WO2013017458A1

WO2013017458A1 - Echelle spectrometer

Info

Publication number: WO2013017458A1
Application number: PCT/EP2012/064410
Authority: WO
Inventors: Hans-Jürgen DOBSCHAL; Jochen Müller
Original assignee: Carl Zeiss Microscopy Gmbh
Priority date: 2011-08-02
Filing date: 2012-07-23
Publication date: 2013-02-07
Also published as: DE102011080278A1

Abstract

An echelle spectrometer is provided, comprising a detector (3) and a monolithic transparent body (2), which has an entry area and an exit area on a front side (4) of the body (2) and a reflective echelle grating (6) on the rear side (5) of the body (2), wherein a beam (S) entering the body (2) via the entry area is reflected at the echelle grating (6) to the exit area and is thereby spectrally split in a first dispersion direction (D1), passes through the exit area and impinges on the detector (3), the body (2) being designed so as to provide a dispersing effect for the beam (S) entering via the entry area, reflected at the echelle grating (6) and exiting via the exit area in such a way that a separation of the orders of diffraction of the echelle grating (6) takes place transversely in relation to the first dispersion direction (D1).

Description

Echelle spectrometer

The present invention relates to an echelle spectrometer. Echelle spectrometers are usually used in areas where a spectrum with a large wavelength range is to be detected in high resolution at once. Particularly in the field of analytical chemistry in the qualitative and quantitative detection of elements, there is a need for an expansion of the resolvable spectral range while increasing the spectral resolution. Also in the field of astronomy in the recording of star spectra with high resolution Echelle spectrometers are used.

Known echelle spectrometers have an echelle grating for generating a dispersion spectrum and another grating or a dispersion prism in order to separate the partially successive diffraction orders from one another. Therefore, such echelle spectrometers have a variety of discrete optics and mechanical components, so that a high installation and adjustment effort is present and cost-effective production of Echelle spectrometer is not possible.

Based on this, it is an object of the invention to provide an echelle spectrometer which is compact, can be manufactured inexpensively and has good optical performance parameters.

The object is achieved by an echelle spectrometer with a detector and a monolithic transparent body, which has an entrance surface and an exit surface on the front side of the body and a reflective echelle mesh on the back side of the body, wherein a radiation beam entering the body via the entry surface is reflected at the echelle grating to the exit surface and thereby spectrally split in a first dispersion direction, passes through the exit surface and strikes the detector, wherein the body is designed so that it for the incoming via the entrance surface, reflected at the echelle and exiting via the exit surface beam a dispersing effect such provides that takes place transversely to the first dispersion direction, a separation of the diffraction orders of Echellegitters.

Through this monolithic structure, the number of required optical elements is minimized, which on the one hand leads to a significant miniaturization and on the other hand significantly reduces the adjustment and assembly costs. Furthermore, very good optical performance parameters are achieved.

The dispersing effect of the transparent body transversely to the first dispersion direction can be provided by a prismatic formation of the transparent body and its wavelength-dependent refractive index.

Due to the monolithic structure of the transparent body this can by molding, such. As injection molding or injection-compression molding, are produced. As a result, a cost-effective and fast production is possible.

In particular, the echelle grating is designed as an imaging grating. This achieves a further reduction of the optical elements. In the spectrometer according to the invention, the transparent body may be formed so that its prismatic effect can not be assigned a single dispersion direction for all wavelengths and diffraction orders. However, each diffraction order may be assigned a dispersion direction averaged over the wavelength, and thus an average dispersion direction as a second dispersion direction. It is preferred that the average dispersion direction of each diffraction order with the first dispersion direction each include an angle greater than 45 ° and in particular greater than 60 °. In particular, the angle for at least one diffraction order can be 90 °.

Furthermore, the mean dispersion directions of the diffraction orders by z. B. a maximum of 10 ° -20 ° differ. In particular, this difference exists between the mean dispersion direction of the lowest diffraction order and the highest diffraction order of the echelle lattice. The lowest and highest orders of diffraction are understood to be the lowest order of diffraction used and the highest order of diffraction used.

