DD251837B5 - Polychromator for CCD line mapping - Google Patents

Description

that for the long spectral range the polychromator has the following parameters: grating 1

Grid 2 R = I nm = -3,95 grd R = 180.635 mm Ic = nm l _c = 178.965 mm Id = I _D = 180.027 mm r ^: γ = 11.5 grd δ = δ = -6.19 grd Lines = 200 L / mm = 180.26 mm α = -5grd = 177.624 mm L _A = 180 mm = 177,084 mm L _B = 180.147 mm = 11.5 gr ε = Ogrd = 6,196 grd λ range grating 1: 190 ... 370 Lines = 199.7 L / mm Grid 2: 370 ... 550 - Grid diameter 50 nm

For this 1 page drawings

Field of application of the invention

The invention may be used to generate a particular spectral range for imaging on a receiver line in emission and absorption spectrometry as well as in conjunction with other photometric multichannel detectors.

Characteristic of the known technical solutions

It is known that imaging holographic gratings can be corrected for a flat spectral field. In Journ. Opt. Soc. At the. 61 (1971) 1001, the production conditions of such gratings are described. The Handbook of Diffraction Grating's Ruled & Holographic, 1973 uses corrected concave gratings for use in spectrographs and for line, matrix, and other multichannel receivers.

In DE-OS 1948961 suitable for spectrograph imaging grids are given, wherein the term spectrograph does not include a completely flattened image field.

The grids described so far are not adapted to the special features of lines, apart from the quasi-flat image field. In DE-PS 2656119 a Korrektionsverfahren and the production configuration for Bildfeldgeebnete imaging grids are described. The gratings have three wavelengths with vanishing meridional defocus within the spectral correction range, between which the astigmatism disappears at another point, coma I is a linear function of the wavelength, and the dispersion of the spectrum is approximately linearized. Correction degrees of freedom are in particular the angle of incidence, the deflection angle and the inclination angle of the spectrum.

In Optik 64 (1983) 185-189 a correction method for diode line polychromators is given, which is based on two stigmatischsn points in the correction range and strives to minimize Koma I and Il by changing the magnification. The angle of inclination is also a degree of freedom of correction, but the angle of inclination zero is also permitted in accordance with the requirements.

The particular correction requirements of the imaging grids for line polychromators are based on the geometry of the radiation-sensitive elements or the total area. The width of the elements is typically 0.013 to 0.03 mm, the height 0.3 to 1 mm. The dimensioning of the entrance slit is adjusted taking into account the reproduction scale of these dimensions, wherein the width of the entrance slit can also be several element widths. The relatively low entrance slit area also results in the low conductance of the polychromate, which is principally low for a high aperture ratio of the imaging grid.

Due to the small element height, the aberrations in the sagittal direction, in particular the astigmatism, lead to radiation losses and diminution of the photometric measurement accuracy, especially when the radiation losses oscillate as a function of the wavelength.

Image aberrations in the meridional direction reduce the achievable spectral resolution in the usual way and the photometric accuracy in the case of too narrow gap widths and asymmetrical correction profiles. A particular problem with absorption spectroscopy is when the extensions of the correction profile can reduce the maximum measurable absorbance.

Also problematic is the angle of inclination of the spectral plane with respect to the central optical axis in the spectral field of application.

As the angle of inclination increases, the reflection losses on the line surface increase, which have a correspondingly reduced intensity of radiation, particularly in the UV. This creates u.U. more false light in the spectrometer, a deterioration of the signal-to-noise ratio and in absorption spectrometry worse limits for the maximum and minimum extinction. In addition, a large tilt angle brings about a complicated enlargement of the linear dispersion on the line if a larger spectral range is to be accommodated within the line length.

The spectral sensitivity characteristic of the line has a particularly low sensitivity in the UV, which is about 0.2 to 0.1 compared to the maximum in the long-wave VIS. This results in measurement problems. The effect is further enhanced by scattered light from the long-wave VIS in the short-wave UV.

The blaze characteristic is suitable for improving the signal level in the short-wave, but can not fully compensate for this sensitivity loss.

In the case of a non-linear dispersion course, the evaluation computation effort is also increased. Excessive deflection angles on the grating cause an unfavorable efficiency behavior of the grating, which leads to a limitation of the optimum effectiveness range and a smaller maximum effectiveness with considerable polarization fluctuations.

Object of the invention

The aim of the invention is to develop a Bildfeldgeebnetes, imaging, holographic grating, which is adapted to the properties of the line and no longer has the disadvantages of the prior art.

Explanation of the essence of the invention

The invention has for its object to provide a holographic gratings, which satisfies the required by the line geometry values of resolution, astigmatism and diffraction efficiency, in conjunction with the receiver line improved photometric accuracy and in absorption spectrometric applications allows an increased extinction range. Furthermore, the grating should be adapted to the conditions of the simultaneous measurement of spectral regions with a high sensitivity change and the optical signal background ratio should be improved. This object is achieved by a polychromator for CCD line imaging according to the invention in that in the case of the short spectral range, the course of the astigmatism is corrected so that it runs in conjunction with the diffraction efficiency of the grating and the sensitivity of the receiver line so that the energy curve in the spectral range is approximately linear is designed so that the astigmatism in the short-wave UV has a minimum and then steadily increases. The correction-induced half-width for the entrance gap width to zero and Δλ to zero is substantially equal to one element width of the line and has its minimum in the short-wave UV.

