Knowledge of the refractive index structure constant profile at an astronomical site is crucial before developing a Multi-Conjugate Adaptive Optics (MCAO) system at that site. The S-DIMM+ (S-Differential Image Motion Monitor+) method proposed by Scharmer and van Werkhoven uses the images recorded by a SHWFS (ShackHartmann Wavefront Sensor) to estimate the profile. We have performed simulations of the same using simulated solar granulation images (which are the “objects”) and multiple layers of the atmosphere characterised by Kolmogorov turbulence, a telescope of given aperture and finally a SHWFS. The images formed using the SHWFS are then processed using an inversion code developed by us to get the turbulence strength profile. We found that the code was able to invert the data satisfactorily upto a height of 10 km with our system parameters.
Spatial Heterodyne Spectroscopy (SHS) is a relatively novel interferometric technique similar to Fourier transform spectroscopy and shares design similarities with a Michelson Interferometer. An Imaging detector is used at the output of a SHS to record the spatially heterodyned interference pattern. The spectrum of the source is obtained by Fourier transforming the recorded interferogram. The merits of the SHS -its design, including the lack of moving parts, compactness, high throughput, high SNR and instantaneous spectral measurements - makes it suitable for space as well as ground observatories. The small bandwidth limitation of the SHS can be overcome by building it in tunable configuration (Tunable Spatial Heterodyne Spectrometer(TSHS)). In this paper, we describe the wavelength calibration of the tunable SHS using a Halogen lamp and Andor monochromator setup. We found a relation between the fringe frequency and the wavelength.
Spatial heterodyne spectroscopy (SHS) is an interferometric technique similar to the Fourier transform spectroscopy with heritage from the Michelson interferometer. An imaging detector is used at the output of an SHS to record the spatially heterodyned interference pattern. The spectrum of the source is obtained by Fourier transforming the recorded interferogram. The merits of the SHS—its design, including the absence of moving parts, compactness, high throughput, high SNR, and instantaneous spectral measurements—make it suitable for space as well as for ground observatories. The small bandwidth limitation of the SHS can be overcome by building it in tunable configuration [tunable spatial heterodyne spectrometer (TSHS)]. We describe the design, development, and simulation of a TSHS in refractive configuration suitable for optical wavelength regime. Here we use a beam splitter to split the incoming light compared with all-reflective SHS where a reflective grating does the beam splitting. Hence, the alignment of this instrument is simple compared with all-reflective SHS where a fold mirror and a roof mirror are used to combine the beam. This instrument is intended to study faint diffuse extended celestial objects with a resolving power above 20,000 and can cover a wavelength range from 350 to 700 nm by tuning. It is compact and rugged compared with other instruments having similar configurations.
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