Building a Czerny-Turner optical spectrometer

This project presents the design, construction, and quantitative characterization of a custom asymmetric Czerny–Turner (CT) optical spectrometer for studying the spectral composition of diverse light sources. Building upon optical simulations and design work completed in a prior semester, this phase focused on physical assembly and experimental validation. The optomechanical layout employs two 15◦ off-axis parabolic mirrors with focal lengths of f = 381 mm to eliminate spherical
aberration and suppress first-order coma, following the Shafer criterion for symmetric focal length geometries. A custom rotatable two-grating mount enables rapid, alignment-preserving switching between a 300 lines/mm grating for broad spectral surveys and a 1200 lines/mm grating for highresolution atomic line analysis. The dispersed signal is acquired via a Thorlabs DCC1645C-HQ color CMOS detector coupled with an optimized plano-convex relay lens system that provides a
demagnification factor of approximately M ≈ 0.11 to compress the extended focal spectrum onto the 4.6 mm sensor array.

A custom Python pipeline interfaces with the thorlabs_tsi_sdk for camera communication, frame acquisition, vertical pixel binning across a defined region of interest, and second-order polynomial wavelength calibration via matrix inversion against known atomic emission lines. Initial experiments successfully produced the broadband spectrum of white light, and spectra from multiple lasers, LEDs, and gas discharge lamps were subsequently recorded. Wavelength calibration, resolution analysis via full-width at half maximum (FWHM) measurements, and basic quantitative spectrometric identification were performed.