We demonstrate a common diode-pumped Q-switched Tm/Ho composite laser with a developed compact hybrid cavity, where the lasing wavelengths were changeable between Ho laser and Tm laser via modulating the cavity losses by changing transmittances of the crystalline Cr:ZnSe saturable absorbers (SAs) or using the output couplers between broad band coating and narrow band coating. Using a common 808 nm diode laser as the pump source, maximum Q-switched Ho laser power of 707 mW at 2091 nm, with pulse energy of 50.7 μJ and peak power of 99 W at 13.4 KHz was obtained among using the NCs. Among the BCs, maximum Q-switched Tm laser power of 413 mW at 2011 nm, with pulse energy of 35 μJ and peak power of 104 W at 11.7 kHz was obtained. Combing both advantages of Tm laser and Ho laser, a wide scope of applications including detection, commutation, and medical treatments are expected from the proposed laser source due to its accessibility, multifunction and miniaturization.
We present a compact diode-pumped Tm/Ho:YLF laser, via integrating the Tm-doped and Ho-doped YLF crystals into a single bulk gain medium. Gain spectral model was developed first to the predict the potential Tm:YLF laser wavelength using different types of output coupling, for enhancing resonant absorption of the Ho:YLF crystal. Further verification were carried out by intra-cavity pumping the Ho:YLF laser with a Tm:YLF laser, where maximum output power of 11.3 W at 2.06 μm with near diffraction limited beam quality was obtained with conversion efficiency of 28.2% by considering the incident 793 nm diode power. In the Tm/Ho:YLF laser, maximum output power of 10.2 W at 2063 nm with power instability of 0.55% was obtained, corresponding to a slope efficiency of 29.6 % and optical conversion efficiency of 25.5%. The results provide a compact, accessible, and efficient Ho laser scheme, with has potential applications in wind lidar, surgeries, material processing, and nonlinear frequency conversion toward the mid-infrared region.
We firstly demonstrated an obtainable Ho:YAP laser intra-cavity pumped by a diode-pumped Tm:YAP laser. A common 792 nm AlGaAs fiber coupled laser diode was used to pump the a-cut Tm:YAP crystal. In the Tm laser experiment, a maximum output power of 1.9 W at 1958.4 nm was obtained, corresponding to a slope efficiency of 12.1 %. In the Ho laser experiment, a maximum output power of 1.1 W at 2118.2 nm was obtained with a slope efficiency of 8.9% for 21.9 W diode incident pump power on the Tm:YAP crystal. At the maximum output power of the Ho laser, beam quality factor (M2) was measured to be 1.79 and 1.72 in the horizontal and vertical directions, respectively. Further improvement in the performances of the current Ho:YAP laser is predictable via direct producing a more compact gain module by adhesive-free bonding of Ho:YAP to Tm:YAP crystals.
We demonstrate passively Q-switching in a 2.1 μm Tm/Ho composite laser via developing a hybrid cavity to separate the intra-cavity Tm laser from modulated by the saturable absorber (SA). Enhancement in Ho laser efficiency was demonstrated in the proposed hybrid cavity, compared with the common two-mirror laser resonator. Using the crystalline Cr:ZnSe SA, maximum average output power of 553 mW at 2090 nm under absorbed 808 nm LD power of 6 W was obtained at pulse repetition rate of 9.5 kHz. Using layered WSe2 SA fabricated with the CVD process, maximum Ho laser power of 141 mW with pulse width of 185 ns at a repetition rate of 33 kHz was obtained. The current gain medium could be replaced with other hosts such as YVO4, YLF, and YAP with natural birefringence, which facilities a potential polarized pulse Ho laser. Also, the current SAs could also be replaced by other nanomaterials with controllable broadband saturable absorption such as gold nanorods,topological insulators and carbon nano tube for seeking novel pulse Ho lasers.
We developed a compact 2-μm intracavity-pumped Ho : YVO4 laser using a diode-pumped Tm:YAP laser at room temperature. Before applying the Ho laser, the lasing characteristics of the a-cut Tm:YAP laser were studied, and a maximum output power of 2.76 W at 1951.6 nm was obtained under an incident laser diode pump power of 25 W with a slope efficiency of 15.8%. Under the same cavity structure, the continuous-wave Ho : YVO4 laser yielded a maximum output power of 1.7 W at 2052.7 nm for an incident diode pump power of 29 W, corresponding to a slope efficiency of 10.4%. The beam quality factor (M2) of the Ho : YVO4 laser at the maximum output power was estimated to be 1.16 and 1.26 in the horizontal and vertical directions, respectively, which indicates the occurrence of near-diffraction-limited beam propagation.
We demonstrate a 2.1 μm Tm/Ho composite laser via diffusion-bonding the Tm-doped and Ho-doped YAG crystals into a single bulk structure, which facilitates the direct use of common AlGaAs diode lasers (LD) for an efficient and compact Ho laser source at room temperature. Locking the pump wavelength at absorption peak of 784.9 nm of the Tm-doped region of the composite gain medium, maximum output power of 6 W at 2122 nm was obtained with a slope efficiency (SE) of 40.1% and conversion efficiency (CE) of 33.6% from absorbed LD power to Ho laser, which is comparable in efficiency with the 1.9 μm LD resonantly pumped Ho lasers. Above 1.6 W Ho laser power at operation temperature range from 9 °C to 27 °C could also be realized by side-pumping absorption band of the Tm-doped region at 808 nm, which indicates a 40 nm broad pump wavelength range for the Ho laser at room temperatures. Via broad-band coating the output coupler with the same transmittance from 2000 nm to 2100 nm, synchronous Tm laser and Ho laser oscillation at both 2.1 μm and 2 μm was observed, where signal of the Tm laser was faded finally with the increased pump power. Furthermore, thermal lens and temperature distribution of the composite gain medium is analyzed basing on a proposed thermal model recently.
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