Optical Science and Engineering ETDs

Xuan Luo

Publication Date

7-12-2014

Abstract

Intracavity phase interferometry is sensing technique developed at UNM, in which a physical quantity to be measured is put as integral part of a mode-locked laser. It relies on the fact that any intracavity phase shift of an intracavity pulse will result in a frequency change of the whole pulse train. The implementations of IPI requires the operation of a mode-locked laser in which two pulses circulate independently, i.e. with no phase coupling between them. IPI has been demonstrated with a variety of laser systems, to detect either non-reciprocal effects (such as rotation, magnetic field), or phase changes that can be made periodic at the repetition rate of the laser cavity. The purpose of this work is to study the feasibility of applying this technique to the measurement of non-periodic (i.e. slow) changes in optical path. The new concept to measure sub-nanometer displacement uses an optoelectronic modulator (EOM) inside the cavity. The operation of the mode-locked laser after insertion of such an element in its cavity is analyzed. Several laser systems have been tried for the implementation of IPI. Two of them are presented in this thesis. The first one is a Nd:YVO4 laser, mode-locked by a multiple quantum wells (MQW) saturable absorber. The presence of a solid state saturable absorber introduced a dead band in the beat note response of the system. A new coupling between group and phase velocity was discovered experimentally, and explained through simulation. This coupling affects negatively the operation of the system, since the repetition rate is no longer a reliable fixed quantity. The coupling could be eliminated by replacing the MQW with a dye jet absorber. A first demonstration of a slow optical path change (in the nm range) was made. The system that appeared at first the most promising is the intracavity optical parametric oscillator (OPO) synchronously pumped by a mode-locked Ti:Sapphire lasers. Bringing the unstable behavior of that laser under control proved considerably more difficult than anticipated, and led to an extensive theoretical analysis of the laser. The instabilities arise from both intensity and phase fluctuations in the OPO pulse train. We simulate the second order nonlinear interactions taking place inside the nonlinear crystal of the OPO, using a new approach in the frequency domain, valid down to a few optical cycles, and taking into account the dispersion of the crystal to all orders. Phase mismatched processes draw our attention as they introduce large effective nonlinear refractive indices (creating self-phase- and crossphase- modulation) that result in a coupling of intensity and phase instabilities. A full numerical model of coupled Ti:Sapphire and OPO cavities is established by parameterizing the gain, loss, dispersion and nonlinearities. The pulse evolution of both Ti:Sapphire and OPO is examined at each cavity round trip using the ABCD matrix method in temporal domain invented in this dissertation. The simulation reproduces the observed unstable operation. However, islands of stability are found. That is an operation observed to be stable against perturbation of any of the parameters.

Degree Name

Optical Science and Engineering

Level of Degree

Doctoral

Department Name

Optical Science and Engineering

First Committee Member (Chair)

Brueck, Steven

Second Committee Member

Prasad, Sudhakar

Third Committee Member

Arissian, Ladan

Document Type

Dissertation

Language

English

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