Telescope Optics

The main error sources are noise in the wavefront sensor measurement, imperfect wavefront correction due to the finite number of actuators and bandwidth error due to the finite time required to measure and correct the wavefront error. Other errors include errors in the telescope optics which are not corrected by the AO system (e.g. high frequency vibrations, high spatial frequency errors), scintillation and non-common path errors. The latter are wavefront errors introduced in the corrected beam after light has been extracted to the wavefront sensor. Since the wavefront sensor does not sense these errors they will not be corrected. Since the non-common path errors are usually static, they can be measured off-line and taken into account in the wavefront correction. 

An optical microscope uses lenses at the ends of a hollow tube to magnify an object (Fig. 4.1). The same principle is found in a telescope. Optical microscopes are often used in the range of 5-lOOx, but sophisticated models can magnify image up to l,000x. A light source is used to illuminate the object of study on a platform... 

The laser resonator emits an almost parallel beam of light through a partial transmitting output mirror at one end of the resonator. The beam may then be shaped to a different diameter and divergence by a collimator (telescope) optic. Figure 2 illustrates the beam delivery system. 

Catadioptric Telescope Optical telescope that makes use of both reflective and refractive properties. 

Optical Telescopes. Optical telescopes are designed to gather and focus light that radiates from distant objects. The two main types of optical telescopes are reflectors and refractors. Each type is based on a different principle derived from the physics of light. A third type, a catadioptric telescope, is a hybrid of reflectors and refractors. 

Another important application of infrared gas analysis is for trace analysis, such as for the analysis of a dilute mixture (in the ppm range) or an environmental specimen. In such cases, individual analytes are measured from the high ppb levels to the lO s or lOO s of ppm. For such analyses, extended path lengths are required, and typically multipass gas cells from 1 to 20 m in path length are used. One very specific application is an open-path measurement for ambient air monitoring in manufacturing plants or in toxic waste sites in which no cell is used. Instead, a source and interferometer combination are focused on a remote detection system with the aid of special telescope optics. In such cases, several hundreds of meters of effective path length are used. 

Receiving equipment for aircraft astrophysical investigations in the far infrared has been developed and flown in 1974-1975 on board the AN-30 aircraft. Four types of infrared and submillimeter detectors mainly of photoresistor type are used in the wavelength region from 10 mkm to 1 mm. Thermal background at the detectors is limited by cooled bandpass filters and by optimal matching of the detectors with the telescope optics. The spectral filters used are combinations of quasiresonance metal mesh filters of different structure and Q-factor from 2 to 7 with the Yamada cut-off powder filters. A tunable Fabry-Perot interferometer, a polarimeter for linear polarization measurements and an aircraft 25 cm-telescope are briefly described. 

In beam switching, the telescope acquires total power data at signal and reference positions by repositioning one of the optical components of the telescope system, usually the secondary mirror (see Fig. 3). Since the optical components are usually relatively small, they can be switched and positioned accurately at a rapid rate, often several Hz. This allows for rapid switching between source and reference positions, which often allows for better subtraction of the fluctuating emission from the earth s atmosphere, but is limited by the relatively small reference position offsets attainable with most telescope optics. 

Atomic Spectrometry Aurora Galactic Structure and Evolution INERARED ASTRONOMY INTERSTELLAR MATTER Planetary Atmospheres Solar Physics Stellar Spectroscopy Stellar Structure AND Evolution telescopes. Optical... 

From the ground, the sensitivity of near infrared observations is usually severely limited by the noise from terrestrial sources of photons. At various points in the spectrum, the prime contributors can be molecular trsmsitions pumped by sunlight, thermal emission from species in the atmosphere, thermal emission from the telescope optics, scattered light from the telescope, thermal emission from particulates in the atmosphere (volcanic dust, ice, water droplets, etc.), auroral airglow, and scattered moonlight, to name a few of the brightest candidates. 

Rutten, H. G. J., and M. A. M. van Venrooji 1988, Telescope Optics Willmann-Bell, Inc. Ridunond Viiguda... 

---