For many years, the KGW Raman crystal has been widely used as a Raman gain medium for lasers in the visible spectrum. This paper presents recent advancements in SWIR Raman lasers, successfully implementing the KGW crystal as the gain medium in the SWIR spectral range. The KGW Raman gain coefficient is inversely proportional to the wavelength, potentially lowering the efficacy for longer wavelengths. However, the high damage threshold (exceeding 10 GW/cm2), a decent thermal conductivity coefficient as well as a highly integrated scattering cross-section effectively overcome this challenge. This paper summarizes results of different Tm based/KGW Raman lasers in external cavity configurations. Due to the KGW bi-axial properties, the Raman laser emits two discrete shifted wavelengths. The first system used a Tm:YLF pump laser and was actively Q-switched, producing short pulses of 5.4 ns. The system was the first demonstration of SWIR Raman lasing using a KGW gain medium. The second configuration used a Tm:YAP pump source and was successfully passively Q-switched using a Cr:ZnS SA resulting in output energies of 340 μJ/pulse and 450 μJ/pulse for the respective Raman wavelengths. The third Raman laser achieved a record maximum energy per pulse of 2.08 mJ for the 901 cm−1 Stokes shift utilizing a passively Q-switched Tm:YLF pump laser. To the best of our knowledge, these results present a successful demonstration of SWIR Raman conversion using KGW as the Raman gain medium, along with significant advancements in terms of conversion efficiencies and energy per pulse.
We demonstrate an external-cavity KGd(WO4)2 (KGW) Raman laser, pumped by an actively Q-switch Tm:YLF MOPA. The fundamental spectral line emitting at 1881 nm allowed the KGW bi-axial crystal to lase at two separate output spectral lines, 2198 and 2265 nm, depending on the seed polarization axis relative to the KGW's axis. The Tm:YLF seed was amplified using a double-pass Tm:YLF crystal based MOPA setup. After amplification, the seed achieved an output power of 9.15 W, and an energy pulse of 4.57 mJ, a pulse duration of 43 ns at a repetition rate of 2 kHz. The max output average power achieved for the 2265 nm was 1.85 W, with a pulse energy of 0.923 mJ at a repetition rate of 2 kHz implying a conversion efficiency of ~20.5%. We noticed a very low conversion efficiency of the shorter KGW spectral shift (at 2198 nm). The reason for this efficiency drop was validated to be the 2nd stokes forming and thus consuming the 1st stokes energy. In favor of the KGW inherent properties and according to the aforementioned results, this crystal appears to be suitable for power scaling as well as for improvement of the Raman conversion efficiency in this spectral range. The KGW crystal is well known for its use in shorter spectral wavelengths. To the best of our knowledge, it is the highest average power achieved by lasing in the 2 μm region using SRS with KGW.
Tunable and milli-Joule level pulsed Tm based laser, are demonstrated in this paper. The spectral bandwidth was narrowed down to 0.15 nm FWHM. For the Actively Q-switched Tm:YLF laser, we achieved 33 nm of tunability range between 1873 nm and 1906 nm, using a pair of YAG Etalons. Using the same tunability technic for the Passively Qswitched Tm:YAP laser, we achieved 11 nm of tunability between 1930-1941 nm. The Tm:YLF laser was actively Qswitched using an acousto-optic modulator, while achieving mJ level pulse energy along the whole tuning range at a repetition rate of 1 kHz. Up to 1.97 mJ of energy per pulse was achieved at a pulse duration of 37 ns at a wavelength of 1879 nm, corresponding to a peak-power of 53.2 kW and at a slope efficiency of 36 %. The Tm:YAP laser was Passively Q-switched using Cr:ZnS saturable absorber (SA) as modulator, achieving mJ level pulse energy along the whole tuning range. Up to 1.2 mJ of energy per pulse was achieved at a pulse duration of 24 ns at a wavelength of 1935 nm, corresponding to a peak-power of 50 kW. The combination of both high energy pulsed lasing and spectral tunability, while maintaining narrow bandwidth across the whole tunability range, enhances the laser abilities, which could enable new applications in the sensing, medical and material processing fields. Which in the case of the of the Passively Qswitched Tm laser has a major advantage in terms of foot print.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.