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Spectroscopy
Published in C. R. Kitchin, Astrophysical Techniques, 2020
Adaptive optics is already used on most large telescopes to reduce the seeing disk size of stellar images and so allow more compact spectroscopes to be used. This approach is likely to spread to smaller instruments in the near future. Direct energy detectors such as STJs are likely to be used more extensively, although at present, they have relatively low spectral resolutions and require extremely low operating temperatures. The use of integral field and multi-object spectroscopes is likely to become more common, with wider fields of view and more objects being studied for individual instruments. The extension of high-resolution spectroscopy to longer infrared wavelengths is likely to be developed, even though this may involve cooling the fibre-optic connections and large parts of the telescope as well as most of the spectroscope. Plus, of course, the continuing increase in the power and speed of computers will make real-time processing of the data from spectroscopes much more commonplace.
Active and Adaptive Optics
Published in Daniel Malacara-Hernández, Brian J. Thompson, Advanced Optical Instruments and Techniques, 2017
Daniel Malacara-Hernández, Pablo Artal
The main advantage of adaptive optics is that astronomical telescopes on the surface of the earth can produce images with a quality only limited by diffraction. In space, where the atmospheric turbulence is absent, the only limitation to the angular resolution of a perfect telescope is diffraction. The angular radius of the Airy disc in radians is θ=1.22λD, where D and l have the same units. In arc-seconds this expression becomes: θ=14D, where D is the objective diameter in centimeters (see Figure 7.6).
A Solution in Search of a Problem or Many Problems with the Same Solution? Applications of Lasers
Published in Mario Bertolotti, The History of the Laser, 2004
Adaptive optics improves the quality of the image provided by large telescopes, by compensating for the aberrations induced by the atmosphere, that is the distortion that it produces on light beams. These distortions are easily seen when one watches, for example, a distant landscape at sunset on a hot, still day when the image appears to tremble. Adaptive optics compensates for these irregularities and sometimes is defined as ‘the technology that stops stars twinkling’ a definition that may generate the horrified reaction ‘It is terrible and should not be allowed!’
Signal-to-noise ratio with adaptive optics compensation in non-Kolmogorov weak turbulent atmosphere
Published in Waves in Random and Complex Media, 2021
Yalçın Ata, Yahya Baykal, Muhsin Caner Gökçe
Inserting Equation (10) into Equation (3) and taking the integral over the vector again by using Equation (9), the signal power in the presence of the atmospheric turbulence with aperture averaging effect becomes Note that the signal power in the absence of the turbulence can be found by taking the coherence length as in Equation (11). Turbulence effect is mitigated when adaptive optics correction is utilized. Therefore, the coherence length in Equation (11) will change with the adaptive optics correction hence the intensity will increase. However, in practice when is kept larger than 15–20 dB in Equation (1), power change is quite limited compared with the . That’s why, neglecting the beam spread and wander, the term in the denominator of Equation (1) is close to unity and stands quite small compared to the term in the denominator of Equation (1). This analysis is given in Reference [40] in detail. In our analysis which is based on larger than 15–20 dB, we did not include the adaptive optics correction effect on the received power whose effect is quite limited compared to .
M-ary pulse position modulation performance with adaptive optics corrections in atmospheric turbulence
Published in Journal of Modern Optics, 2020
Yalçın Ata, Muhsin C. Gökçe, Yahya Baykal
Adaptive optics technologies first introduced in astronomy and medicine have also found use in free-space optical communications as a method of reducing the wavefront distortions at the receiver thereby improving system performance. Many researchers are currently addressing adaptive optics as a solution to improve the performance of OWC systems. The presence of turbulence results in scintillation thereby impairing the OWC system performance; applying adaptive optics correction methods to the receiver can result in an increase in the performance of OWC systems when measured in terms of BER. Fried statistically defined and calculated the wavefront deformation of optical systems due to atmospheric turbulence [1]. Noll expanded Fried’s study and reviewed the Zernike polynomials to wavefront correction in the turbulent atmosphere and showed that optimum correction can be done by using a set of orthonormal functions [2]. The spatial and temporal characteristics of turbulence-induced wavefront distortion were analysed and the effect of turbulence outer scale on adaptive optics was examined in [3]. Sasiela used adaptive optics to correct phase distortion of a collimated wave for the piston removed and piston-tilt removed modes [4]. The adaptive optics correction effect on scintillation was studied for the laser beam in atmospheric turbulence [5], Gaussian beam in non-Kolmogorov atmospheric turbulence [6], in oceanic turbulence [7] and ground to space laser communication [8]. BER performance after adaptive optics compensation for coherent laser communication [9], orbital angular momentum (OAM) beams [10], on–off keying (OOK) and amplitude shift keying (ASK) [11] were also examined in a turbulent medium. Performance of adaptive optics in free-space optical communication systems employing OOK and PPM was simulated and measured in a laboratory-based experiment for Kolmogorov turbulence [12]. All these studies show that adaptive optics correction at the receiver side decreases the scintillation and BER thus improves the OWC system performance. Increasing the removal of the number of Zernike modes enhances the adaptive optics correction effect.