Korean Journal of Optics and Photonics (한국광학회지)

Optical Society of Korea (한국광학회)
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Generation of Femtosecond Pulses in a Passively Mode-Locked 100 MHz Cr4+:YAG Laser

수동 모드 잠금된 100 MHz Cr4+:YAG 레이저에서의 펨토초 펄스 발생

  • Cho, Won-Bae (Department of Molecular Science & Technology Ajou University) ;
  • Rotermund Fabian (Department of Molecular Science & Technology Ajou University) ;
  • Kim, Jong-Doo (Department of Physics Chungnam National University) ;
  • Jeon, Min-Yong (Department of Physics Chungnam National University) ;
  • Suh, Ho-Suhng (Length group, Division of Optical Metrology Korea Research Institute of Standards and Science)
  • 조원배 (아주대학교 분자과학기술학과) ;
  • 이상민 (아주대학교 분자과학기술학과) ;
  • 김종두 (충남대학교 물리학과) ;
  • 전민용 (충남대학교 물리학과) ;
  • 서호성 (한국표준과학연구원 길이그룹)
  • Published : 2005.12.01
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Abstract

We report on the development of a passively mode-locked near-infrared femtosecond laser with Cr:YAG crystal that operates near room temperature. The laser wavelength could easily be tuned by using only the internal prism pair over 110 nm from 1400 nm to 1510 nm in cw and over about 30 nm in mode-locked operation, respectively Maximum cw output powers of 810 mW were obtained with $1.5 \%$ output coupler for absorbed pump powers of 7.6 W. For compensation of the internal group velocity dispersion, an IR graded prism pair was used. The Cr:YAG laser delivered nearly Fourier-transform limited pulses with a pulse duration as short as 64 fs at 100 MHz repetition rate. In the mode-locked regime, the laser was operating at 1510 nm with a spectral bandwidth of 44 nm. In order to avoid unstable mode-locking and power instabilities, self-built tubes were inserted into the beam path in the resonator and purged with N2 gas. Finally, output powers of the Cr:YAG laser were optimized to 250 mW fer long time stable mode-locked operation.

$Cr^{4+}:YAG$ 레이저 매질을 사용하여 실온영역에서 안정적으로 수동 모드 잠금된 근적외선 펨토초 레이저를 제작하고, 그 특성을 분석하였다. 공진기 내부에 설치된 프리즘의 조절만으로 손쉬운 파장 조절이 가능하였으며, 연속 발진시 1400 nm부터 1510 nm까지 110 nm 정도, 모드 잠금 경우 1500 nm 부근에서 30 nm 정도의 파장 조절이 가능함을 확인하였다. $1.5 \%$의 투과율을 지닌 출력거울을 사용하였으며, 연속 발진시 흡수 파워가 7.6 W 일 때 최대 810 mW 이상의 출력을 측정하였다. 공진기 내에서 발생된 분산을 보상하기 위하여 적외선용 프리즘 쌍을 사용하였으며, 100 MHz의 반복률에서 푸리에 변환한계에 근접한 64 fs의 극초단 펄스 방출이 가능하였다. 레이저의 중심파장이 1510 nm 일 때 스펙트럼의 반치폭은 44 nm였다. 모드 잠금이 꺼지지 않고 장시간 안정적으로 작동이 가능한 레이저 제작을 위해 공진기 내부의 광 경로에 관을 설치하고 질소가스를 순환시켰으며, 평균출력 250 mW로 최적화하였다.

Keywords

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