The gap between the entrance slit and the spectrum is minimized for coma and astigmatism reduction and the inclination angle of the receiver line is set equal to or near zero degrees if the diffraction angle at the grating is non-zero degrees for all wavelengths and is non-zero degrees if the diffraction angle is zero degrees in Spectrum occurs with the aim that reflected from the receiver line to the grid radiation hits neither the 0th nor 1st order on the photosensitive parts of the element line

 For the first case, a grid with the following parameters is favorable:

R = 180.26 mm а = -5grd Lc = 175.786 mm La = 182 mm L ₀ = 183.49 mm lb = 178 mm У = 11,5grd ε = 3,11 grd δ = -6,19grd λ = 190 ... 370 mm lines = 200 L / mm Grid diameter =

In the case of the long spectral range, ie when the solution just described is no longer applicable, a polychromator with aberration-corrected, holographically generated concave grating is used to solve the problem, which consists of a pair of Konkavgittern which are interchangeable. The grid intended for the UV range is an imaging hologrite produced by the standing wave method and the symmetrical imaging grating provided for the VIS area. This achieves optimum adaptation of the diffraction efficiency to the line sensitivity. The grating angle for both grids should be set up so that a minimum deflection angle or distance between the entrance slit and the receiver line is created. As a result of this splitting of the spectral range and the simultaneous minimization of the grating deflection angle, the image can be subjected to additional suitable optimization of the remaining grating parameters, such as R, L _c , L q, y, δ. La, L _b with the aim of the field flattening, coma and astigmatism reduction in terms of line geometry and sensitivity make favorable.

The UV grating to be used has the maximum efficiency at 220 nm and the maximum of the spectral resolution and minimum astigmatism at 190 nm.

The linearity of the dispersion is improved due to the shorter partial spectral lengths with simultaneous selection of the two grating line numbers in the ratio gi / g ₂ = 1.0025.

In order to reduce the stray light portion, the receiver line is to be aligned so that light reflected back onto the grating can not get back to the photosensitive parts of the receiver line via the 0th or 1st diffraction order.

For this purpose, if the diffraction angle for all wavelengths is # 0 degrees, the receiver line should be set at approximately zero degrees to the principal ray of the mean diffracted wavelength. If the diffraction angle is zero degrees in the spectrum, the line must be tilted so that the sidelight reflected back from the grating does not hit the photosensitive parts of the line.

The solution according to the invention is particularly favorable if the grids have the following parameters

Grid 1 Grid 2

R = 180.635 mm R = 180.26 mm

L _c = 178.965 mm L _c = 177.624 mm

L ₀ = 180.027 mm L ₀ = 177.804 mm

у - 11,5grd у = 11,5grd

δ = -6,19grd δ = 6,196grd

Lines = 200 L / mm Lines = 199.7 L / mm

а - -5grd а = -3.95grd

L _A = 180 mm

L ₈ = 180.147 mm

ε = 0grd wavelength range: grating 1 190 ... 370 mm

Grid 2 370 ... 550 mm Grid diameter: 50 mm

The resolution with this configuration is sO, 2nm, in the UV <0.12 nm, while the astigmatism 2 is 0.1 mm, in the UV <0.05 mm.

embodiment

The invention will be explained in more detail with reference to drawings.

Fig. 1: shows the manufacturing configuration for the grids Fig.2: the application configuration.

Of the two coherent point light sources D; C, which are located at a distance I ₀ or l _c from the vertex of the lattice girder 2, emanating coherent spherical waves and fall at an angle γ or δ to the lattice normal to the photosensitive material coated (not shown) surface of the lattice girder 2, the concave Surface has the radius R. In Fig. 2 is the entrance slit 1 at a distance I _A from the vertex of the lattice girder 2, through the light at the angle α meets the surface normal to the grid and after reflection at the angle β on the receiver line 3, which is located at a distance Ib from the vertex. The receiver line 3 deviates by the angle ε from the right angle to the direction of incidence. One possible solution using interchangeable grids has the following parameters:

Grid 1 182mm Grid 2 R : 178mm R = Lc 3,11 grd Lc = Ld 190-370 πm L ₀ = У ^: 370-550 η ιm У ' δ δ = а α = = 180.26 mm = 179.71 mm = 175,786 mm = 171.553mm = 183.49 mm = 171.0mm = 11.5grd = 11.5grd = -6,19grd = 6.2 grd = -5grd = -3,95 grd Lines = 200 L / mm Lines = 199.7 L / mm La = Lb = ε = Wavelength range: Grid 1 Grid 2

Claims (1)

A CCD line imaging polychromator comprising an entrance and exit slit system, a concave grid lattice girder, and a receiver array, characterized in that the astigmatism is corrected to be along with the illumination efficiency of the grating and the sensitivity of the receiver array, that the energy distribution in the spectral range is approximately linear, that the astigmatism in the short-wave UV has a minimum and steadily increases, that the correction-induced half-width for the entrance slit width approaches zero and is substantially equal to an element width of the receiver line and has a minimum in the short-wave UV, that the distance between the entrance slit and the spectrum is minimal, that the inclination angle of the receiver line is equal or nearly zero degrees, that for the short spectral range the polychromator has the following parameters: R = 180.26mm - <= -5grd L _c = 175.786 mm L _A = 182 mm L _D = 183.49 mm L _B = 178 mm у = 11,5grd ε = 3,11grd δ = -6,19grd λ = 190 ... 370nm Lines = 200 L / mm Lattice diameter = 50 mm _#