Absolute Linear-in-K Spectrometer Using Freeform Optics

We present an optical design method and solutions of linear-in-k spectrometers exhibiting extremely low residual nonlinearity (< 10E-4%) made possible by the inclusion of a freeform optics. Previous work in the literature shows that hardware-based solutions for k-linearization by adding a prism after the grating have residual non-linearity. The merit of the linearization was experimentally proven by both the disuse of post k-interpolation and the SNR gain. We found from our simulation that the residual nonlinearity after the k-linearization with a prism can degrade the axial FWHM with depth when no post kinterpolation is performed during the FFT. The roles of the freeform optics are twofold; (1) to reduce the residual nonlinearity common in linear-in-k spectrometer to less than 10E-4% (2) to correct the field-dependent aberrations. In comparing image performance to the conventional approach of a benchmark spectrometer adopting a post k-interpolation, freeform solutions show 29.5 dB SNR gain at the maximum imaging depth of 5.8 mm in air and about 4.25 micron FWHM axial PSF throughout the depth. Freeform optics in linear-in-k spectrometers may be transmissive or reflective. The freeform approach constitutes a milestone in the pathway to next generation linear-in-k spectrometers.

URV Reference Number: 2-19030
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Curtis Broadbent
Licensing Manager
University of Rochester
Jannick Rolland
Aaron Bauer
Changsik Yoon