Furthermore, the spectrometer according to the invention can be designed so that the separate diffraction orders of Echelle grid form a continuous spectrum. In particular, the smallest wavelength of a first diffraction order of the Echelle grating of the largest Wavelength of the next higher diffraction order of the echelle lattice correspond. Thus, there is a continuous spectrum over all diffraction orders.

In the spectrometer according to the invention, the beam path of the radiation beam can be folded exactly once from the entrance surface via the echelle grating to the exit surface. This folding is realized by the reflection of Echelle grid. This embodiment contributes to the compact design of the transparent body and thus of the spectrometer.

In the spectrometer according to the invention, the back can be spherically curved, at least in the region of the echelle lattice. It is also possible that the back is formed, at least in the region of the echelle lattice, as a rotationally symmetric asphere or as a non-rotationally symmetric asphere, which may also be referred to as a free-form surface. Also, the front side may be formed in the region of the exit surface as a sphere, as a rotationally symmetric asphere or as non-rotationally symmetric asphere.

The echelle grating is preferably designed as a blazed reflection grating. Since the grating is used as a back grating, a shift in the blaze maximum by about n (n = refractive index of the transparent medium and may be, for example, 1.5) occurs at higher wavelengths, which in many cases has practical applications accommodates. In particular, then for the transparent body, an ordinary glass, such. B. BK7, are used. Of course it is also possible to use quartz or fluorspar for the transparent body. In general, the transparent body can be made of plastic, glass or quartz.

In the spectrometer according to the invention, the detector may have a flat detection area. This makes it possible to simultaneously detect the different diffraction bands spectrally resolved.

Furthermore, in the spectrometer according to the invention, the rear side of the transparent body can be curved at least in the area of the echelle grating in such a way that upon reflection at the echelle grating, the beam is focused in the horizontal and vertical planes. The horizontal plane is preferably the plane in which the first dispersion direction lies.

Furthermore, in the spectrometer according to the invention, the beam can be focused in the horizontal and vertical plane when passing through the exit surface. In particular, can the exit surface can be used to reduce astigmatism and / or spectral field curvature. This is particularly advantageous because the exit surface is positioned close to the image field. The entrance and exit surfaces on the front of the transparent body may be spaced apart or at least partially penetrated. In particular, it is possible that the entrance and exit surface part of the same area, for. B. are the same freeform surface. Of course, alternatively (in particular if the entry and exit surfaces are spaced apart from each other), the entry surface may have a surface shape independent of the exit surface and be optimized separately in order to ensure the best possible optical performance parameters of the spectrometer. In particular, the entry surface may be formed as a flat surface.

The spectrometer according to the invention is designed in particular for wavelengths from the visible wavelength range, ie for electromagnetic radiation having a wavelength in the range of 380-780 nm. Furthermore, the spectrometer according to the invention can additionally or alternatively be designed for the UV range and / or the I R range. So z. B. a wavelength range of 500-900 nm possible. The spectrometer may comprise a housing in which the detector and the transparent body are arranged. The entrance slit can be formed on a wall of the housing.

Furthermore, the entrance slit can be realized, for example, by the exit-side end of an optical fiber.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the specified combinations but also in other combinations or alone, without departing from the scope of the present invention.

The invention will be explained in more detail for example with reference to the accompanying drawings, which also disclose characteristics essential to the invention. 1 is a schematic perspective view of an embodiment of the Echelle spectrometer according to the invention; Fig. 2 is a perspective view of the transparent body of the Echelle spectrometer according to the invention;

Fig. 3 is a side view of the transparent body of Fig. 2, and

Fig. 4 is a schematic representation of the incident on the detector diffraction bands of Echelle spectrometer according to the invention.

In the embodiment shown in FIG. 1, the echelle spectrometer 1 according to the invention comprises a monolithic transparent body 2 and a detector 3.

