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Amplified total internal reflection from a plane dielectric boundary
제원호,Jaewoo Noh,Hyoung Joo Kim,Wonho Jhe 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.1
We studied the amplification of a light beam that undergoes a total internal re ection at a plane dielectric boundary where only the lower index medium has gain. Experimental results indicate that the amplied total internal re ection is caused by stimulated emission of evanescent photons through interactions of dye molecules with the evanescent wave in the lower index medium. The amplication gain has sharp angular dependence and a linear power dependence.
Time-symmetry Breaking in a Modulated Cold Atom System: An Ideal Mean-field Transition
허명선,제원호 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.4
We realize an ideal mean-field transition of time-translation symmetry in a periodically-driven atomic system. The symmetry in steady-state oscillatory atomic motions spontaneously changes with the total number of atoms due to the interplay between inter-atomic interactions which originate from the attenuation effects in the trapping laser light and thermal fluctuations. A large separation of the time scales governing the transition suppresses the spatial dependence of the system dynamics, leading to a mean-field behavior even close to the transition point.
문걸,제원호,노흥렬 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.5
We report an analytical study of a Duffing oscillator realized in an intensity-modulated magnetooptical trap of ^(85)Rb atoms under the σ^+ − σ^- polarization configuration of lasers. The hysteresis curve of the atomic vibrational amplitude was calculated analytically using a simple transition line F_g = 0 → F_e = 1 instead of a real atomic transition line for ^(85)Rb atoms. The dependence of the nonlinearity on various parameters, such as the saturation parameter, laser detuning, magnetic field gradient, and modulation amplitude, were investigated through the parameter space domain. The characteristics of nonlinearity in this system could be understood clearly and simply in terms of the analytical results.
노흥렬,김기환,제원호 한국물리학회 2006 새물리 Vol.52 No.2
자기광학 포획에서 포획상수를 측정해서 3차원 구조의 다준위 원자에 대한 도플러 냉각 이론을 연구하였다. 포획된 원자에 일정한 자기장을 인가한 다음 자기장이 사라지는 과정에서의 원자의 궤적을 측정해서 감쇠계수와 용수철 상수를 구하였다. 종방향 축과 수직축 방향의 레이저 변수에 의한 포획상수의 변화를 조사해서 비율방정식을 이용한 계산결과와 잘 일치함을 확인하였다. 또한 넓은 레이저 변수 범위에서 평균된 포화세기를 사용하면 근사적으로 포획상수를 기술할 수 있음을 보였다. 특히, 감쇠계수의 결과에서 초도플러 힘이 중요한 역할을 수행함을 확인하였으며 감쇠계수에서 공명 현상을 관측하였다. The Doppler cooling theory for multilevel atoms in a three-dimensional magneto-optical trap was studied by measuring the trap parameters. After the constant magnetic field applied to the trapped atoms had been switched off, the damping coefficients and the spring constants were measured by recording the atomic trajectories. We found that the measured trap parameters depending on the experimental parameters of the longitudinal and the transverse lasers and were in good agreements with the calculated results based on a rate equation model. Also, it was found that the trap parameters of a simple two-level model could be used in terms of the averaged saturation parameter over a broad range of experimental conditions. In particular, we found that the existence of a sub-Doppler trap played an important role in analyzing the damping coefficients and in observing resonance-like phenomena in the damping coefficients.
Fano-type Transmission in Carbon Nanotube Array with Al2O3
Hojin Cho,제원호,정현영,서정쌍,박규환 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.1
Fano-type transmission, of which the specifics lie in continuum and resonant transmission, has been exploited in various areas since Fano published his study [1]. In this paper, we show macroscopic transmission fitted well with Fano analysis, using a sample composed of Al2O3 and multi-wall carbon nanotube. In addition to fitting, the properties of Fano-type transmission were shown to be its resonance and the interference of continuum and resonant transmission, of which the quantity was also estimated, in a similar way to Genet’s result [9], and it was found that the resonance was made by carbon nanotubes (CNTs); from this, we can also conclude that CNTs have good conductivity for cavity.
Analytical Study of Noise Spectral Density in -controlled Atomic Force Microscopy
이만희,안상민,제원호 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.3
Q-controlled atomic force microscopy utilizes an oscillating probe with an adjustable qualityfactor, which is done by adding a variable damping interaction to the probe. While the Q-controlcan enhance the probe sensitivity by increasing the Q-factor, the applied interaction increases thenoise of the probe motion as well. Thus, the signal-to-noise ratio (SNR) associated with the probesensitivity varies accordingly. Here, we analytically derive the noise spectral density of the tipmotion, and theoretically investigate the SNR in Q-controlled atomic force microscopy. We showthat both the overall tip-motion signal and the noise monotonically increase with the effective Qfactorunder control, whereas the SNR exhibits a global minimum near the original Q value andasymptotically scales as the square root of the effective Q-factor. Therefore, in general, the Qcontroltechnique can be used to alter the quality factor, the magnitudes of signal and noise, andthe probe sensitivity in amplitude-modulation atomic force microscopy.