![]() Geometrically corrected CZ configurations such as that shown in Fig. However, in an uncorrected PGS there is field curvature that would display defocusing towards the ends of a planar linear diode array. Defocusing should not be a problem in a PGS monochromator used with a single exit slit and a PMT detector. A good example could be the spherical wavefront illuminating mirror M1 in Fig. This reference wavefront is a sphere centered at the image, or a plane if the image is at infinity.įor example: Defocusing results in rays finding a focus outside the detector surface producing a blurred image that will degrade bandpass, spatial resolution, and optical signal-tonoise ratio. It is not within the scope of this document to review the concepts and details of these aberrations, (4) however, it is useful to understand the concept of Optical Path Difference (OPD) when considering the effects of aberrations.īasically, an OPD is the difference between an actual wavefront produced and a "reference wavefront” that would be obtained if there were no aberrations. PGS systems are used off-axis, so the aberrations will be different in each plane. The most significant are astigmatism, coma, spherical aberration and defocusing. PGS spectrometers exhibit certain aberrations that degrade spectral resolution, spatial resolution, or signal-to-noise ratio. It is also possible to design a system that may accommodate very large optics.Ĭzerny-Turner/Fastie-Ebert PGS Aberrations Spherical aberration and astigmatism will remain at all wavelengths. 10 ).Īlthough the two mirrors function in the same separate capacities as the single spherical mirror of the Fastie-Ebert configuration, i.e., first collimating the light source (mirror 1), and second, focusing the dispersed light from the grating (mirror 2), the geometry of the mirrors in the Czerny-Turner configuration is flexible.īy using an asymmetrical geometry, a Czerny-Turner configuration may be designed to produce a flattened spectral field and good coma correction at one wavelength. The Czerny-Turner (CZ) monochromator consists of two concave mirrors and one planar diffraction grating (see Fig. By using an asymmetrical geometry, a Czerny-Turner configuration may be designed to produce a flattened spectral field and good coma correction at one wavelength. The Czerny-Turner (CZ) monochromator consists of two concave mirrors and one planar diffraction grating. ![]()
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