Search

The temperature dependence of the thermally averaged collisional removal cross section of OH (X 2∏, v=10) by O2, N2O, and CO2 is measured between 220 and 310 K using a two-laser pump–probe technique and a specially designed vacuum-isolated flow cell. OH molecules are generated in v=6–9 by the reaction of hydrogen atoms and ozone. The (10,7) vibrational transition is excited with pulsed near-infrared laser light to create a population of OH (v=10) molecules. The temporal evolution of the v=10 population is monitored as a function of collider gas pressure by a time-delayed ultraviolet laser pulse. The probe step uses laser-induced fluorescence by exciting the B 2∑+–X 2∏ (0,10) transition and detecting the fluorescence from the B 2∑+–A 2∑+ (0,6–8) transitions. From 310 to 223 K, the OH (v=10) removal cross section increases by 35±21, 33±14, and 58±48 percent for the colliders O2, N2O, and CO2, respectively. This inverse temperature dependence is typical of a loss mechanism governed by long-range attractive f...

The solar H Lyman-α line is, through O2 photodissociation, an important source of O(1D) production throughout the mesosphere and lower thermosphere. To ascertain the energy balance in this altitude region, it is necessary to know the O(1D) yield across the solar H Lyman-α feature, since H Lyman-α absorption by O2 at ∼80 km accounts for a substantial fraction of the solar radiation absorbed in the mesosphere. An earlier laboratory study had provided a value of 0.44±0.05 for the O(1D) yield at the center of the solar H Lyman-α line, where the profile shows a minimum in intensity due to strong self-reversal of the line. Using tunable laser radiation, we have determined the O(1D) yield from O2 photodissociation across the entire H Lyman-α profile from 121.2 to 121.9 nm, at a spectral resolution of 0.0015 nm (1 cm−1). The results reveal a strongly wavelength-dependent window in the O(1D) yield, the origins of which are explained using calculations based on a coupled-channel Schrodinger-equations model of the O...

Removal rate coefficients for NO(B 2Π) in the v=2 and 3 levels are measured at 230 K for seven colliders: NO, N2O, CO2, O2, N2, Ar, and He. These measurements are the first below room temperature and are compared to earlier 295 K measurements. These NO(B 2Π) vibrational levels differ from each other in that the v=2 level is unperturbed, and the v=3 level is significantly perturbed by the v=12 level of the a 4Π state. Although there are large variations in removal rate coefficients between the two B 2Π vibrational levels, the effect of reducing the temperature on the removal rate coefficients is modest, the largest effects occurring with the least effective colliders, He and Ar.

The Gemini Planet Imager (GPI) is a facility instrument under construction for the 8-m Gemini South telescope. This paper describes the methods used for optical alignment of the adaptive optics (AO) bench. The optical alignment of the off-axis paraboloid mirrors was done using a pre-alignment method utilizing a HeNe laser and alignment telescopes followed by a fine-tuning using a Shack-Hartmann wavefront sensor and a shear plate. A FARO arm measuring system was used to place the fiducials for the alignment. Using these methods the AO bench was aligned to 13nm RMS of wavefront error. © 2012 SPIE., Modern Technologies in Space- and Ground-Based Telescopes and Instrumentation II, July 1-6, 2012, Amsterdam, The Netherlands, Series: Proceedings of SPIE; no. 8450

The success of the high resolution nightglow studies conducted with the Keck telescopes on Mauna Kea and the Very Large Telescopes in Chile led to the design of the Compact Echelle Spectrograph for Aeronomical Research (CESAR). This is an echelle spectrograph with grating post-dispersion that will be dedicated to nightglow studies at high spectral resolution (R ~ 20000) between 300-1000 nm, and that will be easily deployable at different sites. The development of CESAR is conducted by SRI International, and INO is involved in the optical design and integration of the spectrograph camera, whose all-spherical form is based on the camera of the HIRES spectrograph at the Keck I telescope. The detailed optical design is used to calculate the position of the spectral elements on the detector, predict their image quality, and estimate the level of stray light. This paper presents the methodology used in these analyses.

Coupling of optical signal into a single mode waveguide has been a difficult problem for a long time. An advanced fibre coupling device (AFCD) is a high performance fibre coupling system that provide wavefront correction, vibration isolation and alignment. We will discuss two AFCD, one for a ground to space communication link an a second for astronomical interferometric application (DARWIN and VLTI interferometer).

We present three designs and tolerances of wide-field imagers (30'30 arc-minutes or larger) for astronomical surveying. Two infrared cameras (CPAPIR and PANORAMIX II) were designed for the 0.8-2.4 μm band and a third one (WIRCAM) for the visible and near-infrared band extending from 410 nm to 950 nm. The cameras are installed on the telescopes of the Canada-France-Hawaii (Hawaii, USA) and Mont Megantic Observatories (Quebec, Canada). The three cameras are compact, use only spherical refractive components and have an internal pupil accessible for insertion of filtering components. A Lyot stop must be used in the infrared camera for background rejection. For PANORAMIX II, a set of filters is used at the internal pupil. Correction of the large off-axis aberrations generated by the telescopes, wide spectral coverage, material choices, cryogenic temperature and alignment were the main design challenges. Also, tolerancing was particularly critical for the infrared cameras because they are cryogenically cooled, thus forbidding adjustment of internal components. The cameras’ theoretical performances are presented in terms of point-spread function, encircled energy and distortion.

We present the final design of a wide-field infrared camera to be installed at the Cassegrain focus of the Ritchey-Chretien telescope at the Mont Megnantic Observatory in southern Quebec city. We discussed the cryogenic design technique and the ghost analysis based on Zemax Non-Sequential raytracing.

As part of the Infrared Eye project, this article describes the design of large-deviation, achromatic Risley prisms scanning systems operating in the 0.5 - 0.92 and 8 - 9.5 μm spectral regions. Designing these systems is challenging due to the large deviation required (zero - 25 degrees), the large spectral bandwidth and the mechanical constraints imposed by the need to rotate the prisms to any position in 1/30 second. A design approach making extensive use of the versatility of optical design softwares is described. Designs consisting of different pairs of optical materials are shown in order to illustrate the trade-off between chromatic aberration, mass and vignetting. Control of chromatic aberration and reasonable prism shape is obtained over 8 - 9.5 μm with zinc sulfide and germanium. The design is more difficult for the 0.5 - 0.92 μm band. Trade-offs consist in using sapphire with Cleartran® over a reduced bandwidth (0.75 - 0.9 μm ) or acrylic singlets with the Infrared Eye in active mode (0.85 - 0.86 μm). Non-sequential ray-tracing is used to study the effects of fresnelizing one element of the achromat to reduce its mass, and to evaluate detector narcissus in the 8 - 9.5 μm region.