The response characteristics of the pitch polishing pad under the pressure of conditioner is the key factor which affect the control efficacy of surface figure in annular polishing. The effect of the environmental temperature and humidity, rotation speed of the pad, uploading ratio and eccentricity of the conditioner on the response characteristics of pitch polishing pad were experimental researched. To this aim, a control system of the environmental temperature and humidity on the 2.8m-aperture annular polishing machine is established. The control precision of the local environmental temperature upon the pad is up to ±0.1℃, and the control precision of humidity is up to ±1% RH. The experimental results indicate that the matching degree of the pad and the conditioner decides the changing rule of the surface figure of workpiece with the eccentricity of the conditioner. The new adjustable parameters including the environmental temperature and humidity and the uploading ratio of the conditioner were introduced to change the matching degree and improve the controllability of the of the surface figure. Under the optimized process, the long-term stability of the surface figure of the meter-scale optical element is realized using the 2.8m annular polishing machine, which is an important step for the final realization of the deterministic processing in the large-aperture annular polishing.
KEYWORDS: High power lasers, Geometrical optics, Lithium, Image analysis, Ions, Roads, Laser damage threshold, Optical components, Diffraction, Control systems
In high power laser facilities, the ghost images was usually considered for the spot position and energy
density with geometrical optics (GO) but couldn't obtained the ghost images focal spot which was also essential for the
ghost images damage threshold. And the energy redistribution on focal spots may induce undesired partial damage as
well. Therefore, Collins formula was applying on a single lens to analyze the ghost images focal spot detailed
distribution in space. The results were consistent with GO and the output spots on focus were same to Airy spot with
different size in different reflection orders.
In high power laser systems, the high-frequency noise generated by nonlinear effect is effectively removed by
low-pass spatial filter, and the low-frequency noise passing through pinhole is always considered as very safe
to optical devices in downstream. However, in practical applications both modulation contrast ratio and
spatial frequency of the low-frequency noise will be changed and possibly become dangerous components,
depending on different magnification ratios of spatial filter. In this paper, the evolution of low-frequency
noise is theoretically analyzed and numerical simulated depending on different magnification ratios of spatial
filter. The analysis results show that both modulation contrast ratio and spatial frequency of the
low-frequency noise passing through pinhole will be changed 1/M times, where M is magnification ratio of
spatial filter. For M<1, the safe low-frequency noise will be extruded into high-frequency which is the fastest
growing components and finally develop into the most dangerous part to the damage of optical devices again.
It is significant to consider the evolution of low-frequency noise in practical applications of spatial filter for
high power laser system.
A phase retrieval algorithm which only needs to measure the intensity distribution at two positions was used
to reconstruct laser wavefront. It was further applied in high power laser. Results were obtained from the phase retrieval algorithm in the visible band, and the effects of measurement error on the phase retrieval process have been simulated. This algorithm is not sensitive to measurement error, but sensitive to the relative distribution of light intensity.
This paper presents a new method for measuring vibration based on interference from two spherical waves. By
integrating the two interference arms into a beamsplitter cube by reflective film and the probe beam being divided into
two parts, the interferometer can distinguish that the vibrations are from the monitored optical components or from laser
interferometer system itself. At the same time, because the two interference waves are spherical, it can realize monitoring
the three-dimensional vibrations. The experimental setup has advantages of being stable and reliable with an integrated
structure. Theoretical analysis and experimental demonstration are performed. The experiment results indicate that the
method can monitor three-dimensional vibration sensitively.
Nowadays, GaN-based multi-layer materials is developing fast, and it is important to know their
interface and optical properties for devices design and fabrication. In this letter, the transmission
spectra are analyzed, and the dependence of the transmission spectra on parameters of the samples is
discussed. Sequentially, we obtain the transmission spectra of a series of GaN-based samples.
Simulation of the transmission spectra is done and useful information is extracted. For one of our
samples, the refractive index varies a little between 2.518 and 2.305 with the wavelength from 400 to
800nm, while the extinction coefficient is 6x-10-9.5exp(2700/λ), and the thickness is 2860nm. Finally,
we get the dispersion relationship of the GaN and AlGaN films, and it is compared with the results of
some other research groups.
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