SU1742634A1 - Spectrograph - Google Patents

Abstract

Use: optical instrument. SUMMARY OF THE INVENTION: The spectrograph comprises a sequential entrance slit, a spherical diffraction grating and a recording device, the grating being installed at a distance d g (1,01056-0.0393 k N N) from the entrance slit and at a distance d gx x 1.0037 -0,014 k AN + 0,058 (k AN) 2 from the recording device; the angle between the segment connecting the center of the entrance slit to the top of the lattice and the normal to the lattice (p -0.016 + 0.748 k AN; the grating lines are curved with a radius of p-3.34 g (k AN) - (0.93 + 0, 72 k AN) y, with a variable distance between them

Description

The invention relates to optical instrumentation, and can be used to create spectral instruments.

Spectrographs are known whose only optical elements are a holographic diffraction grating and a field lens. Such spectrographs contain an entrance slit, a holographic diffraction grating, a field lens and a recording device with a flat receiving surface along the beam. The recording parameters of the holographic grating (type IV according to the looin-Yvon classification) are chosen so that, when operating in a monochromator scheme, astigmatism and meridional coma are minimized.

The disadvantage of this technical solution is that during the operation of the grating in the spectrograph scheme, astigmatism and meridional coma are corrected in a narrow central part of the spectral range. Since modern multichannel receivers used in spectral devices have, in general, a small size of the line height (for example, the height of the photodiode array does not exceed 0.5 mm), astigmatism, increasing

about

with

reaching the edges of the spectrum, significantly reduces the spectrograph luminosity. The spectrograph's luminosity is also limited by the sagittal coma, the value of which increases with increasing relative aperture, which leads to the need to reduce the working shaded surface in the sagittal section, and the lack of minimization of defocus and meridional coma for the entire working spectral range significantly degrades the image quality of the spectrum.

The closest in technical essence to the proposed device is a spectrograph. Such a spectrograph contains an optically coupled entrance slit, a spherical diffraction grating with curvilinear strokes and a variable distance between them, a field lens and a recording device with a flat receiving surface, the diffraction grating is located at a distance of d g (1.01056-0.0393 k AN ) from the entrance slit and at a distance d, 0037-0, 014 k I N + 0.058 (k AN) (di) from the recording device, the angle between the segment connecting the center of the entrance slit to the top of the lattice, and normal to the lattice (f -0,016 + 0,748, curvilinear strokes of the diffraction grating

3.34 performed with radius p - -jTTTT r

- (0.93 + 0.72 k / lN) y, and the variable distance between the strokes satisfies the relation e -jq-1+ (0.12 + 2.7 k N N) x

(3,7-16,3 kAN) 10 Vl. where r is the lattice curvature radius;

N is the frequency of strokes at the top of the lattice;

I is the average wavelength range;

di is the thickness of the field lens;

n is the refractive index of the field lens;

y is the coordinate in the meridional section of the lattice;

k is the working order of the spectrum.

The design parameters of the spectrograph and grating scheme minimize defocusing, correcting astigmatism and meridional coma for wavelengths

h Yat-Yag Ya ± -4-

where I is the average wavelength range;

Yat, Y2 - extreme wavelengths, and the correction in the center of the spectral range of the sagittal coma. The real focal is a circular arc more gentle than the Rowland circle, with a normal coinciding with the direction of the zero beam of the average wavelength range. A lens mounted in front of the focal plane compensates for residual defocusing because wavelengths distant from the center of the spectrogram travel a long way in the glass.

The disadvantages of the spectrograph include the fact that the above ratios provide high image quality, high luminosity in a wide spectral range only for diffraction

lattices with radii of curvature close to 1000 mm, which significantly reduces the functionality of the device, does not allow obtaining high image quality for more compact schemes, and also does not give

the ability to obtain a higher dispersion at high quality of the image of the spectrum by increasing the radius of curvature of the lattice,

In addition, when using radiation-sensitive receivers as receivers of radiation, there is no need to install a field lens, since receivers can also be installed on a curved surface, which simplifies the optical design of the device.

The purpose of the invention is to increase the dispersion and increase the resolution in a wide spectral range,

This goal is achieved by the fact that

a spectrograph containing an optically coupled entrance slit, a spherical diffraction grating and a recording device, the grating being located at a distance of d g (1,01056-0.0393 k N N)

from the entrance slit, the angle p between the segment connecting the center of the entrance slit with the vertex of the lattice, and the normal to the lattice p -0,016 + 0.748 k I N, and the strokes of the lattice

are made curvilinear with a radius t chd

p - r - (0.93 + 0.72 k RN) -y and with a variable distance e satisfying

nineteen

condition e -jq- (1 + jwy + vy), where r is the radius

lattice curvature; N is the frequency of strokes at the top of the lattice; I is the average wavelength of the spectral range; k is the working order of the spectrum; y is the coordinate in the meridional section of the lattice; fi, the coefficients of the nonuniformity of the lattice spacing, the coefficients //, g the nonuniformity of the lattice spacing, -.: m80r conditions m / i, (0.012 + 0.27 k I N) / r + v (0.037-0.163 kAN) / r2, s distance d1 from

lattice to the recording device - condition

o, 0037-0.014 kA N + 0.058 (kAN) 2.

FIG. Figure 1 shows the optical layout of the spectrograph; in fig. 2 - spherical diffraction grating.

