ISSN 0020-4412, Instruments and Experimental Techniques, 2010, Vol. 53, No. 4, pp. 549–552. © Pleiades Publishing, Ltd., 2010. 549 1 1. INTRODUCTION Spectroscopic investigation of the physical param- eters of plasma and other luminous sources is one of the primary diagnostic techniques for the better understanding of the real systems. Atomic transitions with optical wavelengths are regularly used as indica- tors of plasma parameters such as temperature and density in a variety of plasma devices. The needs of our current study in the chemistry-physics of plasma lead to design and build an optical spectrometer efficient enough, while remaining uncomplicated and versatile [1, 2]. Diffraction grating based instruments are a good compromise between cost and instrumental flexibility. The diffraction grating type instruments can be divided into two groups based on wavelength tuning mechanisms, namely, scanning monochromator and spectrograph [3]. The resulting instrument is simple and inexpensive because the major components are all commercially available. The most common Czerny- Turner configuration [4, 5] has advantage over other configuration like Littrow and Fastie Ebert [6]. By using an asymmetrical geometry, a Czerny-Turner configuration may be designed to produce a flattened spectral field and good coma correction at one wave- length. Spherical aberration and astigmatism will remain at all wavelengths. The resolution and spectral bandpass of the instrument can be easily altered to suit a specific experiment by swapping plane reflective dif- fraction gratings or changing the CCD detector. The main component of the spectrometer is dif- fraction grating. Detailed treatments of the theory of the diffraction grating can be found in any standard optics text [7, 8]. When parallel light is normally inci- 1 The article is published in the original. dent on a diffraction grating, one can derive the famil- iar “grating equation”: , (1) where is the wavelength of the diffracted light, and are the angle of incident and diffracted light relative to the grating normal respectively, is the grating con- stant (i.e., the spacing between lines on the grating), and is the diffraction order. A variety of spectral and pixel resolution modes can be provided by combina- tions of CCD and optical components. In this paper, first we describe the technical specifi- cations of the experimental arrangement and wave- length calibration procedure. Then the concepts of spectral and pixel resolution are discussed. λ= θ+ θ (sin sin ) i d m d λ θ i θ d d m GENERAL EXPERIMENTAL TECHNIQUE Investigation of Spectral Resolution in a Czerny Turner Spectrograph 1 H. Mohammadi and E. Eslami Department of Physics, Iran University of Science and Technology Narmak, Tehran, 16846-13114 Iran Received December 14, 2009 Abstract—This article describes a smiple and low-cost Czerny–Turner spectrograph capable to operate in spectral range from approximately 350–900 nm. A sine drive assembly was used for linearizing the wavelength scale. The wavelength and pixel position calibration problem have been solved using light sources with known wavelength emission lines, and a polynomial fitting method to find the relationship between diffraction wave- lengths and pixel numbers. The pixel resolution ~0.015 nm/pixels and FWHM ~0.1 nm at 170 μm entrance slit width are sophisticated enough to serve well in a research laboratory, yet is simple and inexpensive enough to be affordable for educational use. DOI: 10.1134/S0020441210040147 M 2 M 1 CCD PC m = 0 Grating Slit θ 2θ θ θ i θ d ϕ Fig. 1. Optical path in Czerny–Turner spectrograph.