Shibin Wu

Measurement of an off-axis parabolic mirror using coordinates measurement machine and swing arm profilometer during the grinding process

We present the measurement methods for off-axis parabolic mirrors using Coordinates Measurement Machine and Swing Arm Profilometer during the grinding process. An off-axis parabolic mirror with 1200mm in parent focal length, 360mm in off-axis displacement and 410mm in diameter is measured using the methods introduced in this paper. The convergence curves of the surface error are reported, which is reduced from 204.7μm in PV, 55.3μm in rms to 1.1μm in PV, 0.3μm in rms after 39 iterations of grinding. Besides, the measurement methods are able to control the parent focal length and off-axis displacement to less than 0.1mm tolerance. An interferometric result is presented, which validates the measurement methods.

Error separation technique for measuring aspheric surface based on dual probes

In this paper, we present an error separation method based on dual probes for the swing arm profilometer to calibrate the rotary table errors. Two probes and the rotation axis of swinging arm are in a plane. The scanning tracks cross each other as both probes scan the mirror edge to edge. Since the surface heights should ideally be the same at these scanning crossings, this crossings height information can be used to calibrate the rotary table errors. But the crossings height information contains the swing arm air bearing errors and measurement errors of probes. The errors seriously affect the correction accuracy of rotary table errors. The swing arm air bearing errors and measurement errors of probes are randomly distributed, we use least square method to remove these errors. In this paper, we present the geometry of the dual probe swing arm profilometer system, and the profiling pattern made by both probes. We analyze the influence the probe separation has on the measurement results. The algorithm for stitching together the scans into a surface is also presented. The difference of the surface heights at the crossings of the adjacent scans is used to find a transformation that describes the rotary table errors and then to correct for the errors. To prove the error separation method based on a dual probe can successfully calibrate the rotary table errors, we establish SAP error model and simulate the effect of the error separation method based on a dual probe on calibrating the rotary table errors.

Design and development of 24 times high-power laser beam expander

As currently, laser calibration, laser radar, laser ranging and the relative field raised up the demand for high magnification laser beam expander. This article intends to introduce a high-energy laser beam expander research and design, large- diameter, wide-band, high-magnification and small obscuration ratio are the main features. By using Cassegrain reflective optical system, this laser beam expander achieves 24 times beam expand, and outgoing effective limiting aperture is Φ600 mm, band scope between 0.45μm to 5μm, single-pulse laser damage threshold greater than 1J/cm2, continuous-wave laser damage threshold greater than 200W/cm2 and obscuration ratio 1:10. Primary mirror underside support uses 9 points float supporting, lateral support mainly depends on mercury belt support and assists by mandrel ball head positioning support. An analyzing base on finite element analysis software ANSYS, and primary mirror deformation status analysis with debug mode and operativemode, when inputs four groups of Angle 170°, 180°, 210° and 240° , mercury belt under each group of angle load-bearing is 65%, 75% , 85% and 100% respectively, totally 16 workingcondition analyze results. At last, the best way to support primary mirror is finalized. Through design of secondary mirror to achieve a five-dimensional precision fine-tune. By assembling and debugging laser beam expander, Zygo interferometer detection system proof image quality (RMS) is 0.043λ (λ=632.8nm), stability (RMS) is 0.007λ (λ=632.8nm), and effective transmission hit 94%, meets the requirements of practical application completely.

Optimization design and error analysis of moiré deflection system

Moiré deflectometry is used for the measurement of focal lengths of optical lenses in this paper. Detailed uncertainty analysis is done, and achievable accuracy is discussed. To increase the measurement accuracy, we propose two useful ways by changing the two systemic parameters (angle and space between two gratings). Firstly, we find that the space between two gratings affect the error from the tilt angle of moiré fringe greatly. And optimum space between two gratings for minimum error is referred to. In the other hand, enhancing the angle between the two gratings rulings lines moderately can reduce error from the angle of two gratings greatly. Theoretical analysis and experimental results indicate that, higher measurement accuracy can be achieved by changing the systemic parameters opportunely.

