Holographic Grating Spectrometers: Wood's Anomalies, Spectral Response Functions, and Their Dependence on Groove Density

Abstract

Presented is a study of plane holographic gratings with sinusoidal groove profiles, focusing attention on the dependence of grating efficiency on groove density. Experimental spectral response curves are given for a number of gratings with different groove densities in an additive-dispersion double monochromator designed for work at visible wavelengths. The Wood's anomalies, both order-passing and resonance type, are characterized in each case. Simple equations are derived for predicting order-passing wavelengths given a fixed angle of deviation between the incident beam and the observed diffraction order. The trend in the strength of the anomalies is compared with theoretical calculations.

Raman intensities and detection limits of geochemically relevant gas mixtures for a laser Raman microprobe

“…The plane holographic gratings (1800 horizontal grooves/mm) are mounted on a single cosecant-bar, wavenumber drive. As expected, the intensities and slopes of the spectral grating efficiency curves are very different for light polarized parallel and perpendicular to the grating grooves, respectively (see, for example, ref 19). In order for the photon efficiency to be high, it is absolutely necessary that the Raman scattered light interacting with the gratings is polarized dominantly perpendicular to the grating grooves.…”

“…Use of a Calibration Lamp. A sensitivity loss at longer wavelengths has to be expected for both the kinds of gratings (see, for example ref 19) and the photomultiplier tube in our instrument. Even if the grating and quantum efficiency curves for the above two components were accurately known to us (not true), an experimental calibration of the quantitative throughput of the entire instrument still is necessary in order to check the additional effects on the spectral efficiencies of the optical components inside and outside of the microscope (see Figure 1).…”

Artifacts in Fluorescence Emission Spectroscopy Related to Wood's Anomaly

“…Among the latter is the so-called Wood's anomaly which relates to variations in the spectral response of monochromator gratings. A discussion of this anomaly, in holographic gratings, has been provided by Malyj and Griffiths (1986). The effect becomes especially significant when grating and fluorophor characteristics cause spectral distortions to fall at or near a fluorescence emission optimum.…”