Interesting astronomical papers from SPIE Optical Engineering and Applications conference 2011

More about papers from the SPIE conference; main section about the adatpvie optics was on Sunday, but some other interesting posters were in other days as well. 

Advancements in laser tomography implementation at the 6.5m MMT,  . . . .[8149-07]

The system on the MMT uses 5 LGS stars, 336 voice-coil actuators and they trying to use dynamics focus. The LGS they use is sodium beacon, and, as it is well known fact, the sodium LGS tends to elongate.

They capture everything on one CCD - this means that all of LGS on one CCD. They also use the WFS instrument for the NGS light from tip-tilt star (to sense the tip/tilt distortion).

Least-squares LTAO implementation uses SVD decompostition (modal decomposition) for tomographical reconstruction. Wind can be detected from multiple LGS beacons. They obtain then a tomographic matrix.

However, the problem with the SVD is computationally intensive algorithms.

The further challenges are presented on the slide above.

Wavefront control with SCExAO: concepts and first on-sky results,
Olivier Guyon, Frantz Martinache, Christophe Clergeon, Robert Russell, Subaru Telescope, National Astronomical Observatory of Japan (United States); . . . . . . . . . . . .[8149-08]

The paper presents a wavefront control on the Subaru telescope. They use phase induced amplitude apodizer (PIAA) - a novel concept that can be used for the coronography.

The PIAA is used for the redistribution of light without loss. They try to decrease the speackles using the PIAA.

A sensitivity comparison between the non-linear curvature wavefront
sensor and the Shack-Hartmann wavefront sensor in broadband, Mala Mateen,  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .[8149-09]

This was a really strange presentation. The promising title was ruined by poor presentation: out of slides it was impossible to understand the point.

They tried to compare Curvature WFS that measures:

\[ C = \frac{W_+ - W_-}{W_+ + W_-}

They observed Talbot effect:

Talbot imaging is a well-known effect that causes sinusoidal patterns to be reimaged by diffraction with characteristic period that varies inversely with both wavelength and the square of the spatial frequency. This effect is treated using the Fresnel diffraction integral for fields with sinusoidal ripples in amplitude or phase. The periodic nature is demonstrated and explained, and a sinusoidal approximation is made for the case where the phase or amplitude ripples are small, which allows direct determination of the field for arbitrary propagation distance.

[from the paper: Analysis of wavefront propagation using the Talbot effect
Ping Zhou and James H. Burge, Applied Optics, Vol. 49, Issue 28, pp. 5351-5359 (2010)       doi:10.1364/AO.49.005351 » View Full Text: Acrobat PDF (785 KB) ]

Image plane phase-shifting wavefront sensor for giant telescope
active and adaptive optics, François Hénault, Univ. de Nice Sophia Antipolis (France) . . . . . . . . . . . . . . . . . . . . . . . . . . . .[8149-10]

The paper is about phase shifting WFS, although the speaker was not very detailed in descriptions.

The thing is, they use it for making a cross-spectram measurements.