Ph.D. Oral Examination - David S. Hum - Feb. 15, 2007

David Hum dhum at
Tue Feb 13 11:28:46 PST 2007

Title: Frequency conversion in periodically poled, near-stoichiometric
lithium tantalate fabricated by vapor transport equilibration

David S. Hum
Department of Electrical Engineering
Stanford University

Adviser : Professor Martin M. Fejer

Date : Thursday, February 15, 2007

Time : 11:00am (Refreshments at 10:45am)

Location : CIS-X Auditorium


Frequency conversion using quasi-phasematched (QPM) nonlinear devices is
efficient and engineerable. One method of quasi-phasematching can be
realized by periodically poling ferroelectrics. Lithium tantalate, like many
ferroelectrics, is limited in application by photorefractive damage (PRD) in
the commonly available, congruently melting composition.
Vapor-transport-equilibrated, near-stoichiometric lithium tantalate (VLT)
has been shown to have reduced defect concentrations and increased
photoconductivity. Because of the two-order of magnitude increase in
photoconductivity, VLT has improved resistance to PRD and has been used to
demonstrate efficient and stable frequency conversion at high average
powers. QPM devices based on VLT have allowed the demonstration of near
room-temperature generation of visible light. Generation of 10 W of CW
532-nm radiation by second harmonic generation from 29 W of 1064-nm
radiation has been demonstrated in a 4-cm-long device. Devices periodically
poled for generation of 589-nm radiation by both second harmonic and sum
frequency generation have also been demonstrated as near room temperature,
multi-watt sources. Control of the ferroelectric properties allowed periodic
poling down to a period of 5 microns, suitable for generation of 458.3-nm
radiation by second harmonic generation. Investigations into the application
of periodic poling and vapor transport equilibration on rotated-cut VLT
crystals have led to the development of aperture-scalable,
quasi-phasematched devices suitable for high peak- and average-power
nonlinear optics.

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