The body 2 comprises a front side 4 and a back side 5, wherein the front side 4 is aspherical curved and in the back 5 has a spherical curvature. The concave radius of curvature of the back 5 is 73.652 mm.

On the back 5, an imaging Echellegitter 6 is formed, which is here a blazed reflection grating with about 10 to 100 lines per mm. The blaze angle is in the range between 50 ° and 80 °.

In Fig. 1, the course of a beam S, which emanates from an entrance slit 7, shown schematically. The beam S enters through the front side 4 in the transparent body and runs to the back 5, where it is reflected on Echellegitter 6 and in turn runs to the front 4, exits from this and strikes the detector 3. For ease of illustration, the course of the beam S after entry through the front 4 to the back 5 is not shown in Fig. 1. The beam path drawn in the transparent body 2 corresponds to the beam path after reflection on echelle grating 6.

The echelle grating 6 is designed such that upon reflection, a spectral splitting in a first dispersion direction D1 occurs, which is shown schematically in Fig. 2, in which only the transparent body 2 is shown in perspective. The grid grooves of the echelle grating 6 are indicated by the dotted lines 8. In order to separate now the diffraction orders of the echelle grating 6, which at least partially coincide, the front side 4 is curved and arranged relative to the spherical back 5, that the passing through the transparent body 2 beam S with a dispersing action transverse to the first dispersion direction D1 is applied. This is achieved by the prismatic formation of the transparent body 2, which can be seen in FIG. 2 and in particular in the side view of the transparent body 2 in FIG. 3. It is thus achieved that the spectra of the individual diffraction orders impinge separately on the detector 3, as shown schematically in FIG. 4 for the seventh to thirteenth order of diffraction, which are used in the described embodiment and extend from left to right in each case. B _{7 is} the seventh diffraction order, B _{8 is} the eighth diffraction order, ... and B _{13 is} the thirteenth order of diffraction. Since the detector 3 has a flat detection area, it can simultaneously detect the spectra B ₇ -B ₁₃ shown in FIG. 4. The detector 3 can therefore also be referred to as an area detector. Due to the prismatic design of the transparent body 2 and in particular by the curvature of front side 4 and back side 5, the dispersing effect for separating the diffraction orders of the echelle grating 6 can not be assigned a clear dispersion direction. However, one can assign to each diffraction order B ₇ -B ₁₃ a dispersion direction averaged over the wavelengths of each diffraction order. For the seventh diffraction order B ₇ , the averaged dispersion direction D2 (which may also be referred to as the second dispersion direction D2) is perpendicular to the first dispersion direction, such. B. is shown schematically in Fig. 2.

As can be seen in particular from the illustration in FIG. 4, the averaged dispersion directions D2 of the different diffraction orders are different from one another. Thus, the mean dispersion direction of the seventh diffraction order of the average dispersion direction of the thirteenth order of diffraction by z. B. 10 ° -20 ° differ. To simplify the illustration, only the averaged dispersion direction D2 of the seventh diffraction order is shown in FIGS. 2 and 3.

The echelle spectrometer 1 according to the invention is here preferably designed such that the diffraction orders used (here seventh to thirteenth diffraction order) represent a continuous spectrum. The spectrum can z. B. from 500-900 nm run. The bandwidth of each individual diffraction order B ₇ -B ₁₃ corresponds approximately to the mean wavelength A _M i _tt e divided by the diffraction order n. This can be clearly seen in Fig. 4, since with increasing diffraction order, the width (horizontal extent) of the respective diffraction order decreases on the detector 3. The representation in FIG. 4 is chosen so that the wavelength increases from left to right and decreases from bottom to top. Thus, z. For example, the wavelength of the seventh diffraction order on the far left (reference numeral 10) of the wavelength of the eighth diffraction order on the right (reference numeral 1 1). Due to the curved configuration of the rear side 5, the echelle mesh 6, in addition to the dispersing function, still has an imaging function. Further, the front side 4 is designed to realize error correcting functions. In particular, the astigmatism and the spectral field curvature are reduced by means of the front side 4.

