Czerny - Turner type infrated scanning spectrometer using plane grating (focal length 1 m, F number 10) is designed, fabricated and its performance is tested. Analytic theory of aberration is used to obtain the initial design parameters and to satisfy the flat field condition.
In order to find the optimum configuration of the Czerny-Turner type spectrometer, 16 different rays are traced (4 different wavelengths and 4 different positions on the grating aperture) and the sum of the squares of the transverse ray aberration is minimized by damped least square method. Transverse ray aberration introduced by the collimating mirror is largely compensated by the focusing mirror giving the maximum confusion width of 40 μ which corresponds to the diffraction image width for λ= 2 μ
To find the resolution of the fabricated spectrometer, the doublet mercury emission spectra (3131.56 Å, 3131.84 Å) are examined in 4th diffraction order using the 1 μ blazed grating (590 grooves/mm, size 102 × 102 mm), the experimentally obtained resolution is found to be 0.25 Å, which is approximately treble the value theoretically expected.
From the analysis of the resolution test, it is expected that when the wavelength is longer than 6 μ, resolution is not affected by the geometrical aberration of the spectrometer, since the diffraction effect from the grating aperture is dominant over the aberration broadening.
