Precise Throughput Determination of the PanSTARRS Telescope and the Gigapixel Imager using a Calibrated Silicon Photodiode and a Tunable Laser: Initial Results

TL;DR

This paper presents a method using a calibrated photodiode and tunable laser to precisely measure the wavelength-dependent throughput of the PanSTARRS telescope and imager, enabling detailed system calibration without celestial standards.

Contribution

The authors introduce a novel calibration technique employing a tunable laser and photodiode to measure system throughput across the entire instrument at multiple wavelengths.

Findings

Initial throughput measurements show wavelength-dependent variations.

The method accurately characterizes the entire optical system without celestial observations.

Synthetic photometry indicates throughput variations impact photometric accuracy.

Abstract

We have used a precision calibrated photodiode as the fundamental metrology reference in order to determine the relative throughput of the PanSTARRS telescope and the Gigapixel imager, from 400 nm to 1050 nm. Our technique uses a tunable laser as a source of illumination on a transmissive flat-field screen. We determine the full-aperture system throughput as a function of wavelength, including (in a single integral measurement) the mirror reflectivity, the transmission functions of the filters and the corrector optics, and the detector quantum efficiency, by comparing the light seen by each pixel in the CCD array to that measured by a precision-calibrated silicon photodiode. This method allows us to determine the relative throughput of the entire system as a function of wavelength, for each pixel in the instrument, without observations of celestial standards. We present promising initial results from this characterization of the PanSTARRS system, and we use synthetic photometry to assess the photometric perturbations due to throughput variation across the field of view.