Seth M. Swift

Date of Award


Document Type


Degree Name

Master of Science


Department of Engineering Physics

First Advisor

Matthew J. Bohn, PhD


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 laser were performed using a semiconductor saturable absorber mirror (SESAM) and through nonlinear polarization rotation (NPR). The best output power result was 5 Watts (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+:YAG crystal with a mean width of 2.9 μs and repetition rates between 60-150 kHz. This corresponded to pulse energies of 7-24 μJ 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 μs 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.

AFIT Designator


DTIC Accession Number