Externally dispersed interferometer testbed diagnosing Keck Planet Finder spectrograph high resolution performance

David J. Erskine; Jerry Edelstein; Edward Wishnow; Erik J. Davies; Martin Sirk; Richard Ozer; Dayne Fratanduono

doi:10.1117/12.2627160

29 August 2022 Externally dispersed interferometer testbed diagnosing Keck Planet Finder spectrograph high resolution performance

David J. Erskine, Jerry Edelstein, Edward Wishnow, Erik J. Davies, Martin Sirk, Richard Ozer, Dayne Fratanduono

Author Affiliations +

Proceedings Volume 12184, Ground-based and Airborne Instrumentation for Astronomy IX; (2022) https://doi.org/10.1117/12.2627160
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Conference Poster

Abstract

We built an externally dispersed interferometer (EDI) testbed for exploring methods of improving high resolution spectrograph performance. We tested the EDI on the Keck Planet Finder (KPF) spectrograph May 11, 2022 measuring a Fabry-Perot (FP) etalon back lit by white light. This is also the first time an EDI has been used to measure a periodic source. The data shows that the EDI is useful for diagnosing the point spread function (PSF) width and shape, in particular the asymmetry of the PSF. This EDI ability comes because EDI can simultaneously measure both the conventional nonfringing spectrum, and the fringing derived spectrum. A conventional spectrograph resolution is limited by slit blur– the EDI resolution is not. A heterodyning effect shifts the fringing sensitivity peak to arbitrarily higher frequency, set by the interferometer delay value, and thus its resolution can exceed the spectrograph used alone. By comparing the Fourier transforms of the two measured signals, we can compare the phase shift changes, which gives information about the small asymmetry of the spectrograph blur, independent of the much larger asymmetry of the FP source spectrum. We show that comparing the phases of the nonfringing and fringing components versus harmonic number in the Fourier Transform is a useful method for measuring the asymmetry in the PSF. We report the first measurements of an EDI measuring a periodic source, which is a Fabry-Perot (FP) interferometer back illuminated by white light. The periodic character of the FP source created spikes in the Fourier transform, which was very convenient for analysis.

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David J. Erskine, Jerry Edelstein, Edward Wishnow, Erik J. Davies, Martin Sirk, Richard Ozer, and Dayne Fratanduono "Externally dispersed interferometer testbed diagnosing Keck Planet Finder spectrograph high resolution performance", Proc. SPIE 12184, Ground-based and Airborne Instrumentation for Astronomy IX, (29 August 2022); https://doi.org/10.1117/12.2627160

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