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최희주,변혜현,임환홍,차명식 한국물리학회 2010 새물리 Vol.60 No.4
We applied three different optical methods to check the parallelism between the two surfaces of a transparent substrate. The first method is based on geometrical optics. A laser beam is incident on the substrate, and the deviation of the reflected beams, caused by the wedge, is measured. In the second method, a laser beam is focused to the sample, producing an interference pattern between the two reflected divergent light waves. The center of the fringe pattern rotates with the sample rotation if any non-zero wedge angle is present. In the last method, we observe the Fizeau fringes or the Haidinger fringes from the reflection of an extended monochromatic source. Comparing the three methods, we conclude that the last method provides a quick, simple and accurate estimation of the wedge angle of a transparent substrate. 우리는 기판형태의 투명한 광학매질의 양면 평행도를 세 가지 광학적 실험 방법을 통해 평가해보았다. 첫 번째 방법은 기학광학을 이용한 방법으로 비스듬히 시료에 입사한 빔이 시료의 앞, 뒷면에 의해 반사되어 나온 두 빔 사이의 거리를 측정하여 기울어진 각도를 측정하는 것이며, 두번째 방법으로는 시료 근처에서 초점을 맺는 광원을 이용하여, 시료 양면에서 반사된 발사하는 두 빛의 간섭무늬를 이용하는 것이다. 만약 시료의 양면이 기울어져 있다면, 시료를 회전시킴에 따라 간섭무늬의 중심도 회전하고, 이때 회전하는 원의 반경을 측정하여 기울어진 각도를 알 수 있었다. 마지막 방법은 단색광을 이용하여 시료로부터 만들어지는 하이딩거 무늬와 피조 무늬를 관측하는 것이다. 우리는 기판형태의 투명한 광학매질의 평행도를 평가하는 방법으로 위 세 가지 방법 중 마지막 방법이 가장 간편하며, 넓은 시료에 대해 정확하고 빠른 평가를 내릴 수 있는 것으로 결론지었다.
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Measurement of the Birefringence in Bulk Optical Media by Using Interferometric Methods
차명식,최희주,임환홍,김병주 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6
Accurate knowledge of the index of refraction of an optical medium is of fundamental impor- tance in various optical applications. We applied a Michelson interferometer and Fabry-Perot-type interference methods to a wafer sample to estimate the difference between two orthogonal indices, Δn, of a LiNbO3 crystal wafer and we compared the results of the two methods. By measuring the transmittance with sample rotation, we obtained a beat pattern between the fringes of the ordinary and the extraordinary light waves. Fitting the node locations, we could determine the Δn value with an uncertainty of 10-3 with both methods. Since the Fabry-Perot method is insensitive to atmospheric turbulence and vibration and is very simple to implement, it alow a quick estimate of the birefringence in optical crystals.
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Photoluminescence and Lasing Properties of ZnO Nanorods
이건준,이영백,임환홍,차명식,Sung Soo Kim,정현식,민선기,한성환 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.61
In this study, we investigated the structures, photoluminescence (PL), and lasing characteristics of the ZnO nanorods prepared by using chemical bath deposition. The continuous-wave HeCd laserexcited PL spectra of the ZnO nanorods exhibited two emission bands, one in the UV region and the other in the visible region. The UV emission band has its peak at 3.25 eV with a bandwidth of 160 meV. However, the PL spectra under 355-nm, 35-ps pulse excitation exhibited a spectrally-narrowed UV emission band with a peak at 3.20 eV and a spectral width of 35 meV. The lasing phenomena were ascribed to the amplified spontaneous emission (ASE) caused by coupling of the microcavity effect of ZnO nanorods and the high-intensity excitation. Above the lasing threshold, the ASE peak intensity exhibited a superlinear dependence on the excitation intensity. For an excitation pulse energy of 3 mJ, the ASE peak intensity was increased by enlarging the length of the ZnO nanorods from 1 µm to 4 µm. In addition, the PL spectrum under 800-nm femtosecond pulse excitation exhibited second harmonic generation, as well as the multiphoton absorption-induced UV emission band. In this research, ZnO nanorods were grown on seed layers by using chemical bath deposition in an aqueous solution of Zn(NO3)2 and hexamethyltetramine. The seed layers were prepared on conducting glass substrates by dip coating in an aqueous colloidal dispersion containing 50% 70-nm ZnO nanoparticles. Scanning electron microscopy clearly revealed that ZnO nanorods were successfully grown on the seed layers.
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Demonstration of a Standing Light Wave with a Laser Pointer
김민성,김병주,Krishnamoorthy Pandiyan,임환홍,차명식 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.5
Wiener’s historic experiment on a standing light wave in 1890 introduced a representative example of the electromagnetic field superposition of light in modern textbooks on optics. In this research, we simply reproduce the experiment of Wiener for classroom demonstration. By using an inexpensive laser pointer as a light source and a weak diffuse reflection from slightly surface-scratched glass instead of photographic plates or fluorescent films, we demonstrate a standing light wave in real time. Furthermore, the coherence of the laser pointer can also be investigated in a simple experimental setup.
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Michelson 간섭계를 이용한 유리 및 결정 매질의 굴절률 측정
최희주,차명식,김병주,임환홍 한국물리학회 2006 새물리 Vol.53 No.6
We measured the refractive indices of fused silica and LiNbO$_3$ single crystal plates by using Michelson interferometer. Although the conventional fringe-counting method can provide index values with relative ease, it generates large errors. We employed an improved fringe analysis method and, as a result, obtained a refractive index value of 1.457 for the fused silica substrate and an the ordinary index value of 2.286 for the LiNbO$_3$ crystal, with an uncertainty in of 10$^{-3}$ or below. This method can be utilized in establishing accurate Sellmeier's equations for solid optical media. 마이켈슨 (Michelson) 간섭계를 이용하여 용융석영유리와 LiNbO$_3$ 단결정 평판형 시료의 굴절률을 측정하였다. 이 방법을 사용하면 고체 매질의 굴절률을 비교적 손쉽게 측정할 수 있으나, 일반적으로 간섭무늬의 개수를 세는 방법은 매우 큰 오차를 보이므로 우리는 Michelson 간섭계를 이용하되 굴절률 측정의 정확도를 높일 수 있는 방법을 모색해보았다. 개량된 방법으로 용융석영유리의 굴절률은 1.457, LiNbO$_3$ 결정의 정상광 굴절률은 2.286로 측정하여 굴절률 측정값의 불확실성을 10$^{-3}$ 이하로 줄일 수 있었다. 이 방법은 고체 광학 매질의 굴절률 분산식 수립에 쉽게 적용될 수 있을 것으로 기대된다.
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Jae Hyun Park,차명식,임환홍,전옥엽,박상혁,박수영 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
A strong blue (460 nm) upconverted fluorescence was observed in an organic single crystal composed of excited-state intramolecular proton transfer molecules with pumping wavelength range from 485 to 687 nm. We deduced the two-photon absorption (TPA) spectrum by measuring the upconverted fluorescence with varying pump wavelength. The TPA spectrum reflected the major features of the molecular one-photon absorption spectrum, but the overall two-photon absorption coefficient decreased with pump wavelength.
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