• Korean Journal of Optics and Photonics
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• v.13 no.2
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• pp.89-91
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• 2002

A test method that can measure the parallelism and the surface figure of an nontransparent plate using visible light is proposed. The testing system consists of a Twyman-Green interferometer. In addition, test results for the IR filter of IR MTF measuring system are described.

• Transactions of the Society of Information Storage Systems
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• v.4 no.1
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• pp.19-22
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• 2008

For the assembly and evaluation of solid immersion lens (SIL) optical head which is the key component of SIL based near field recording (NFR) technology, we modify the Twyman-Green interferometer. Super-hemisphere SIL optical head for the surface recording is assembled and evaluated by the modified Twyman-Green interferometer. In order to verify the optical performance of the assembled SIL optical head, we compare the measured results of the SIL optical head with the simulation ones. Finally, we show the feasibility of applying the assembled SIL optical head to near field recording system by the experiment of the dynamic gap control based on test bed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.269-273
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• 2004

The moduled interferometer with waveplates, polarizing beam splitter, etc. for four phase shifted interference patterns was stabilized with the and Fast Fourier Transform (FFT) method was used to investigate the surface profile measurement from the interferenece pattern from Twyman-Green interferometer using a mathcad.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.10
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• pp.203-208
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• 1999

By tilting the reference mirror of Twynman-Green interferometer having a reference mirror and a moving mirror, firinge pattern composed of bright and dark parallel lines can be obtained and the fringe pattern is shifted according to the displacement of the mowing mirror. Several studies are executed for displacement measurement by detecting the intensity of the fringe with photo-diodes having small detecting area. In this study, to improve the sensitivity and robustness, the intensity of fringe is detected by using a large-area quadratic photo-diode masked with a grating panel having four kinds of binary grating having phase-difference of 0, {\pi}$/4, {\pi}$/2, 3 {\pi}$/4. The phase of the fringe is calculated with a simple 4-buckets algorithm. A experimental result shows that standard deviation of 5.653 nm is obtained comparing with a capacitive type gap sensor having nearly 1 nm accuracy.

• Korean Journal of Optics and Photonics
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• v.2 no.4
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• pp.179-185
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• 1991

Twyman-Green interferometer is developed for assessment of IR optical system performance. Light source is $CO_2$ gas laser which has 10.6$\mu \textrm m$ wavelength. The light beam is expanded to 2.5 cm dia by Ge lens and splitted by ZnSe parallel plane plate. One of the beams is reflected by refernce mirror which is operated PZT. The fringe will be detected by a pyro-electric vidicon camera and displayed by a CRT monitor. Here, the IR firinge is recorded on the thermal paper. In visible region, the light source is He-Ne laser. The fringe is detected by a CCD camera and displayed by the CRT monitor. The intensity of the fringe is digitized by a image card and processed by a PC. The wavefront aberration function, PSF and OTF are calculated. The results are displayed in 3-D graphs on the monitor or printed out by a line printer.

• Korean Journal of Optics and Photonics
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• v.5 no.2
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• pp.191-197
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• 1994

We investigated the properties of various methods of 3 dimensional profilometry to choose the phase shifting technique for the reconstruction of the shape of a given specimen. The pattern was generated by a Twyman-Green interferometer and a PZT was used to shift the fringes on the target surface. The shape was calculated with Hariharan algorithm within the uncertainty of a scaling factor. The optical noise inherent in the laser source was observed to influence the final outcome to a great extent and the need for an exact calibration was noted. noted.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.199-203
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• 1997

Fine displacement of spherical suface was detected and analyzed by Twyman-Green interferometer and the interferogram analysis using Fourier transform method. The surface profile was obtained from single interferogram by introducing the carrier freguency to the interferogram. The interferogram was processed in the spatial frequency domain by fast Fourier transform, and the phase distribution was obtained by inverse Fourier transform. The 3-dimensional distribution for the surface displacement was obtained. It was compared with the calculated surface displacement and the error was less than λ/10.

• Korean Journal of Optics and Photonics
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• v.3 no.1
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• pp.20-26
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• 1992

The fourier transform method of retrieving the phase of the test wavefront from a Twyman-Green interferometer was reviewed by numerical simulations and experiments. Of the two methods reviewed, Takeda's approach proved more reliable in reconstructing the deformation of the test surface. The application of this approach to a plane mirror showed the existence of the surface curvature, whose maximum deviation was about $\lambda$/6. The accuracy in the measurement was evaluated to be around $\lambda$/40.

• Korean Journal of Optics and Photonics
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• v.11 no.2
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• pp.80-84
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• 2000

Parabolic almninium mlITOr of m.5('||'&'||'cent; 50 nun) was fabncated by a diamond tummg machine. Computer generated hologram (CGH) for the test of parabolic mirror was encoded by binary phase hologram Approximation of curved fringe to line was made by staircase encoding. After fringe data 1ransformed mto a Post Scnpt file. magnified master CGH was printed by a laser printer, and then it reduced to the photographIc film. Parabolic mirror was tested by Twyman-Green interferometer with CGH at VIewing arm. Its experimental result was compared with those of surface profile and auto-collimatIon test, and then the errors were analyzed.

• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.248-253
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• 2004

We propose a near- field scanning optical interferometer (NSOI) based on the facet reflection of a nano-sized moveable tapered optical fiber. The interferometer can measure the position and the wave-front of a focused spot simultaneously. The interfering fringes are generated by the reflected beams from the sample surface and from the fiber facet. The wave-front analysis at the focusing position is obtained by using a phase shifting technique with a four-step algorithm. It is found that the resolution for controlling the focal position of our proposed NSOI is less than λ/3 and the measured wave-front aberration at the focal position is in good agreement with the ones obtained by a Twyman-Green interferometer.