Development of sub-50-fs laser oscillator with mega-watt peak power for nonlinear applications
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Date
2018-09-19
Authors
Manjooran, Sujith
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Abstract
For several biomedical nonlinear applications mega-watt (MW) peak power lasers working in the near-infrared (NIR) wavelength range are desirable. A cost-effective diode-pumped sub-100-fs solid-state laser oscillator with MW peak power in the NIR wavelength range is not readily available on the commercial market. This thesis presents the successful development of several high power continuous wave (CW) and intense short pulse laser designs. Two laser gain media, namely Yb:KY(WO4)2 (Yb:KYW) and Yb: CaGdAlO4 (Yb:CALGO), were studied in this thesis. These solid-state laser crystals were end-pumped with high power diode laser at ~980 nm.
Initially, the continuous wave operation of Yb:KYW with 9W of output power at 1045 nm was demonstrated. The developed Yb:KYW had the highest slope efficiency of 77.9% when compared to all other diode-pumped Yb:KYW lasers. At the same time the developed Yb:CALGO laser was capable of delivering tunable multi-watt output power in the wavelength range of approximately 1020 nm to 1070 nm.
Based on these results two intense short pulse lasers were designed and developed in this thesis. The first one was a sub-50-fs Kerr-lens and saturable absorber (KLAS) mode-locked Yb:CALGO laser oscillator with a repetition rate of 42.3 MHz. The highest peak power achieved for 45-fs pulses directly from the oscillator was 1.7 MW. The shortest generated pulses were 38-fs with 187 kW of peak power. The second laser was a sub-100-fs Kerr-lens mode-locked (KLM) Yb:CALGO laser with a low repetition rate of 10.2 MHz. The oscillator produced 650 mW of average output power with pulse duration of 66 fs. It also generated 1 W of average power with pulse duration of 72 fs. This corresponds to pulse energy of 64 nJ with a peak power of 0.97 MW and 98 nJ with the peak power of 1.36 MW, respectively.
Some of the nonlinear applications of the high intense laser pulses were studied in the final section. Phase-matching conditions of three periodically poled crystals (PPKTP, MgO:PPcLN and MgO:PPSLT) for use in femtosecond optical parametric oscillators (OPO) to generate wavelength tunability in the NIR range were studied.
The developed intense short pulse lasers in this project have numerous applications not only in biomedical research but also in fundamental science and industry.
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Keywords
solid state laser, ultrashort pulse, Yb:CALGO