This article describes the method of mathematically stitching together a plurality of overlapping individual annular sub-aperture maps to yield the full-aperture map of an asphero-diffractive surface. The unknown step height and relative position of each zone causes some ambiguity when the individual sub-apertures are combined into a full aperture map. The uncertainty is mainly caused by alignment error and noise during the measurements of individual sub-aperture maps and step height. The optimization and merit function works to minimize the discrepancy between multiple data sets by including components related to various alignment errors and noise during the measurements of individual sub-aperture maps and step height. The stitching coefficients which minimize the mean square difference between any overlapping values can be found through iterative constrained optimization. The full aperture wave-front is reconstructed by stitching sub-apertures with the stitching coefficients within meaningful bounds.
Significant errors could be result from multiple data sets due to error transfer and accumulation in each sub-aperture. The constrained simultaneous stitching method with error calibration is proposed to increase the stability of the numerical solution of the stitching algorithm. Global averaging error and constrained optimization are applied to simultaneous stitching after alignment errors calibrated. The goal of optimization and merit function is the minimization of the discrepancy between multiple data sets by including components related to various alignment errors. The values for stitching coefficients that fall within the unit sphere and minimize the mean square difference between and overlapping values can be found by iterative constrained optimization. At last, the full aperture wave-front was reconstructed by simultaneous stitching with the stitching coefficients required to remain within meaningful bounds.
The effects of photostability on the ration of signal to noise in degenerate four-wave mixing (DFWM) using
backward geometry have been first investigated in iodine vapor. Frequency-doubled outputs from a
multi-mode Nd:YAG laser pumped dye laser, which laser dye PM580 was dissolved in the ethanol. Though
phase-match is automatically achieved in the backward folded boxcars geometry, weak signal beams under
the strong background of stray light are hardly detected because of the photostability on the ratio of signal
to noise in DFWM experiments. To solve the problems, a new image processing system for detecting
backward DFWM spectroscopy on iodine vapor is reported. This system is composed of CCD camera,
imaging processing card and the related software. With the help of the detecting system, the focal image
and the beam image of the pump laser's conjugation beam in backward geometry DFWM experiment have
been obtain, in which demonstrated that the backward geometry can't compensate the beam excursion. The
DFWM signal is sensitive to disturb of the environment, which leads to the phase conjugation fidelity
decreased. The study of photostability on the ratio of signal to noise in DFWM experiment is of importance
to trace atom, molecular and radical in combustion diagnosis.
We present a novel strategies and a prototype for large optical surfaces test with subaperture stitching. The kinematics
model with six degrees of freedom is built to determine the initial configuration of each subaperture, according to the
records of nulling motion. An alignment error model based on wavefront aberrations is established for compensation and
error separation. Subapertures are primarily stitched by homogeneous coordinate transformation, least square method
and Zernike polynomial fitting. Then an error-separation matrix of stitching model is developed to analysis the
characteristics and effects of alignment error on test results. The expressions of the alignment errors for aspheric surface
testing are built based on motion structure and wavefront aberrations theory. So the alignment errors can be separated
and compensated efficiently. Subapertures are then simultaneously stitched by minimizing deviations among the
overlapping region, as well as deviations from the nominal surface. As a result, precise prior knowledge of the nulling
and alignment motion, which is of six degrees of freedom, is no longer required. Simulations and experiments are given
to verify the validity and precision of the proposed algorithm. The result shows that the proposed method with alignment
compensation is quite efficient.
Degenerate four-wave mixing (DFWM) is a parametric process constrained by conversation of momentum of
the incident and reflected photons, which imposes the condition of phase matching on the incident and generated
signal beams. However, phase-match is not automatically achieved in the forward folded boxcars geometry. Also,
weak signal beams under the strong background of stray light are hardly positioned and distinguished. To solve the
problems, a new image processing system for detecting forward DFWM spectroscopy on iodine vapor is reported.
This system is composed of CCD camera, imaging processing card and the related software. With the help of the
detecting system, phase matching can be easily achieved in the optical arrangement by crossing the two pumps and
the probe as diagonals linking opposite corners of a rectangular box. The signal is generated in the center of the
box and propagates along the fourth diagonal, thus providing good spatial separation from the intense pump beams
and providing a way to position the PhotoMultiplier Tube (PMT). Also it is practical to know the effect of the
pointing stability on the optical path by monitoring facula changing with the laser beam pointing and disturbs of
the environment. Finally Real-time detecting the rate of signal to noise so as to timely decrease the stray light with
correct methods. Steady DFWM signals have been obtained in the experiment. This system makes it feasible that
the potential application of FG-DFWM is used as a diagnostic tool in combustion research and environment