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Sub-100 ps Light Sources Based on Q-Switched Microchip Lasers

Research output: Book/ReportDoctoral thesisCollection of Articles

Details

Original languageEnglish
PublisherTampere University of Technology
Number of pages50
ISBN (Electronic)978-952-15-4058-5
ISBN (Print)978-952-15-4047-9
Publication statusPublished - 22 Nov 2017
Publication typeG5 Doctoral dissertation (article)

Publication series

NameTampere University of Technology. Publication
Volume1511
ISSN (Print)1459-2045

Abstract

Laser pulses are instrumental for a wide range of applications in advanced measurement and imaging techniques, such as time-gated Raman spectroscopy or fluorescent lifetime measurements. Key features for these applications are the relatively high peak power, high pulse energy, and a short pulse duration. To this end, the goal of the thesis has been to demonstrate novel light sources emitting optical pulses with sub-100 ps duration at UV, visible, and infrared wavelengths. The sub-100 ps optical pulse regime fills a gap between the more complex mode-locked lasers and typical Q-switched microchip lasers, which emit optical pulses with duration longer than 300 ps. In particular, key efforts were allocated to developing Nd:YVO4 microchip lasers, emitting either at 1064 nm or 1342 nm, and employing semiconductor saturable absorber mirrors for passive Q-switching. The typical pulse duration was ∼100 ps at 1064 nm and ∼200 ps at 1342 nm. Typical repetition rate was in 100 – 500 kHz range corresponding to average powers of several mW. These laser pulses were amplified in compact Nd:YVO4 amplifiers up to an average power of 1.3 W. Then nonlinear wavelengths conversion techniques were employed to expand the emission wavelength and also to attain further pulse shortening.

State-of-the-art results have been achieved on several fronts of research. First of all, in this work the first Q-switched microchip lasers based on GaInNAs semiconductor saturable absorber was developed. Using second harmonic generation, we have achieved leading values for average power, pulse energy, and pulse duration for emission at 671 nm, and 532 nm. Using third harmonic generation we demonstrated emission at 355 nm and using frequency quadrupling we attained emission at 266 nm. Finally, in this work demonstrated the first picosecond diamond Raman laser pumped at 532 nm with sub-100 ps Q-switched pulses. Owing to favorable combination of pulse energy and pulse duration, we attained efficient operation of the Raman laser with emission at yellow (573 nm); the output pulses were as short as 39 ps and the output power was 143 mW, corresponding to a conversion efficiency as high as 40%. In another approach, we demonstrated Raman laser operating at 1240 nm by pumping with 1064 nm Q-switched pulses. In this case, Raman conversion resulted in optical pulses with a duration of 62 ps and 246 mW average power, which were frequency doubled to 620 nm. The corresponding pulse duration and average power at 620 nm were 46 ps and 128 mW, respectively. As third approach, under intense pumping the 620 nm was also generated directly from 532 nm, with 10 mW of average power and 24 ps pulse duration, the shortest pulses achieved in this work.

The results open a new perspective to the development of practical laser sources delivering µJ-level short optical pulses. When combined with nonlinear conversion techniques, the technology platform covers an extensive wavelength range and could find uses in a wide range of applications; for example, the 532 nm laser platform has been used successfully in time-gated Raman spectroscopy.

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