Astrophotonic technologies, specifically mass-produced “spectrometers-on-a-chip,” offer an exciting path toward dramatically reducing the cost-per-spectrum of astronomical spectrographs. This technology could one day enable significant multiplexing upgrades to fiber-based instruments and inspire new facilities capable of collecting 100,000 simultaneous spectra in both single-fiber and IFU formats. Here, we report on a new astrophotonics platform at Lick Observatory for on-sky testing of such technologies. Our initial focus is on the problem of efficiently coupling telescope light into photonic devices, which are typically optimized to work with a single mode, i.e., with diffraction-limited light. While photonic lanterns can deliver multiple single-mode outputs given multi-modal input, here we introduce the concept of Adaptive Mode Extraction (AME), which uses a second, reference lantern to select the brightest instantaneous mode or modes for injection into photonic devices. Analogous to “speckle spectroscopy,” this technique has the potential to increase the signal-to-noise ratio for faint sources by spatially filtering out the sky background. We have deployed our testing platform behind the AO system at the Shane Telescope and demonstrate that it meets requirements for our planned on-sky tests of AME, namely the ability to couple AO-corrected light from two nearby stars (within 2′′) into two dynamically-positioned lanterns, with adequate throughput (<40%) and image quality (0.15′′).
The large distance between Earth and other planetary systems makes it so that exoplanets appear as point sources to our telescopes. This is in stark contrast to the appearance of our own solar system planets, which range in angular diameter from a few arcseconds to arcminutes. Their relatively large projected size on the sky allows for detailed analysis of planetary features such as rings, atmospheric and cloud features, and more. The Planet as Exoplanet Analog Spectrograph (PEAS) instrument at Lick Observatory is designed to simulate exoplanet observations and analysis techniques using disk integrated observations of the solar system planets. PEAS uses an integrating sphere to spatially scramble the light from the planet and take a spectrum of the entire visible surface. PEAS observations of solar system planets can then be used as benchmarks for testing and validating exoplanet observations and atmospheric models. In this work, we model the throughput of the PEAS instrument, including the telescope, integrating sphere, and spectrograph components. We are able to reproduce a PEAS spectrum to within a factor of 10. We then model the throughput with possible upgrades to the system and determine which new components would produce the best efficiency.
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