From hyperspectral imaging to telluric line attenuation, Photon etc. offers a great number of solutions for wide variety of requirements in astronomical instrumentation.
We offer Hyperspectral Imagers for unrivalled performance and flexibility, OH Suppression Filters for NIR background attenuation, and Tunable Monochromatic Sources for spectrophotometric calibration of filters and instruments, and EMCCD cameras to see galaxies with sensitivity never before achieved.
Photon etc. traces its roots back to the field of astronomy. Our strong understanding of astronomical instrumentation allows us to develop state-of-the-art devices and contribute to any project concerned with the range of UV to IR.
An example of a project is the characterization of GPI coronograph with a near-infrared adjustable source.
The Gemini Planet Imager (GPI) is an astronomical instrument developed by a consortium of institutions (LLNL, AMNH, Université de Montréal, HIA, UCLA, JPL, and UCSC) that was commissioned at Gemini South in 2012. The primary scientific aim of the instrument is to detect young giant planets in nearby star systems. GPI images directly the planets and obtains low-resolution spectroscopy allowing physical characterization of their otherworldly atmospheres. GPI relies on complementary techniques to reveal planets 10 million times fainter than their parent stars; high-order adaptive optics that correct the atmospheric turbulence in real-time, a coronagraph that eliminates 99% of the coherent starlight, an integral field spectrograph that gives a low-resolution spectrum for every field position and data post-processing techniques.
Testing GPI coronagraph
The apodized-pupil Lyot coronagraph used in GPI relies on the interplay that diffraction imposes between the pupil and image planes to efficiently remove coherent starlight (see Figure 1) while revealing faint, nearby, planets. As it is a central part of GPI’s planet-search technique, testing the coronagraph proved crucial to predicting the instrument’s on-sky performances. The American Museum of Natural History built a testbed that replicates GPI’s coronagraph to measure its performances in a controlled environment. This optical table testbed reproduced all key components of GPI’s coronagraph, including half-toned pupil masks and focal plane mask, producing an image of the residual light on an infrared camera. The practical implementation of the testbed involved a beam launcher illuminating, with a collimated beam, a pupil-defining stop on a mirror. This pupil was then re-imaged on a half-toned mask, the coronagraph’s first element.
Finding a light-source for testing the coronagraph proved challenging, as it required three characteristics. First, as coronagraphs are devices that remove light very efficiently, one needs a powerful source for sufficient light to leak out of the device to efficiently measure its performance. In the sky, GPI observes some of the brightest stars with Gemini South Telescope’s 50 m2 collecting aperture. Furthermore, the light source must be collimated as to be focused into a diffraction spot similar to that produced by GPI’s adaptive optics. Finally, as coronagraphs are based on diffraction, their light-rejection efficiency varies with wavelength. One requires a nearly achromatic source that could be tuned across most of GPI’s wavelength domain (astronomical near-IR; 0.95-2.4 µm) to fully characterize its performance.
Many light sources match one or two of these requirements; lasers are strongly collimated and many types of near-IR lasers would be powerful enough for the proposed test, but none is tunable over such a large wavelength domain. Gratings and prism-based monochromators are tunable over a large domain but have neither the power nor the collimated beam required for the coronagraph characterization. Photon etc’s tunable laser source was chosen as combining all three of the above requirements. It was injected into the beam launcher through a monomode fibre and provided a tunable narrow-band (10 nm) light source across the GPI wavelength domain.
Figure 2 illustrates the sensitivity measurements of GPI’s coronagraph across the astronomical H band (1.50-1.80 µm). At the wavelengths it is most efficient (i.e. 1.60 and 1.65 µm), GPI’s coronagraph allows the detection of a source less than a million times fainter than the diffraction core of the unmasked star at a separation of only 0.35”. This would be sufficient to detect a planet only slightly more massive than Jupiter around a 100 million-year-old Sun-like star. This sensitivity will be further increased by an order of magnitude by data processing techniques. The performances at 1.50-1.55 µm are significantly poorer. These results are in agreement with performances predicted by a detailed Fresnel propagation analysis of the coronagraph.