Clive Standley

On-orbit optical performance of the Space Telescope Imaging Spectrograph

The Space Telescope Imaging Spectrograph (STIS) operates from the UV to near IR providing a general purpose, imaging spectroscopic capability. An internal, two mirror relay system corrects the spherical aberration and astigmatism present at the STIS field position. Low and medium resolution imaging spectroscopy is possible throughout the spectral range and over the 25 arcsecond UV and 52 arcsecond visible fields. High resolution echelle spectroscopy capability is also provided in the UV. Target acquisition is accomplished using the STIS cameras, either UV or visible; these cameras may also be used to provide broad band imaging over the complete spectral range or with the small selection of available bandpass filters. A wide selection of slits and apertures permit various combinations of spectral resolution and field size in all modes. On board calibration lamps provide wavelength calibration and flat fielding capability. We report here on the optical performance of STIS as determined during orbital verification.

Development and testing of diffraction gratings for the Space Telescope Imaging Spectrograph

The second servicing mission for the Hubble Space Telescope (HST), scheduled for early 1997, will be the first change in the spectroscopic capabilities of HST since its initial deployment. The Space Telescope Imaging Spectrograph (STIS) is a multipurpose instrument covering the far ultraviolet (FUV) through near infrared spectral range. It acquires spectra at several spectral resolutions, which facilitates observations at many distances and brightnesses. STIS will replace both of the first generation spectrographs, the Goddard High Resolution Spectrograph and the Faint Object Spectrograph. This will allow the addition of a Near- Infrared Camera. STIS required the development and testing of many high quality diffraction gratings, including several very difficult echelles for the FUV. The methods and results of this grating development program are presented. The results serve as a snapshot of industry capabilities for producing high quality spaceborne diffraction gratings.

Space Telescope Imaging Spectrograph detectors and ultraviolet signal-to-noise capabilities

The space telescope imaging spectrograph (STIS) was designed as a versatile spectrograph capable of maintaining or exceeding the spectroscopic capabilities of both the Goddard High Resolution Spectrograph and the Faint Object Spectrograph (FOS) over the broad bandpass extending from the UV through the visible. STIS achieves performance gains over the aforementioned first generation Hubble Space Telescope instruments primarily through the use of large a real detectors in both the UV and visible regions of the spectrum. Simultaneous spatial and spectral coverage is provided through long slit or slitless spectroscopy. This paper will review the detector design and in-flight performance. Attention will be focussed on the key issue of S/N performance. Spectra obtained during the first few months of operation, illustrate that high signal-to-noise spectra can be obtained while exploiting STISs multiplexing advantage. From analysis of a single spectrum of GD153, with counting statistics of approximately 165, a S/N of approximately 130 is achieved per spectral resolution element in the FUV. In the NUV a single spectrum of GRW + 70D5824, with counting statistics of approximately 200, yields a S/N of approximately 150 per spectral resolution element. An even higher S/N capability is illustrated through the use of the fixed pattern split slits in the medium resolution echelle modes where observations of BD28D42 yield a signal-to-noise of approximately 250 and approximately 350 per spectral resolution element in the FUV and NUV respectively.

Optical Metrology for the Filter Set for the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS)

The Hubble Space Telescope (HST) advanced camera for surveys (ACS) employs a wide variety of spectral filtration components including narrow band, medium band, wide band, and far UV (FUV) long pass filters, spatially-variable filters, VIS/IR polarizers, NUV polarizers, FUV prisms, and a grism. These components are spread across ACSs wide field, high resolution, and solar blind channels which provide diffraction-limited imaging of astronomical targets using aberration-correcting optics which remove most aberrations form HSTs optical telescope assembly. In order for ACS to be truly advanced, these filters must push the state-of-the-art in performance in a number of key areas at the same time. Important requirements which these filters must meet include outstanding transmitted wavefront, high transmittance, uniform transmittance across each filter, spectrally structure-free bandpasses, exceptionally high out of band rejection, and a high degree of parfocality. These constitute a very stringent set of requirements indeed, especially for filters which are up to 90 mm in diameter. The development of unique optical metrology stations used to demonstrate that each ACS filter will meet its design specifications is discussed. Of particular note are specially-designed spectral transmissometers and interferometers.

Adaptive optics performance criteria for imaging and laser communications systems

Atmospheric turbulence over vertical paths or long horizontal paths perturbs phase in the pupil of an optical communications receiver, and also can cause severe intensity scintillation. We describe a mathematical method for predicting a bound for these fluctuations by using the Strehl ratio as a criterion for determining the variations in the intensity fluctuations. Derived is the probability function of the instantaneous Strehl ratio, in addition to methods for computing the lower confidence limit. We show how these functions can vary by the degree of partial wavefront correction via adaptive optics.

Adaptive optics with an AOA WaveScope wavefront sensor and an OKOTechnologies membrane mirror

Adaptive Optics Associates (AOA) has recently developed a commercial Shack-Hartmann wavefront senor called WaveScope for use in optical testing and adaptive optics. The sensor head and associated wavefront analysis software are a powerful and highly flexible combination. Wavefront data can be manipulated and displayed using Tk/Tcl commands and AOAs own atomic functions. To demonstrate this over the last month we have integrated a deformable mirror manufactured by OKOTechnologies into WaveScope. All the software necessary to control the mirror and perform closed loop adaptive optics was written in the Tk/Tcl scripting language which ships with WaveScope. The result is a low cost integrated adaptive optics system.