Abstract
We demonstrate a direct diode-pumped passively Q-switched (PQS) Tm/Ho composite laser with a developed compact hybrid cavity, where the lasing wavelengths were changeable from Ho laser to Tm laser via decreasing initial transmittance of the crystalline Cr:ZnSe saturable absorbers (SAs) from 95%, 92%, to 89%. Using a common 808 nm diode laser as the pump source, maximum average output power of 390 mW, maximum pulse energy of 39 uJ, and the shortest pulse with a full width at half maximum of 22 ns were obtained at lasing wavelengths of 2122 nm, 2090 nm, and 2011 nm respectively, where these peak wavelengths remained stable during the PQS processes with different SAs.
Highlights
Tm lasers and Ho lasers are attractive in a variety of applications including radar systems, medical treatment, environmental monitoring, and macromolecular material processing, owing to the lasing wavelengths which match well with the transparent atmosphere window, strong absorption band of biological water, and the moderate absorption band of organic polymers at 2 μm [1]–[3]
Before inserting the saturable absorbers (SAs), maximum CW power of 781 mW at absorbed 808 nm LD power of 8.03 W was obtained with slope efficiency (SE) of 14.6% (Fig. 2), where peaks of the lasing wavelength were at 2122.1 nm and 2129.7 nm, respectively
We have illustrated the wavelength-changeable phenomenon in a passively Q-switched (PQS) Tm/Ho composite laser, where the lasing wavelength was changeable from Tm laser at 2011 nm to Ho lasers at 2090nm and 2122 nm, respectively via decreasing the initial transmittance of the Cr:ZnSe SA
Summary
Tm lasers and Ho lasers are attractive in a variety of applications including radar systems, medical treatment, environmental monitoring, and macromolecular material processing, owing to the lasing wavelengths which match well with the transparent atmosphere window, strong absorption band of biological water, and the moderate absorption band of organic polymers at 2 μm [1]–[3]. Tm lasers had been well demonstrated with high lasing efficiencies [9] and high output powers [10], [11], owning to the theoretical “2 for 1” cross-relaxation process [8] and the existing absorption peaks which are within emission bands of the mature AlGaAs LDs. the lack of absorption. Since additional cryogenic device should be equipped for suppressing the intense up-conversion process [13], Tm, Ho co-doped lasers were not suitable for room-temperature operation. In-band pumped Ho lasers got intensively researched to date and became a main way for Ho lasers [6], [16], with the development of 1.9 μm lasers such as the GaSb LD [17], Tm-doped fiber and bulk lasers [10], [18]
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