SPIE Optical Engineering and Applications 2011 - presentations from Astromentry section

Some interesting papers from the Astrometry section that held on Wednesday. This is not about the Adaptive optics, but still contains some interesting points.


 

1. Differention Tip-Tilt Jitter.

It is well known fact that the Tip/Tilt is the main source of distrubance in atmospherical seeing. Other distortions to consider are geometrical ones, like cushion/barrel.

Atmosphere is like a prism - it can displace the star position. Advantages of large telescopes are therefore reduced by CDAR noise.

Dynamic distortion calibration using a diffracting pupil: high-precision astrometry laboratory demonstration for exoplanet detection, . . . . . . [8151-29]

They want to create diffraction spikes. 

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.

Finding a problem for the Research

In the July issue of IEEE Spectrum journal, there were a short but interesting article entitled "In Research, the Problem is the Problem". The author of it reflects about some issues of problem finding - that is, how to find a really worthy research question. There are no definite solution, of cource, but the article itself (one page only) is worth to read and think about. Here are some quotes from it (OCRed version is here).

A problem well stated is a problem half solved. -- Inventor Charles Franklin Kettering (1876-1958)

The solution of problem is not difficult; but finding a problem -- there's the rub. Engineering education is based on the presumption that there exists a predefined problem worthy of a solution.



Internet pioneer Craig Partridge recently sent around a list of open research problems in communications and networking, as well as a set of criteria for what constitutes a good problem. He offers some sensible guidelines for choosing research problems:

• having a reasonable expectation of results
• believing that someone will care about your results
• others will be able to build upon them
• ensuring that the problem is indeed open and under-explored.

All of this is easier said than done, however. Given any prospective problem, a search may reveal a plethora of previous work, but much of it will be hard to retrieve. On the other hand, if there is little or no previous work, maybe there's a reason no one is interested in this problem.



Real progress usually comes from a succession of incremental and progressive results, as opposed to those that feature only variations on a problem's theme.



At Bell Labs, the mathematician Richard Hamming used to divide his fellow researchers into two groups: those who worked behind closed doors and those whose doors were always open. The closed-door people were more focused and worked harder to produce good immediate results, but they failed in the long term.



Today I think we can take the open or closed door as a metaphor for researchers who are actively connected and those who are not. And just as there may be a right amount of networking, there may also be a right amount of reading, as opposed to writing. Hamming observed that some people spent all their time in the library but never produced any original results, while others wrote furiously but were relatively ignorant of the relevant literature.