Observation of spectral broadening in a commercial modelocked and Q-switched Nd:YLF oscillator - Wegner`s Demon

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We have observed spectral broadening in the pulsed output of a Quantronix model 4217 modelocked and Q-switched Nd:YLF oscillator. When Q-switched, the 76-1MHz oscillator produces a nearly gaussian train of pulses with a total energy of 3 mJ and a duration of {approximately}300 ns. Between Q-switch cycles the CW-pumped oscillator lases at a low level to enable a circulating modelocked pulse to reach steady-state transform-limited conditions. With a 1-mm intracavity etalon the steady-state modelocked pulsewidth is 150 ps and the oscillating bandwidth is 3 GHz. Measurements show that at the peak of the Q-switched train the modelocked pulse bandwidth is ... continued below

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11 p.

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Wegner, P. & Feit, M. September 14, 1994.

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Description

We have observed spectral broadening in the pulsed output of a Quantronix model 4217 modelocked and Q-switched Nd:YLF oscillator. When Q-switched, the 76-1MHz oscillator produces a nearly gaussian train of pulses with a total energy of 3 mJ and a duration of {approximately}300 ns. Between Q-switch cycles the CW-pumped oscillator lases at a low level to enable a circulating modelocked pulse to reach steady-state transform-limited conditions. With a 1-mm intracavity etalon the steady-state modelocked pulsewidth is 150 ps and the oscillating bandwidth is 3 GHz. Measurements show that at the peak of the Q-switched train the modelocked pulse bandwidth is broadened to 11 GHz, We attribute the altered spectrum to self-phase modulation (SPM) of the circulating pulse in the 3.8-cm long acousto-optic quartz modulators. SPM has been recognized as a potential problem in this type of oscillator however we did not expect to find it in a commercial product and its occurrence in the modulators rather than the rod was a surprise. Analysis of the cavity mode has determined that the spot size is small at the ends of the cavity where the modulators are located. A large mode volume in the rod coupled with a relatively small nonlinear coefficient makes intensity-dependent: phase shifts there negligible by comparison. Since the effects of SPM in this type of oscillator are not well-documented we developed a numerical model and used it to examine the spectral evolution of the circulating modelocked pulse after Q-switching. The model incorporates a rod with gain, two passive quartz blocks with nonlinear refractive index for simulating nonlinear propagation in the modulators, a time-dependent shutter to simulate the active modelocker, an etalon, and distributed Fresnel losses. The spectra that we calculate are in good agreement with that observed, confirming the source of the broadening. The oscillator has been redesigned to increase the mode size in the modulators and eliminate the SPM.

Physical Description

11 p.

Notes

INIS; OSTI as DE95016534

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  • Other Information: PBD: 14 Sep 1994

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  • Other: DE95016534
  • Report No.: UCRL-ID--119155
  • Grant Number: W-7405-ENG-48
  • DOI: 10.2172/90702 | External Link
  • Office of Scientific & Technical Information Report Number: 90702
  • Archival Resource Key: ark:/67531/metadc792209

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  • September 14, 1994

Added to The UNT Digital Library

  • Dec. 19, 2015, 7:14 p.m.

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  • Feb. 23, 2016, 3:09 p.m.

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Wegner, P. & Feit, M. Observation of spectral broadening in a commercial modelocked and Q-switched Nd:YLF oscillator - Wegner`s Demon, report, September 14, 1994; California. (digital.library.unt.edu/ark:/67531/metadc792209/: accessed October 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.