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40펨토초 미만 펄스폭의 고출력 파장가변 티타늄사파이어 레이저
임용식,노영철,이기주,김대식,장준성 한국광학회 1999 한국광학회지 Vol.10 No.5
근적외선 파장영역에서 시분해 분광용 레이저 광원개발을 위해 발진파장이 반사경의 파장 선폭에 의해 제한된 수십 펨토초 펄스폭의 고출력 티타늄 사파이어 레이저를 개발하였다. 한쪽 프리즘 끝에 미세 stepping-motor로 제어되는 kniff-edge slits를 사용하여 발진파장을 선택하였으며, 파장가변영역은 770nm~870nm이었고, 이 파장영역에서 얻은 펄스폭은 40 fs 미만이었다. 가장 짧은 펄스폭은 약 17 fs 이었으며 이때의 파장중심은 820nm이고 선폭은 72nm이었다. 약 5W 출력의 아르곤 레이저 여기광을 사용하여 위의 파장영역에서 얻은 평균출력은 440 mW~580 mW 이었다. 연속발진 경우와 Kerr-lens mode locking 경우의 이득매질에서의 빔의 크기를 계산하여 이득변조값 ${\lambda}=2.5{\times}10_{-8}$ W을 수치적으로 얻었고, 이로부터 Ginzberg Landau 방정식을 사용하여 40 fs 미만의 펄스폭이 발생됨을 보였다. We have utilized soft-aperturing by gain media to develop a high-power tunable Ti:Sapphire laser with sub-40-fs and broad tuning range. The tunable spectral range was only limited by the bandwidth of mirrors. We made use of knife-edge slits near an intra-cavity prism controlled by micro-stepping-motors to tune the center wavelength continuously. The tunability of the center wavelength was ranged from 770 nm to 870 nm, and the measured pulsewidth was sub-40 fs throughout the above spectral range. The shortest pulsewidth was about 17 fs at the center wavelength of 820 nm and the spectral bandwidth was 72 nm. At 5 W pumping power of the Ar-ion laser we obtained average output power of 440 mW~580 mW. For the cw and Kerr-lens mode-lodking conditions, we have evaluated the value of an amplitude modulation to be ${\gamma}=2.5{\times}10^{-8}/W$ from the calculated waists of a Gaussian beam on the Ti:sapphire crystal surface. Using this result we demonstrate that the generation of sub-40-fs Kerr-lens mode-locked pulse can be described by the Ginzberg-Landau model which is a weak pulse shaping model.
임용식 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.1
We report the analysis of coherent phonon oscillations of radial breathing modes (RBMs) in micelle-suspended CoMoCAT single-walled carbon nanotubes excited by the lowest E_(11) optical transition in the near-infrared from 1.23 to 1.71 eV. We compare two spectral analyses: fast Fourier transformation (FFT) and linear prediction singular value decomposition (LPSVD). In contrast to the FFT method, the LPSVD spectral analysis has the following advantages: excellent signal-tonoise ratio, no need for the data preprocessing, and a reliable table of frequencies, amplitudes, time constants and phases of each sinusoidal component in the signal. We also illustrate the full details of extracting a reliable set of sinusoidal signals to obtain resonance excitation profiles for coherent phonons. The LPSVD reveals the abundance of strong exciton-phonon coupling in cabon nanotubes with a 1-D structure.
임용식,Stephen K. Doorn,Erik H. H´aroz,Robert H. Hauge,Ji-Hee Kim,주니치로코너,Jonah Shaver,Richard E. Smalley,이기주 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.I
We report on a new high-resolution optical spectroscopy, coherent phonon measurement, for determining the chiral index of carbon nanotubes. Using femtosecond pump-probe spectroscopy, we demonstrate the real-time observation of lattice vibrations in individualized single-walled carbon nanotubes in an aqueous surfactant solution. Almost all available radial breathing modes in the Fourier transform spectrum from coherent phonon oscillations are well-resolved with less ambiguity in comparison to continuous-wave resonant Raman scattering.