In this paper, dynamic liquid surface measurements using non-disturbing technique based on interferogram analysis with
moiré method are described. A sequence of dynamic deformed fringe images can be grabbed by a phase-shifting
interferometer (PSI) and saved on disk rapidly. By Fourier transform, filtering, phase-shifting through virtual grating and
unwrapping these phase maps in 3-D phase space, the shape of a vortex at different times is obtained. Compared with
others traditional methods such as Fourier transform profilometry(FTP) and phase measuring profilometry(PMP), the
method proposed has characteristics of no phase shifting error, simplicity, accuracy, automatic, high speed and relativly
low price. The experimental results show that interferogram analysis with moiré method can deal with the dynamic liquid
surface shape measurement efficiently. Furthermore, it can be used widely in fluid dynamics, chemical, metallurgy and
some other fields.
In phase-shifting metrology, the accuracy of phase measurement is directly affected by the phaseshifting
error, Accurate calibration of phase-shifter is very important if good measurement results are expected. A new
in-line high accuracy phase-shifting calibration method based on Damped-Least-Square algorithm which provides
stable convergence and accurate phase distribution is presented. By intercepting a line on the same position from a
series of interferograms associating with the phase-shifter's characters and constructing the mathematic model for
intensity of the line on each interferogram, the correlative coefficients of the mode's function can be solved, one of
which is the wrapped phase. Then the voltage-unwrapped phase curve is obtained through unwrapping technique.
Results of computer simulation show a high accuracy after several fast iterations. In addition, taking an experiment for
example in our interferometer, the characteristic curve of phase shift over voltage change is presented in the end.
Experiment results show it can be an in-line calibration method for phase-shifer in PSI.
In this paper, a novel method named the virtual grating phase-shifting moire fringe method for static interferogram analysis is introduced in the straightness error measurement with optical interferometry. An optical flat as the test mirror is moved along the horizontal slideway with high accuracy in the experiment implemented on ZYGO. Based on the principle of small angle test, we measure the straightness error of the subsection guide in turn from the one end. Because of the slideway's straightness error, the optical flat couldn't keep moving along the optical axis. The variation of fringes tilt and fringes number can be seen from a series of static interferograms. Then each wavefront is retrieved by processing these interferograms with the virtual grating phase-shifting moire fringe method. With the theory of plane fitting algorithm, the angle between interference wavefront and optical axes is calculated from the angle between fitted plane and optical axes, then the guide track's departure from horizontal axes is obtained. The experiment results are presented at last.
A preliminary design study for a high-resolution echelle spectrograph to be used for LAMOST (The large Sky Area Multi-Object Fiber Spectroscopic Telescope) that is currently under construction is presented. In order to obtain a resolution-slit product of about 40000 as required by science case, the less expensive design used a 105mm beam feeding a 408mm deep Echelle is good solution.
The optical design of high resolution Echelle spectrograph for LAMOST is given. This spectrograph will be more powerful tool for astrophysical research using high-resolution spectroscopy in China. Some new technology and novel design concepts have been adopted in this spectrograph, such as white pupil collimator system, R4 Echelle with large blaze angle, and the fold and off-axial Schimidt camera without center obstruction and so on.