Q-Switched and Mode Locked Short Pulses From a Diode Pumped, YB-Doped Fiber Laser

A diode-pumped, ytterbium (Yb)-doped fiber laser system was designed and demonstrated to operate in continuous wave (cw), passively Q-switched and possibly passively mode locked operation. To our knowledge, this was the first fiber laser oscillator built at the Air Force Institute of Technology. A Cr4+: YAG (Chromium: Ytterbium Aluminum Garnett) crystal was used as a saturable absorber to generate Q-switched pulses. Attempts to mode lock the laserwere performed using a semiconductor saturable absorber mirror (SESAM) and through nonlinear polarization rotation (NPR). The best output power result was 5 Watt (W) while pumping at 8.3 W, yielding 60% efficiency and peak spectral outputs between 1087-1108 nm. Passive Q-switched pulses were generated using the Cr4+: YAGcrystal with a mean width of 2.9 s and repetition rates between 60-150 kHz. This corresponded to pulse energies of 7-24 and peak powers twice as high as the average power. Q-switched and possible mode locked pulses were generated using NPR. Q-switched pulse widths ranged between 1.8-2.8 with repetition rates between 29-72 kHz. Mode locked pulse widths were 10.5 ns with a repletion rate of 17.2 MHz. Mode locking was not achieved using the SESAM, but the results that resemble mode beating are presented, and causes for error were analyzed.

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