Quantitative measurement of optical surfaces using an improved knife edge

One of the oldest techniques for sensing optical abberations is Foucault knife edge test. Qualitative properties of knife edge test have been utilized over the past 150 years to assess the quality of an optic or optical system. Much work and analysis have been performed since Foucault,but no satisfactory results have been found. This paper describes a method that upgrades the knife edge tester from a qualitative tester to a quantitative tester.Firstly,the traditional knife edge tester is upgraded to an improved one enabling the knife to cut the focus from horizontal direction and vertical direction.Secondly,the 2 sets of shadows were integrated to form complete mirror shadows.Finally,a mathematical model is established to quantitatively evaluate the surface error from the shadows. An experiment has been done using the method. The calculated deviations of the optical surface are compared with the results measured by ZYGO interferometer. Two measurement results show resemblance.

Development of a parallelism tester for visible and infrared compound system

A parallelism tester is developed to measure the parallelism of the visible optical axis and infrared optical axis of visible and infrared compound system.The tester is composed of visible system, infrared system, cassegrain autocollimator, imaging and data processing system and 5D workshop. The visible system generates visible light. The infrared system generates the infrared light. The visible light and infrared light are auto-collimated by the Cassegrain auto-collimator. During measurement the autocollimated light is directed into the optical path of the compound system being tested ,which passes through the compound system being tested and back to the tester. The visible light is used for targetting and infrared light is used for measurement. An 5D workshop is used for adjustment. The imaging and data processing system detects the deviation of infrared light spots and calculate the parallelism of the visible optical axis and infrared optical axis of visible and infrared compound system.The tester can be used to measure the parallelism of visible optical axis and infrared optical axis of visible and infrared compound system. The calibrated accuracy of the tester is 3 arc second.

Research on the measurement of large glass stress distribution

A primary mirror is the key component for telescope. For getting high-quality primary mirror the most important work is to measure and control glass stress distribution. At present small size glass can be accurately measured, but how to measure large mirrors has not been broken though. For developing measurement technology, a new method by making use of reflected mirror to extract polarized beam is brought forward to measure large glass. At first, theory analysis has been done that is about the interaction between polarized beam and reflected mirrors. Then experimental measurement has been carried out by use of the method. A conclusion which can be drawn out is that by controlling the refractive index and thickness of reflected coating, polarization state of reflected beam can be kept in the same state to the incident beam when the polarized beam passes through the reflected mirrors.

Development of Bubble Tester

A Bubble Tester is developed to do the measurements of bubble classes for optical elements. The tester is composed of illumination system,refractor slot, imaging system,CCD,computer controller and data processor,3D workshop and ground base. The light from the illumination system is refracted by the bubbles and inclosures in the optical elements, the imaging system captured the light and imaged the image to CCD and computer captured the image and did data processing to get the dimension, quantity and distribution of the bubbles and enclosures. The tester can measure bubbles with Φ0.05~Φ5mm in diameter and the accuracy is 5%.The tester can measure bubbles and enclosures of optical elements and welding line of the optics according to GB 7661-87.

Measurement of optical surfaces with knife edge method

A method that upgrades the knife edge tester from a qualitative tester to a quantitative one was introduced in this paper. Moving the knife edge tester back and forth in the focus of the mirror, the variations at the center of curverture of annuluses of the mirror can be got. Using mathematic method, these variations of the center of curverture can be calculated as the deviations of real surface to perfect surface. An experiment has been done by using the method. The calculated deviations of the optical surface was compared with the results measured by Form Talysurf PGI 1240 from Taylor Hobson. Two-measurement results show resemblance.

Current development of advanced optical technology in IOE, CAS

Current development of advanced optical technology in Institute of Optics and Electronics, Chinese Academy of Sciences is reported in this presentation. In advanced optical manufacturing technologies, the large astronomical telescopes, the large mirrors and the light-weighted mirrors are being developed in our Institute. The active manufacture technology of the large mirror is being carried on. In advanced optical testing technologies, we have developed a serial of Hartmann-Shack wavefront sensors used in this field. Furthermore, Adaptive optical technology has been developed and successfully applied in astronomical observation, ICF facility and high resolution retinal imaging of human eye in IOE, CAS.