• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.643-648
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• 2003

The phase-shifting diffraction-grating interferometer proposed in the investigation uses a diffraction grating that performs manifold functions of beam splitting, beam recombination, and phase shifting. The reference and measurement waves generated by means of diffraction have different amplitudes depending on their orders of diffraction, so the interference fringe pattern resulting from the two waves tends to yield poor visibility. To cope with this problem, we select a phase grating of reflection type and attempt to improve the interference visibility with optimization of the groove shape of the grating through electromagnetic analysis.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.39-45
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• 2004

A computer simulation about removal of the 0-th order diffraction is achieved by using numerical reconstruction in digital holography and the Fourier transform method. A light intensity distribution hologram is generated through numerical calculation of the interference pattern. Additionally a phase hologram without the 0-th order diffraction is generated. The removal function for elimination of the 0-the order diffraction is introduced and the numerical reconstructions with several conditions for the removal of the 0-th order diffraction and the production of high quality numerically reconstructed images are tested and compared. The removal function is proven to be more effective at the suppression of the 0-th order diffraction compared with the DC suppression method.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.323-328
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• 2006

A fundamental problem in digital holography is the presence of zero-order noise in the reconstruction process, which decreases the signal to noise ratio(SNR). For many applications, that reduction of SNR makes digital holography impractical, so a great number of approaches have been tested in order to overcome such a problem. In this paper we use the scanning method to suppress the zero-order diffraction noise and the interference noise between object beams. We demonstrate that it is possible to increase the image quality with the scanning method.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.148-149
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• 2003

렌즈와 거울의 형상을 정밀하게 측정하고 평가하는 광학시험에 많은 형태의 광간섭계가 개발되고 사용되어왔다. 그 중, 회절격자를 광선분할기로 사용하는 광간섭계들을 통칭하여 회절격자 간섭계라 부른다. 회절격자 간섭계는 별개의 광학표면을 사용하지 않고 회절격자에서 회절된 파면을 직접 기준파면으로 사용할 수 있으므로, 격자의 형태, 주기를 선정하여 기준파면과 측정파면을 원하는 방향으로 재생하여 다양한 형태의 간섭계를 만들 수 있다.(중략)

• Korean Journal of Optics and Photonics
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• v.12 no.6
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• pp.496-502
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• 2001

We generated a nondiffracting beam and investigated its intensity profile on propagation. We first obtained an annular output beam from Nd:YAG laser with a negative branch unstable ring resonator and, using a 1m focal length lens, we generated a Bessel- Gauss beam. The inner radius of the annular output beam was 2.57 mm and the ring width was 0.145 mm. The intensity profile of the nondiffracting beam did not show any appreciable diffraction up to 33 m distance from the focal lens. This result was compared with the theory.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.50-51
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• 2000

가속된 전자빔을 금속회절격자의 위로 통과시킬 때 결맞은 복사광(coherent radiation)이 발생하는데 이를 Smith- Purcell 효과라고 한다. 이때 발생하는 전자기파의 파장은 회절격자의 주기, 전자빔의 속도 및 복사광의 방출각도에 관계된다$^{(1)}$ . 그리고 방출된 복사광의 출력세기는 전자빔의 군집을 고려하지 않는 경우, 회절이론(diffraction theory)에 의해 얻을 수 있는데, 그 세기는 입사시킨 전자빔의 전류세기에 선형적으로 비례한다$^{(2)}$ . (중략)

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.434-439
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• 1996

To investigate influence of the incident beams which have the truncated Gaussian amplitude and of the shapes of bump on read-out signal is an optical disc, and the point spread function on bump, the scalar diffraction theory is used in this paper. We consider the truncated Gaussian amplitudes which are $\sigma$=0, 0.5, 1.5, and 2.5, the height of bump which is given by $n{\Delta}_0={\lambda}/4$, and the phase height of bump which is then given by ${\Phi}_0={\pi}$. We also consider the shapes of the bump which are a rectangular shape, a frustoconical shape, and a conical shape. It is shown that as the truncation of incident beam reduces the radius of central spot on bump decreases, the maximum value of read-out signal increases, and that the size of bump decreases. From these results, we get better read-out signal and the reduced cross-talk in optical disc when the truncation of incident beam reduces. Therefore a laser beam having less truncated Gaussian amplitude may useful for an actual optical disc.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.7
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• pp.36-42
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• 2000

Some polarization characteristics of reflection type photopolymer are investigated. Photopolymer on a Mylar substrate alters an incoming linearly polarized laser beam to an elliptical polarization. Due to the rotation of the polarization, the recording gratings show different diffraction efficiencies. The rotation angle is of order of 10-50% for the tested samples. It is found that the polymer layer does not changes the polarization direction but the Mylar substrate alone distorts the incoming polarization to a comparable degree. As align the polarization states of photopolymers to be parallel with a laser using a He-Ne laser(633nm), which is not sensitive to that material, it was possible to make high diffraction efficiency gratings.

• Korean Journal of Optics and Photonics
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• v.15 no.1
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• pp.56-62
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• 2004

We present a diffraction grating interferometer of large equivalent wavelength specially designed for flatness testing of rough surfaces. Two transmission diffraction gratings are illuminated on the object under test by use of two measurement beams with different angles of incidence, which yields a large equivalent wavelength. This interferometer design minimizes unnecessary diffraction rays and the systematic error caused by the diffraction gratings, and provides a large working distance and easy alignment. To improve the measurement accuracy, phase shifting technique is applied and the equivalent wavelength error caused by defocus is calibrated. Test results obtained from mirror surfaces and machined rough surfaces are discussed.

• Optical Science and Technology
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• v.8 no.2
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• pp.22-26
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• 2004

회절 광학 소자(Diffractive optical element)는 광학 시스템에 있어서 광을 조절하기 위하여 굴절(refraction) 또는 반사(reflection)보다는 주기 구조(periodic structures)에 의한 회절(diffraction)을 이용한 소자라 할 수 있다. DOE의 장점으로는 수차(aberration)가 없는 point-to-point 이미지가 가능하며 광 power를 사용한 평판(flat subface)이 가능하고 비구면과 같은 수차 조절이 가능하다. 단점으로는 HOE(Hologram Optical Element: DOE의 일종)의 수차가 이 구조의 특정 파장에서 나타나고 가시영역의 일정 영역에서 매우 분산적 (dispersive)이다. 또한 상대적으로 시장의 성장에 비하여 찾는 고객의 수가 적다는 점이다.(중략)