grating G incident angle and angle of diffraction and the prisms tilted face has following relational expression (4) and (5):

θ ₁＝β ₁-θ ₂ (4)

θ ₄＝β ₂-θ ₃ (5)

Can get by conversion (2)-(5) formula:

nsin(β ₂-θ ₃)＝sinβ ₂ (6)

sinβ ₁＝nsin(β ₁-θ ₂) (7)

Body holographic phase grating is non-inclination transmission grating, and the propagation vector of grating is parallel with the glue face, therefore as incident angle θ ₂With diffraction angle ₃Diffraction efficiency maximum when equating, promptly satisfy Bragg condition and obtain:

${\mathrm{\θ}}_2={\mathrm{\θ}}_3=\arcsin \frac{{\mathrm{\λ}}_C}{2d}---\left(8\right)$

Wherein d is a grating frequency, λ _CBe centre wavelength.

Can release by above-mentioned formula (6), (7) and (8) again:

$\sin {\mathrm{\β}}_1=n\sin ({\mathrm{\β}}_1-\arcsin \frac{{\mathrm{\λ}}_C}{2d})---\left(9\right)$

β ₁＝β ₂ (10)

PGP component parameters β ₁, β ₂Just can be by glass refraction n, grating constant d and central wavelength lambda _CDetermine.The width d of prism ₁, d ₂Directly do not concern with the direct-view of light, get appropriate value and get final product.The light of centre wavelength light behind the PGP+1 order diffraction has kept the alignment of optical system still on optical axis.

The concrete structural parameters of the spectrum imaging system that present embodiment provided are referring to table 1.

The object space numerical aperture of system is 0.19, and linear field is 7.6mm, and magnification is 1:1, and operation wavelength is in 420～760nm scope.Employed in the system all is homemade glass.The length of system is less than 85mm, and maximum effective aperture is 15mm, is coaxial optical system, and whole shape is as a pen.

Fig. 4 is that optics gets the trace point range figure by the described optical system of present embodiment, the light that is entrance slit is through receiving as the focusing situation on the plane behind the spectrometer, among the figure, different wave length (420nm, 585nm, 760nm) the point range figure situation that (0mm, 2.7mm, 3.8mm) locates in different visual fields, the size of a pixel of the used CCD of each box indicating is 15 microns * 15 microns, as seen from Figure 4, the light of locating as each visual field of different wave length on the plane all focuses in pixel of CCD, shows that this optical system has imaging characteristic preferably.

Referring to accompanying drawing 5, it is the encircled energy curve of the described optical system of present embodiment, and as seen from Figure 5, the concentration of energy more than 85% is in pixel of CCD.

Referring to accompanying drawing 6, it is the relative radiant illumination scatter chart of the described optical system of present embodiment on receptor surface, because system has preferably the disposition far away as the side, as can be seen from the figure, illuminance of image plane distributes very even.

Referring to accompanying drawing 7, it is that the described optical system of present embodiment gets the modulation transfer function curve, and as seen from the figure, this spectrometer more than 0.8, has imaging performance preferably in the transfer function values at selected detector nyquist frequency place.

Table 1:

The face sequence number	Radius/mm	At interval/mm	Material	Other parameters
					OBJ	Infinity	7.964
1	102.652	3.900	ZK11
					2	-11.980	8.314
3	-7.164	5.211	ZF6
					4	41.500	1.620
5	-21.235	2.800	LAF1
					6	-13.850	1.000
7	-337.479	4.450	ZK11
					8	-14.002	3.600
9	Infinitely great	7.600	K9	Prism vertex angle 18.65 degree
					Stop	Infinitely great			Grating constant 5881p/mm
11	Infinitely great	7.600	K9	Prism vertex angle 18.65 degree
					12	14.002	4.450	ZK11
13	337.479	1.000
					14	13.850	2.800	LAF1
15	21.235	1.620
					16	-41.500	5.211	ZF6
17	7.164	9.000
					18	11.980	3.900	ZK11
19	-102.652	7.155
					IMA	Infinitely great

Claims (5)

1. prism-grating-prism imaging system, it comprises beam splitter, collimator objective and the image-forming objective lens of prism-grating-prism combination, it is characterized in that: described collimator objective is the four-piece type lens structure, wherein, from entrance slit second eyeglass backward is negative power, and its excess-three piece eyeglass is positive light coke; The beam splitter of described prism-grating-prism combination, its body holographic phase grating satisfies Bragg condition, and two prisms on a grating left side and the right distribute axisymmetricly; Described image-forming objective lens is identical with collimator objective, and the eyeglass of collimator objective and image-forming objective lens distributes axisymmetricly about beam splitter; System is 5.0～5.5 inclinations of spending as plane and optical axis, and the diaphragm of system is placed on the grating, satisfies thing, telecentric beam path in image space.

2. a kind of prism-grating-prism imaging system according to claim 1 is characterized in that: the holographic phase grating constant of described body is that every millimeter 500～600 line is to scope.

3. a kind of prism-grating-prism imaging system according to claim 1 is characterized in that: its object space numerical aperture is 0.19, and linear field is 7.6mm, and magnification is 1:1.

4. a kind of prism-grating-prism imaging system according to claim 1 is characterized in that: its operation wavelength is in 420～760nm scope.

5. a kind of prism-grating-prism imaging system according to claim 1 is characterized in that: its length dimension is less than 85mm.

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