A Simple Method of Calibration for Multichannel Spectrograph Using Charge-Coupled Device (CCD) as a Detector for Raman Spectroscopy

A wavelength calibration procedure has been devised for measuring the wavelength in the multichannel spectrograph using a single wavelength of radiation for calibration which can be obtained from commonly available lamps such as mercury spectral lamp, cadmium lamp, sodium lamp and thallium lamp. This wavelength calibration procedure has been incorporated in a multichannel Czerny-Turner type of spectrograph using CCD as a detector developed indigenously. The spectrograph uses a plane grating of frequency 1200 grooves/mm, concave spherical mirror of focal length 0.523 m as a collimating element and concave spherical mirror of focal length 0.5 m as a focusing element. The linear dispersion of the spectrograph varies from 2.519 pixel/ Å to 2.686 pixel / Å. The spectrum is recorded on the CCD array of pixels 1024 × 256. The pixel size is 26 micron × 26 micron. The accuracy of wavelength measurement is found to be about 1 Å. The instrument works in the wavelength region from 4000 Å to 7000 Å. Raman spectrum of benzene has been recorded by irradiating the sample with an intense beam of a diode-pumped green laser (λ= 532 nm) of power variable from 1 mW to 200 mW. The measured values of wavelengths of Raman lines of benzene using the multichannel spectrograph agree well with the values of the Raman lines reported in the literature. The multichannel spectrograph is found to be useful for Raman spectroscopic applications.