Pulsed green microchip lasers
Koskinen, Jesse (2026)
2026
Teknis-luonnontieteellinen DI-ohjelma - Master's Programme in Science and Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2026-05-22
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202605216104
https://urn.fi/URN:NBN:fi:tuni-202605216104
Tiivistelmä
Pulsed lasers are widely used in applications. Industrial processing, medical field, imaging and ranging all benefit from pulsed lasers due to their high intensity and short pulse duration. The requirements for specific applications are precise. A correct combination of wavelength, pulse duration, pulse repetition rate and pulse energy is often required. Mode-locked lasers offer short pulse durations with high repetition rates. However, typically the pulse energies are not that high. Q-switched lasers, on the other hand, offer high pulse energies with lower repetition rates but have the downside of longer pulse durations. Semiconductor saturable absorber mirror (SESAM) Q-switched microchip lasers can close the gap between these two technologies. Unique combinations of pulse duration, pulse energy and pulse repetition rate can be achieved.
In this thesis, two SESAM Q-switched microchip lasers were developed for the 1064 nm wavelength region. Peak powers of the order of kilowatts and pulse durations less than 150 ps were achieved in both systems. The comparison between the two devices showed that increasing the gain thickness leads to higher pulse energy and output power. However, pulse duration increased slightly due to the longer cavity length. Depending on the target application, higher output power or shorter pulse duration may be preferred.
The devices were further frequency doubled to 532 nm using a periodically poled lithium niobate (PPLN) crystal. Amplification elements were not used. The frequency doubling experiments were successful for both devices. Green output at 532 nm was generated with pulse energies of around 100 nJ. High conversion efficiencies of close to 50% were reached with a simple single-pass system. These results show that high conversion efficiencies can be achieved directly from compact microchip sources. This is due to the benefit of having high intensity output light directly from the microchip laser. This leads to an important outcome of this work, which is the compactness of the complete laser system. The design reduces alignment sensitivity, lowers cost, and eases integration into small industrial platforms. Such compact pulsed green sources are attractive for applications including time-of-flight LIDAR, Raman spectroscopy, biomedical imaging, and portable sensing systems. The results of this work show that SESAM Q-switched microchip lasers provide an efficient, compact, and versatile option for a picosecond green laser source.
In this thesis, two SESAM Q-switched microchip lasers were developed for the 1064 nm wavelength region. Peak powers of the order of kilowatts and pulse durations less than 150 ps were achieved in both systems. The comparison between the two devices showed that increasing the gain thickness leads to higher pulse energy and output power. However, pulse duration increased slightly due to the longer cavity length. Depending on the target application, higher output power or shorter pulse duration may be preferred.
The devices were further frequency doubled to 532 nm using a periodically poled lithium niobate (PPLN) crystal. Amplification elements were not used. The frequency doubling experiments were successful for both devices. Green output at 532 nm was generated with pulse energies of around 100 nJ. High conversion efficiencies of close to 50% were reached with a simple single-pass system. These results show that high conversion efficiencies can be achieved directly from compact microchip sources. This is due to the benefit of having high intensity output light directly from the microchip laser. This leads to an important outcome of this work, which is the compactness of the complete laser system. The design reduces alignment sensitivity, lowers cost, and eases integration into small industrial platforms. Such compact pulsed green sources are attractive for applications including time-of-flight LIDAR, Raman spectroscopy, biomedical imaging, and portable sensing systems. The results of this work show that SESAM Q-switched microchip lasers provide an efficient, compact, and versatile option for a picosecond green laser source.