In-band pumped conical refraction lasers based on the Nd:KGd(WO4)2 crystal
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Date
2017
Authors
Howlader, Chandan Qumar
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Abstract
The laser has been used in many areas of science and technology. At the same time there are different types of lasers and conical refraction (CR) laser is one of them. Recently, there has been a strong interest in conical refraction lasers and their applications. CR lasers have the potential applications in areas like optical trapping, free space communication, super-resolution microscopy, quantum computing, cryptography, polarization demultiplexing and multiplexing, polarimetry, mode conversion and so on.
The biaxial crystal of Neodymium-doped potassium gadolinium tungstate (Nd:KGW) has been used to produce a CR laser output with in-band pumping. Unfortunately, the thermal conductivity of this crystal is relatively low which limits the high-power operation even for in-band pumping at longer wavelength which decreases the quantum defect and leads to a significant reduction of thermal load in the crystal. This thesis addressed this aspect by proposing a “passive” CR laser scheme.
In this work, we demonstrated two types of CR lasers, an active CR laser and a passive CR laser. In active CR laser the functions of laser gain medium and CR element are performed by the same crystal. In passive CR laser these functions are separated: the laser radiation is produced by one crystal and CR is done by the other. The active CR Nd:KGW laser produced and output power of 1.15 W with 32% of slope efficiency and 25.6% optical to optical efficiency. The characteristic hollow ring of the CR laser mode was not observed because the incident laser beam diameter was very large compared to the CR ring diameter supported by the crystal. For passive CR laser, Nd:KGW crystal was placed inside the Nd:YVO laser cavity and a CR ring has been seen with the proper alignment. The CR operation was confirmed by comparing the laser beam shape with a reference He-Ne laser beam passed through the Nd:KGW crystal in a separate experiment. For 10.8 W of absorbed pump power the maximum obtained CR laser output power was 3.68 W, thus demonstrating feasibility of dual crystal CR laser and its power scalability.
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Keywords
In-band pumping, Conical refraction laser, Quantum defect