Automatic measurement of single points schema by coordinate measuring machine(CMM) is used to measure the Ultra-Long curvature radius of spherical optical element. The removal quantity of each measuring point can be calculated through contrasting the measure value and the theoretical value. A removal model of spherical optical element polishing is established based on Preston equation, and the required machining parameters are predicted by removal simulation in MATLAB. A processing test on a fused silicon with an aperture of 440mm×440mm was performed and the result shows that the model is effective in Ultra-Long curvature radius control of spherical optical element during full aperture polishing.
The large and thin plane optical windows are used in large high power laser devices. Typically conventional methods such as stressed-lap polishing and small-tool pitch polishing are used to manufacture these optics. Nevertheless, the required wavefront accuracy cannot be achieved by the last smal-tool pitch polishing process which can lead to middle spatial frequency errors and high-slope errors because of the edge effect , unstable removal rate and pressure -loaded deformation. Ion Beam Figuring (IBF) technology is an optical fabrication method which can highly correct different spatial frequency errors due to the highly deterministic, highly stable, very small tools and noncontact. In this paper, IBF was employed to correct different spatial frequency errors of a large and thin plane optical windows. Before IBF, transmission wavefront error of the substrate was 0.51λ PV, 32.3nm/cm GRMS, 2.91nm PSD1, 0.27nm PSD2, 0.38nm Rq after being polished by double-sided polishing machine, and was improved to 0.07λ PV, 2.1nm/cm GRMS, 1.76nm PSD1, 0.13nmPSD2, 0.33nmRq after only two IBF(about thirty six hours processing time). All spatial frequency errors reached the required values.
This article mainly take the research in controlling the parameters in the full aperture fine grinding and polishing stage of the 350mm×300mm×10mm size sapphire window. In the period of full aperture fine grinding period ,by adjusting the grinding parameters, the whole aperter parallel error of the sapphire window conversed to the level of below 3".In the period of full aperture polishing period , by adjusting the polishing parameters including the vaccum adsorbing parameterm, with those measures the wavefront error conversed to the PV value of 2λ(λ=632.8nm), the whole aperture parallel error of the sapphire window conversed to the level of below 3", and the inside arbitrary Φ100mm aperture’s parallel error also conversed to the level of below 3", the roughness of the polishing face attained to the value Rq≤2nm.Through the technical research in the full aperter processing of the sapphire window , the wavefront error, the parallel error and the surface roughness are well controlled which provide the fine results import in the fine sub-aperture polishing period.
Aiming at the improvement of edge effect in CNC polishing. A new polishing method based on the surface extension is proposed. The basic idea and workflow are presented. The availability of this method is verified by simulation. Experimental study was carried out on 420mm×420mm caliber fused quartz optical element. The experimental results show that this method can restrain the collapse and warped edge surface. PV less than λ/3,GRMS less than 7.7nm/cm and PSD1 less than 1.8nm can be obtained combining the small scale smoothing technology.
The in-situ monitoring of subsurface defects and laser damages initiation using high resolution on-line microscope is performed on medium aperture fused silica optics manufactured by different procedures to investigate the specific damage precursors. The digital camera, Nomarski microscope and white light interferometer are used to characterize the subsurface defects. With shallow HF etching depth, the laser induced damages are mostly initiated on indents or invisible defects under the fluence of 8~10 J/cm2@355nm. The laser induced damages initiated on indents is gradually decreased with the increased etching depth and the laser induced damage density is also decreased. Besides, decrease of the indents by optimizing the polishing process could also make the laser induced damage density sharply decrease. These results prove that the indents are important damage precursors and the laser induced damage performance of fused silica optics could be substantially improved by decreasing the indents or deep HF etching.
By the ion-beam figuring machine IBF600, a 630 mm aperture fused silica flat standard mirror was polished up to surface PV value 38.9 nm and RMS 6.556 nm in low frequency error, during the same time ,the mirror’s mid-spatial frequency(spatial frequency band 2.5 mm~33 mm) wavefront RMS error converged to 1.502 nm from initial value 2.022 nm.During the process, two removal functions were used in the simulation after parameter optimization. According to the residual error map, we choose the appropriate removal function and calculate the dwell time, finally we successfully attained the optical acquirements of the standard mirror in both low and middle frequency error, this high middle frequency.
This article mainly take the research on the technique of fabricating a steep off-axis aspherical mirror based on infrared interferometric testing. In the stage of asphercal shape grinding ,we take use of an infrared interferometer to test the aspherical surface error rapidly, along with the arm-swinging polishing method and choose the appropriate processing parameters according to the testing results. After more than twenty times polishing and testing circles ,the off-axis mirror’s wavefront error converge to PV≤5 λ,RMS≤1 λ(λ=632.8nm),this surface map is suitable for the final sub-surface polishing. Through these research and experiments, we have verified the applied advantage of infrared interferometric technique in fabricating steep off-axis aspherical mirror. This technology is also very useful in the processing other types of large-scale aspherical mirrors.
