Compact orthogonal-dispersion device using a prism and a transmission grating

Background: Spectroscopy was one of the main applications of gratings. Most spectrometers today are based on reflection grating designs, since high quality transmission grating technologies have only matured over the last several years. Conventional cross-dispersion systems are based on the reflection grating. For traditional direct-vision or constant-dispersion grism, both the prism and grating have the same dispersion direction. Methods: This paper presents an orthogonal-dispersion device based on a transmission grating attached to a prism. The dispersion directions of the prism and transmission grating are orthogonal. The analytical expressions for the dispersion of this device are derived in detail. The numerical results and ray-tracing simulations by ZEMAX software are shown. Results: The simulation results show that the spectrum is spread over 5 diffraction orders, m=3 to -1, the non-diffracted order m=0 is straight, and the other orders are curved. Conclusions: The device will be able to provide a compact, small-sized and broadband orthogonaldispersion device that is suitable for the medium resolution spectrometer.