OEM spectro Catalogue - Horiba

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8 All gratings exhibit some amount of scattered light. The inherently lower scatter of holographic gratings improves the system performance. Concave grating designs have two additional design advantages, with respect to system stray light, over most commercial plane grating designs. First, grating scatter in Czerny Turner and Fastie Ebert designs is collected and focused, by the focusing mirror, toward the exit port. In concave grating designs the grating does not focus its own scattered light into the focal plane. Secondly, rediffracted light is minimized. Rediffracted light is light that is diffracted by the grating and redirected back to the grating a second time (unintentionally of course). When other concave optics (collimating and focusing mirrors) are used in an instrument design it is more likely that light may be rediffracted. Careful design effort is necessary to prevent rediffracted light. Concave gratings are immune from this problem when working at f-numbers greater than f/2 with low groove density (< 600 gr/mm) gratings. point spherical aberration optical coma system point astigmatism spot diagrams from a point chromatic aberration optical system spot diagrams from a point Aberration correction Aberration correction is the most important benefit of concave aberration corrected holographic gratings. To understand the benefit of aberration correction it is important to understand the main aberrations in <strong>spectro</strong>meter designs and their impact on system results. Optical components can create errors in an image even if they are made of the best materials and have no defects. These aberrations can be grouped into several different categories: spherical aberration, coma, astigmatism, and field curvature. The effects of coma, spherical aberration, astigmatism and field curvature can cause degradation of the system’s performance. Some description is necessary for how these aberrations relate to the exit focal plane of a <strong>spectro</strong>meter. coma chromatic aberration spherical aberration astigmatism
Spherical aberration (SA) Spherical aberrations result from the fact that the focal points of light rays far from the optic axis of a spherical lens or mirror are different from the focal points of rays of the same wavelength passing near the center. A spherical mirror does not precisely focus a point to a point. As light rays move further away from the center axis of a mirror, the focal point moves closer to the mirror. A zone of confusion is created in the image plane because of the changing focal point with distance from center axis. This “zone” of confusion prevents the ability to obtain a sharp focused image. SA is difficult to eliminate without the use of aspheric optics. The result of SA is loss of resolution. Imaging performance degrades causing crosstalk from adjacent wavelengths. In aberration corrected designs the concave grating is designed to correct SA. Coma is an aberration resulting from using off axis optics. Coma causes an unsymmetrical spectral line broadening. This broadening leads to resolution losses and stray light. On a detector array, the impact is pixel to pixel crosstalk and loss of resolution. Coma can be corrected in some instruments, at one wavelength, by adjusting the optical geometry. Coma can be corrected at many wavelengths in the concave aberration corrected grating design. Astigmatism (AST) is another aberration resulting from the use of off axis optics. Point sources “grow” in height as the longitudinal astigmatism increases. Longitudinal astigmatism is the result of the tangential and sagittal components focusing in different planes. Astigmatism effects can lead to a 400 micron input fiber (at the input slit position) “growing” to 2 millimeters high at the output focal plane. When using a 0.5 millimeter high array, and the exit focal plane image is 2 millimeters, 75% of the output signal is not measured. This effect leads to loss of system throughput and the limit of detection. b Optical system without (a) and with (b) spherical aberrations. Spherical aberration is caused by different focal points for rays far from the center and others closer to it (b). a 9
Page 1 and 2: Gratings and OEM Division general s
Page 3 and 4: Introduction As a pioneer and world
Page 5 and 6: Spectrometers for OEM applications
Page 7: System light collection capability
Page 11 and 12: Field curvature (FC) is the shape o
Page 13 and 14: Existing proof of concept systems T
Page 15 and 16: VS70-M The VS70-M is a plug and pla
Page 17 and 18: VS140-M The VS140-M is a plug and p
Page 19 and 20: Modular spectroscopy components a s
Page 21 and 22: Slits and optional CMOS or NMOS det
Page 23 and 24: Input: The VS spectrographs can acc
Page 25 and 26: Drive Electronics: These detectors
Page 27 and 28: Imaging compact spectrographs This
Page 29 and 30: Spectrometer comparaison chart comp
Page 31 and 32: H10-34B OEM imaging monochromator B
Page 33 and 34: 70 60 50 40 30 20 10 0 190 240 290
Page 35 and 36: Technical information Before introd
Page 37 and 38: Note that the lower the dispersion
Page 39 and 40: Projection of the grating width on
Page 41 and 42: G= � � d²G area of the source
Page 43 and 44: Information request form If you hav
Page 45 and 46: Fax form For more information or cu
Page 47 and 48: and product lines HORIBA Jobin Yvon

OEM spectro Catalogue - Horiba

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