The ghost reflections can cause spurious fringes in the interferograms and lead to error in the measurement. So it is necessary to evaluate the influence of the ghost reflection spot for a correct interpretation of interferograms. In this paper, the ghost reflections of testing long focal length lens with computer-generated hologram (CGH) are investigated and geometrical model is established to obtain an expression for the size of the ghost reflection spot. Moreover, simulations and experiments are carried out by studying the ghost reflections of the long focal length lens in Shenguang III system.
The influence of polishing parameters such as particle size, pad material and pressure on the surface roughness of glass optics were investigated and analysed. It reveals that the surface roughness will get worse with increase of the polishing particle size. The surface roughness would remain stable in a certain period of polishing pressure, but get worse with increase of the pressure beyond the period. The surface roughness is getting better when using smooth pitch polishing pad than polyurethane pad with lots of micropores. By optimizing the polishing parameters, the surface roughness of large aperture fused silica window is improved to 0.46nm before band-pass filtering and 0.084nm after band-pass filtering.
In order to process full spatial frequency range error of steep aspheric surface, a self-adaption polishing tool was designed based on silly putty, and the principle of silly putty used on polishing tool to process middle and low spatial frequency errors was analyzed. The effect of silly putty’s viscosity on pressure was calculated by Newton’s law of viscosity. Stability of polishing pressure was compared between self-adaption polishing tool and pith lap through calculating polishing pressure. A 470mm aperture concave aspheric whit F#1.8 and 1.8mm departure from the best-fit radius is employed to operate experiment. It was verified that self-adaption polishing tool have the capability processing full frequency range error.
The effect of ion beam etching process on the surface quality, the surface roughness and the laser-induced damage threshold at 351nm was carried out. Research results reveal that the laser-induced damage threshold of fused silica was enhanced with the increase of etching depth when the etching depth was less than 800nm, and could be further enhanced about 30% at 800nm etching depth, however the laser-induced damage threshold began to decrease with the further increase of etching depth(more than 800nm). The test results of surface microtopography, laser damage morphology, and surface roughness reveal that the ion beam etching process can remove polishing re-deposition layer without degrading the surface condition at a smaller etching depth so as to enhance the laser-induced damage threshold of fused silica, however further ion etching which can produce impurity particle often results in a decrease rather than an increase of laser-induced damage threshold.
A method for measuring the wavefront of wedged focus lens by using the Fizeau interferometer with large aperture and a reflective computer generated hologram (CGH) is proposed. The CGH has 6 zones: one main zone for the null testing of wedged focus lens, one additional zone for alignment the CGH substrate with the interferometer, and four others for the pre-alignment of wedged focus lens by projecting four marks. CGH design process was performed, including the ray trace model for multizone CGH and the optical testing configuration. Simulation results show that the desired precision can be reached with use of CGH and confirm the feasibility of this measurement method.
Light weighted multi-angle multi-surface mirror is made of glass-ceramic, with the structural characteristic of multicavity thin wall, high precision of surface figure and angle between surfaces, has very different processing technology with traditional solid mirror. Based on the 460mm×434mm×80mm multi-angle multi-surface mirror, glass combination manufacture method and relevant interferometry of angle measurement was designed. The process technology was studied, then the consistency of angle between surfaces and the influence on multi-cavity thin wall deformation of lateral surface and material of polishing pad on the surface figure processing were controlled. The model between the variation of angle and load was established, from which the hysteresis of angle variation was analyzed, then the prototype workpiece was finished. The difficult problem on synchronically controlling the surface angles and surface figure of the mirror, which has high center of gravity and multi-cavity thin wall, was solved. The lateral surface figure was controlled below λ/6 (PV, λ=632.8nm), and the perpendicularity of lateral surfaces were controlled below 5''.
A 520mm aperture SiC flat mirror was manufactured up to RMS accuracy of 10.8nm in 50 days. Through the analysis of SiC material removal principle during full aperture polishing, we chose the appropriate parameters of polishing in full aperture polishing process and quickly made the surface error convergence to RMS value 100nm, then we took the step to small tool polishing, the adjustment of the remove function in this process was taken in order to coordinate the hard material’s properties, the efficiency in PV and RMS convergence was presented according to the experimental results. After four week’s polishing ,the RMS value successfully reduced to 10.8 nm and reached the technical requirements of this large flat SiC mirror.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.