A new method based on dispersion equations is described to express the spectral resolution of an applied charge-coupled device (CCD) Czerny-Turner Raman instrument entirely by means of one equation and principal factors determined by the actual setup. The factors involved are usual quantities such as wavenumber values for the laser and the Raman band, the diffraction grating groove density, the second focal length, the angle between the incident and the diffracted light, and the full width at half-maximum (FWHM) value of the signal on the detector. A basic formula is derived to estimate the spectral resolution of the Raman instrument. An essential feature of the new method is a proposed way to compensate for non-ideality (diffractions, aberrations, etc.) by use of a hyperbola model function to describe the relationship between the width of the entrance slit and the image signal width on the CCD. The model depends on the spectrometer magnification and a diffraction and aberration compensation factor denoted as A. A could be approximated as a constant that can be determined by the experimental method. The validity of the new expression has been examined by measuring the band width of the 1332.4 cm(-1) diamond Raman fundamental band, excited with two quite different wavelengths (a deep ultraviolet 257.3 nm laser line and a visible green 514.5 nm line). A low pressure mercury line at 265.2042 nm also was applied to give further verification of the given expression. A useful method to find true Raman band widths is also provided. A final finding was that the known significant changes in spectral resolution along the Raman shift axis make static recording and synchronous (extended) scanning modes differ significantly with respect to their resolution properties; this feature has been often overlooked in many contemporary works reporting Raman spectra. A reason for this is that many Raman bands are too wide to show the effect.
Bibliographical noteThis paper was published in Applied Spectroscopy and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase/as/abstract.cfm?uri=as-66-9-1034. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
© 2012 Society for Applied Spectroscopy
- device magnification
- diffraction-aberration compensation factor
- Raman band
- Raman shift axis
- spectral resolution
- 04500, Mathematical biology and statistical methods
- Computational Biology
- charge-coupled device Czerny-Turner Raman spectrometer laboratory equipment
- spectral resolution theoretical derivation mathematical and computer techniques
- Equipment Apparatus Devices and Instrumentation
- Mathematical Biology