• Journal of the Optical Society of Korea
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• v.18 no.6
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• pp.685-690
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• 2014

Microholographic gratings were prepared on an aluminum oxide ($Al_2O_3$) surface using a 140-fs pulse at a center wavelength of 800 nm. The $Al_2O_3$ was deposited on a silicon wafer and on indium tin oxide glass to a thickness of approximately 25 nm using an atomic layer deposition process. The silicon wafer substrate exhibited reflection-type gratings that were measured as a function of the incidence angle. The diffraction efficiency of the fabricated gratings was measured, with a maximum diffraction efficiency of 45% at an incidence angle of approximately $30^{\circ}$.

• Korean Journal of Optics and Photonics
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• v.11 no.5
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• pp.360-364
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• 2000

We demonstrate self-starting passIve mode locking of a Cr:LiSAF laser, using a SCIDlconduclor Saturable Absorber Mirror (SESAM), Two high-power red semiconductor lasers (Coherent S-67-500C-100-H) of wavelength 667 nm and maximum power of 500 mW were used as pump lasers, The cavity has 10 cm radius-ai-curvature folding minors, two SF 10 prisms, a 99% reflectivity output coupler and a SESAM at dIe focus of a 10 cm radIus-at-curvature mirror. We used the laser crystal in BrewsterBrewster shape with 1 5% $Cr^{+3}$ ion concentration and the length of 6 mm, An X-shaped resonator was used to compensate the astigmatism induced by tile crystal. The structure of the SESAM cOllSists of 30 pmr of $AlAs/Al_{0.15}Ga_{0.85}As$ layer, wi1l1 a 10 nm GaAs quantum well situated in the topmost layer Output spectra were centeled at 833 nm, with 4 nm spectral bandwidth and pulse width was measured to be 220 fs, Output power of 3 mW is obtained at a pump power of 800 mW. 00 mW.

• Journal of the Korean Magnetics Society
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• v.25 no.2
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• pp.39-42
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• 2015

After preparing carbon-doped FePt films by dc magnetron sputtering, we observed ultrafast demagnetization and its recovery by means of a time-resolved magneto-optical Kerr effect technique. We confirm that the degree of $L1_0$ ordering is decreased and coercivity is changed, as the carbon concentration increases. All samples are demagnetized within ~5 ps after the femtosecond laser pulse heated the sample. Interestingly, ultrafast relaxation time, which indicates fast magnetization recovery, increases as the carbon concentration increases due to the low spin-orbit coupling of carbon.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.317-318
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• 2013

Terahertz (THz) wave는 광학 영역과 방송파 영역 사이에 광대역 주파수 스펙트럼을 차지하고 있다. X선과는 달리 비이온화 광원으로 직진성, 투과성, 낮은 에너지 (meV)를 가지고 있어 비파괴적이고 무해한 장점을 지니고 있다. 본 연구에서는 In0.53Ga0.47As:Be/In0.52Al0.48As의 multi quantum well (MQW)을 Semi-insulting InP:Fe substrate 위에 active layer의 두께와 적층을 변화주어서 성장하였고Au (200 nm)/Ti (30 nm)의 금속전극으로 공정을 하였다. Ti:Sapphire femtosecond pulse laser를 조사하여 THz time-domain spectrometer 시스템을 이용하여 광전도검출법으로 THz 검출 특성을 연구하였다. THz 검출은 짧은 전하수명과 높은 저항을 요구한다. LTInGaAs의 경우 AsGa antisite로 인하여 짧은 전하수명을 얻게 되면 n-type의 높은 전하밀도를 가지게 되어서 저항이 낮아지게 된다. 높은 저항을 만들기 위하여 Be doping을 이용하여 과잉의 전자들을 보상하고 InAlAs layer를 삽입시켜 보다 높은 저항을 얻었다. LT-InGaAs:Be는 LT-GaAs보다 1/70 정도의 amplitude를 보이는데 LT-InGaAs/InAlAs MQW의 경우 LT-GaAs 대비 약 3/4 정도의 큰 amplitude를 얻었다. 또 active layer의 두께가 얇고 적층이 많을수록 신호가 커지는 것을 알 수 있었다. 이는 상대적으로 band gap이 큰 InAlAs층이 더 높은 저항을 만든 것으로 사료된다.

• Korean Journal of Optics and Photonics
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• v.18 no.5
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• pp.345-350
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• 2007

The characteristics of the supercontinuum generated in photonic crystal fibers were investigated by using the generalized nonlinear $Schr\"{o}dinger$ equation and the split-step Fourier method. Based on the simulated results, we generated the supercontinuum spectrum with the flatness of ${\pm}4dB$ in the wavelength range of 650 to 900 nm by employing a 200-fs pulse of Ti:sapphire laser and a commercial photonic crystal fiber.