| Abstract [eng] |
Near infrared (NIR) radiation in the 0.8 2.5 μm spectral range is highly important in modern laser physics due to its wide range of applications in fundamental research and practical fields such as strong field physics, nonlinear spectroscopy, biomedical imaging, and microscopy. Efficient implementation of nonlinear optical processes in this spectral region requires ultrashort laser pulses with high peak intensity. As pulse durations approach the few optical cycle regime, the carrier envelope phase (CEP) becomes a critically important parameter, since it defines the exact temporal structure of the electric field and strongly influences CEP sensitive phenomena such as high harmonic generation and attosecond pulse formation. In this work, the generation of high power few cycle near infrared pulses in a LiGaS₂ (LGS) crystal was experimentally investigated. A four stage optical parametric amplification (OPA) system was develop ed for broadband pulse generation and amplification at ~ 1580 n m central wavelength. In the first three stages, passive CEP stabilized seed generation was realized using supercontinuum generation in YAG and KGW crystals together with parametric amplification in BBO crystals. It was determined that the third stage produced pulses with ~1 µJ energy and covering the 1300-2000 nm spectral range, while the pulse duration reached 110 fs. A short term CEP stability of ~100 mrad was also evaluated The fourth amplification stage employed a 4.5 mm thick LGS crystal pumped by 1038 nm fundamental radiation. By optimizing the phase matching conditions and applying a 5.6° noncollinear interaction angle, a broadband signal spanning 1300-2000 nm was obtained, which support s a transform limited pulse duration of ~15 fs. A 4% energy conversion efficiency and ~24 µJ pulse energy were achieved. SFG XFROG measurements showed that the amplified pulse duration before compression was 130 fs, while the pulse exhibited dispersion com ponents of 800 fs² group delay dispersion (GDD) and 3000 fs³ third order dispersion (TOD). Pulse compression was performed using fused silica plates and by u sing a 7.5 mm thick fused silica plate, the pulse duration was compressed from 130 fs down to 24.6 fs, which corresponds to ~4.6 optical cycles at a central wavelength of ~1580 nm. It was determined that further compression was limited by third order dispersion, indicating that additional dispersion compensation techniques are required to achieve the transform limited (~15 fs) pulse duration. |
