Abstract
Image slicing is a powerful technique in astronomy. It allows the instrument designer to reduce the slit width of the spectrograph, increasing spectral resolving power whilst retaining throughput. Conventionally this is done using bulk optics, such as mirrors and prisms, however more recently astrophotonic components known as photonic lanterns (PLs) and photonic reformatters have also been used. These devices reformat the multi-mode (MM) input light from a telescope into single-mode (SM) outputs, which can then be re-arranged to suit the spectrograph. The photonic dicer (PD) is one such device, designed to reduce the dependence of spectrograph size on telescope aperture and eliminate modal noise. We simulate the PD, by optimising the throughput and geometrical design using Soapy and BeamProp. The simulated device shows a transmission between 8 and 20 %, depending upon the type of adaptive optics (AO) correction applied, matching the experimental results well. We also investigate our idealised model of the PD and show that the barycentre of the slit varies only slightly with time, meaning that the modal noise contribution is very low when compared to conventional fibre systems. We further optimise our model device for both higher throughput and reduced modal noise. This device improves throughput by 6.4 % and reduces the movement of the slit output by 50%, further improving stability. This shows the importance of properly simulating such devices, including atmospheric effects. Our work complements recent work in the field and is essential for optimising future photonic reformatters.
Highlights
To detect an Earth-like planet around a Sun-like star or an M-dwarf using the Doppler technique requires sub-m/s radial velocity measurements
Simulations were performed using our produced SOAPY data and real on-sky images acquired in the focal plane at the input of the photonic dicer (PD) provided by CANARY (Myers et al 2008)
In order to match the performance for each adaptive optics (AO) operation mode, the data sets from SOAPY were compared to the corresponding on-sky ones
Summary
To detect an Earth-like planet around a Sun-like star or an M-dwarf using the Doppler technique requires sub-m/s radial velocity measurements. These measurements allow us to probe the Goldilocks zone, detecting the small planets that may harbour life (e.g. Mayor et al 2003; Quirrenbach et al 2016). A dispersive spectrograph is composed of an input entrance slit into which light is coupled from the target. This is collimated by an optic and a dispersive element (e.g. grating or prism) which separates the light chromatically.
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