The spectrograph contains an entrance slit 1 successively located along the beam, a spherical diffraction grating 2 having a radius of curvature r and located at a distance d g (1.01056-0.0393 kA N) from the entrance slit 1, the surface 3 of the recording device 4, located at a distance d, 0037-0.014 k A N + 0.058 (k AN) 2 from diffraction grating 2 for wavelength A. Angle p between the segment connecting the center of the entrance slit 1 with the top of the grating 2 and the normal to the grating 2 p - -0.0166 + 0.748 k A N. The strokes of lattice 2 have a radius of curvature determined from the expression / e -3.34 r / k A N- (0.93 + 0.72 kA N) y, and DRA between the alternating strokes and satisfying the relation

e - jq - 0,012 + 0.27 k AN) y / r + (0.037 - O 163 k ANjyVr2.

The device works as follows.

Radiation from the entrance slit 1 falls on a spherical diffraction grating 2 at an angle of p −0.0166 + 0.748 k AN. Lattice 2 has, in the general case, strokes of radius p ro-Ru and a variable distance between strokes

e -jq- (1 + yuy + vy2),

where / Oo is the radius of curvature of the line at the top of the lattice;

P is the coefficient determining sagittal coma;

/ g is the coefficient determining the focusing in the meridional plane;

v - coefficient characterizing the meridional coma.

The diffracted radiation is focused on the surface of the recorder 3.

The aberrations of a spherical diffraction grating with curvilinear strokes are characterized by a function of the optical path, having the form

v (y, z) -yFo + Fi +

F2 +

Jl 2

F3 +

yz

F4

(one)

(2)

F, -Mi-kANGi, where y is the coordinate in the meridional section of the lattice;

z is the coordinate in the sagittal section of the lattice;

Mi - contains the parameters of the spectrograph scheme, a GI - the parameters of the grating cutting;

01 (3)

G2 1

Ro Sz 2 (s2 - v) / 3;

C4 fr0-P) // Eo2.

(four)

(5) (6)

Equality of zero FI expresses the condition of focusing in the meridional plane, equality to zero FZ - condition of focusing in the sagittal plane, Pz - characterizes the meridional coma and F4 - sagittal coma. By imposing the condition of minimizing defocusing on a plane perpendicular to the zero beam of the average wavelength of the A range for given values, d is not from the center of the entrance slit to the top of the grating angle of the rays on the grating, we obtain the corresponding values of d and q

II1 l.2

 0, where 1 W

of

 0

dA. (7)

ad Ui ds

In general, getting p0. v and P

conditions for the equality of zero to Fa, Fa, and, it is possible to correct the aberrations of the spectrograph for only one wavelength. Studies have shown that, at certain values of the design parameters of the spectrograph scheme, the minimization conditions (7) and the equality of zero Fa and P3 for two wavelengths located symmetrically relative to the center of the spectral range (D ± Ai-Az

-). where a

. ,, average wavelength

The ranges a AI and Ar are the extreme values of the wavelengths of the range, which guarantees small values of these aberrations throughout the entire working spectral range. These conditions are accountable (0m expressions for Mi are of the form sin (pcos ip / 1 cos d rd

sin p cos p

d

55

2 (-v) kJj + AlJL) .o; (8)

1.1, cos p + cos p

T + d + r

kN PO

()

ABOUT)

where p is the angle of diffraction of wavelengths (A +):

r is the lattice curvature radius, N is the frequency of lines at the vertex of the lattice.

With an increase in the relative aperture of the spectrograph, the effect of the sagittal coma on the image quality of the spectrograph increases. The correction of the sagittal coma in the spectrograph is ensured by the fact that the coefficient P characterizing this aberration is determined from the condition that the aberration is equal to zero for the center of the range

 0

(ten)

Ro g ro

Thus, in the spectrograph, the design parameters of the circuit and the grating are chosen such that the spectrum is focused on a plane with a minimum of defocusing and correction of astigmatism, meridional and sagittal coma in the working spectral range.

When using coordinate-sensitive receivers as radiation receivers, residual defocusing is eliminated by installing these receivers at distances df corresponding to focusing in the meridional section of any wavelengths A (working spectral range, Distance df from the top of the lattice to the focusing surface for wavelength AI is determined from the condition of focusing the rays in the meridional plane.

9, cos2yV cos p + cos p

+ df r

cos d

- k AI N /,

where is the angle of wavelength diffraction A). For wavelength A, the distance is determined by

d1, 0037-0.014, 058 (kAN) 2,

When spherical diffraction gratings with 500 and 2000 mm radii of curvature were installed in the spectrograph, the aberrations decreased by more than 100 times.

5Thus, the possibilities of the spectrograph have been expanded due to the possibility of using spherical diffraction gratings with any radii of curvature. This implies the following

10 benefits; a spectrograph with a grating with a radius of curvature of 2000 mm provides twice as much dispersion, the resolution for any value of the radius of curvature of the diffraction grating is significantly improved.

Claims (1)

A spectrograph containing an optically coupled entrance slit, a spherical 20 diffraction grating and a recording device, the grating being located at a distance of d r (1,01056-0,0393kAN) from the entrance slit and the normal to it forms 25 angle p -0,016 + 0,748 kAN with respect to the segment connecting the center of the entrance slit with the vertex of the lattice, and the strokes of the lattice are curved with a radius of p -3.34 g (kAN) - (0.93 + 0.72 kAN) and with a variable distance e-tt- (1 + + / and y + y2), where r is the lattice curvature radius; 35 N - the frequency of strokes in the top of the grid; A is the average wavelength of the spectral range; k is the working order of the spectrum; y is the coordinate in the meridional section of the lattice; / g, V is the irregularity coefficients of the 40 lattice pitch, characterized in that, in order to increase the dispersion and increase the resolution, the spherical diffraction grating is made with irregularity coefficients of the step satisfying the condition // (0.012 + 0.27kAN) / r; v (0,037-0,163 kAN) / r2, 50 and the distance d from the array to the recording device is subject to d1, 0037-0.014 k A N + 0.058 (k A N) 2. 55 Phie.1 Have