The transparent body 2 thus combines four optical functions: two dispersing functions (echelle mesh 6 and prismatic formation between front and back 4, 5), an imaging function (echelle mesh 6) and an error-correcting function (front 4). The front side 4 can be described by the following formula: he ^{2 66}

\ + ^ \ - (\ + k) - c ² r ² j = 2

with j = [(m + n) ² + m + 3n] / 2 + 1 and r = ² + y ² , where the conic constant k = -9.5153 10 ^"1 and all the parameters C _j in the are not listed in the following table, have the value zero:

In the above table, the value is given for each parameter C _j and to which xy polynomial it is assigned. Thus the parameter C _{12 is} 6.5461 10 ^"7 for the polynomial x ³ y. If the vertex of the rear side 4 and thus of the echelle grating 6 is at the origin of coordinates, the front side 4 is +5.5622 mm in the x direction relative to the rear side 5, +3.51 17 mm in the y direction and z + direction in the y direction Spins are offset by -16.7275 mm, with rotations in the order of -25.0104 ° about the x-axis, -16.0487 ° about the y-axis, and -21, 3584 ° around the z-axis , The value of c is equal to the reciprocal of -15.81 14 mm.

Claims

claims

1 . Echelle spectrometer with

a detector (3) and

a monolithic transparent body (2) having an entrance surface and an exit surface on a front side (4) of the body (2) and a reflective echelle mesh (6) on the back side

(5) of the body (2),

wherein a ray bundle (S) entering the body (2) via the entry surface is reflected at the echelle grating (6) to the exit surface and is spectrally split in a first dispersion direction (D1), passes through the exit surface and strikes the detector (3), wherein the body (2) is formed so that it for the entering via the entrance surface, the Echellegitter

(6) reflected and exiting via the exit surface beam (S) provides a dispersing effect such that transversely to the first dispersion direction (D1), a separation of the diffraction orders of Echellegitters (6).

2. A spectrometer according to claim 1, wherein the Echellegitter (6) is designed as an imaging grating.

3. A spectrometer according to claim 1 or 2, wherein the dispersing effect of the transparent body (2) is provided transversely to the first dispersion direction by a prismatic formation of the transparent body (2).

A spectrometer according to any one of the preceding claims, wherein the first dispersion direction (D1) having the mean dispersion direction (D2) of each diffraction order of the echelle grating (6) each includes an angle greater than 45 ° or an angle greater than 60 °.

5. A spectrometer according to any one of the preceding claims, wherein the separate diffraction orders of the echelle grating (6) form a continuous spectrum.

6. Spectrometer according to one of the above claims, wherein the beam (S) is reflected exactly once in the transparent body (2) on Echellegitter (6).

7. Spectrometer according to one of the above claims, wherein the back (5) is spherically curved at least in the region of the echelle mesh.

8. Spectrometer according to one of claims 1 to 6, wherein the rear side (5) at least in the region of the echelle grating (6) is formed aspherical.

9. A spectrometer according to any one of the preceding claims, wherein the front side (4) is curved aspherically.

10. A spectrometer according to claim 9, wherein the front side is formed as a non-rotationally symmetric asphere.

1 1. A spectrometer according to any one of the preceding claims, wherein the echelle grating is formed as a blazed reflection grating.

12. Spectrometer according to one of the above claims, wherein the detector (3) has a flat detection area.

13. A spectrometer according to one of the above claims, wherein the back (5) is curved at least in the region of the echelle grating (6) so that upon reflection at the echelle grating (6) focusing of the beam (S) in the horizontal and vertical plane is effected ,

14. Spectrometer according to one of the above claims, wherein the beam (S) is focused in passing through the exit surface in the horizontal and vertical plane.

15. Spectrometer according to one of the above claims, wherein the exit surface reduces astigmatism and / or spectral field curvature.