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Hollow Core Optical Fiber Gas Lasers: Toward Novel and Practical Systems in Fused Silica


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Hollow core Optically pumped Fiber Gas LASer's (HOFGLAS's) based on population inversion combine advantages of fiber lasers such as long interaction length between pump and gas medium with those of gas lasers such as high damage threshold and substantially higher thresholds for the onset of detrimental non-linear optical effects. We have recently demonstrated the first CW HOFGLAS using molecular iodine (I2) contained in a Kagome hollow-core photonic crystal fiber (HC-PCF) as the active medium. The pump near 532 nm populated a ro-vibronic level of the first excited electronic state and lasing was observed near 1.3 microns. Maximum laser output was achieved with an R=85 percent outcoupling mirror. A pump threshold of 7mW corresponding to a pump intensity of about 290 W/square cm at the fiber input was observed for optimum outcoupling. The addition of Helium buffer gas improves the lasing efficiency by a few ten percent. A phenomenological laser model can qualitatively explain the laser output power as a function of buffer gas pressure. It is a combination of pressure broadening and change of relaxation constants affecting laser saturation. The laser output mode profile suggests single-mode operation. The measured spectrum indicates lasing on multiple lines. The strongest emission originates from the terminal pump state. The lasing levels were identified using known spectroscopic data. Lasing on a single P/R doublet was observed using an intra-cavity prism as frequency selective element. The observed polarization behavior ofthe laser output as a function of pump polarization is likely a combination of coherent coupling from pump to laser and polarization dependent fiber properties. Preliminary experiments were performed toward simultaneous lasing in the visible and near infrared; lasing in the visible region is possible with suitable choice of cavity optics and configurations.



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