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Biomedical subjects

Hongki Kim

Publications and source records attributed to Hongki Kim.

8 recordsLinked to original sources
PubMed2006

Microlens array diffuser for a light-emitting diode backlight system.

Microlens array (MLA) diffusers for light-emitting diode (LED) backlight systems have been developed. A high fill-factor photoresist mold for the MLA was fabricated using three-dimensional diffuser lithography, and the patterns were transferred to a nickel master mold for UV-curable polymer replication. The fabricated microlens had various paraboloidal profiles, and its aspect ratio was controlled from 1.0 to 2.1. The MLA diffuser showed a batwing radiation pattern with a radiation angle of 150 degrees. The fabricated MLA diffuser may greatly enhance the color-mixing characteristics of LED backlight systems and help reduce the number of LEDs required.

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PubMed2004

Observation of self-trapping of light in walk-off-compensating tandems.

We report the first experimental observation, to our knowledge, of the self-trapping of light in walk-off-compensating optical tandems. The experiment was conducted with picosecond light pulses in a ten-plate optically contacted tandem made of potassium titanyl phosphate prepared for phase matching along a special geometry featuring a huge local walk-off. The observation should open the door to the exploration of multicomponent soliton formation in new classes of materials and settings.

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PubMed2003

Quadratic soliton self-reflection at a quadratically nonlinear interface.

The reflection of bulk quadratic solutions incident onto a quadratically nonlinear interface in periodically poled potassium titanyl phosphate was observed. The interface consisted of the boundary between two quasi-phase-matched regions displaced from each other by a half-period. At high intensities and small angles of incidence the soliton is reflected.

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PubMed2003

Weak beam control of multiple quadratic soliton generation.

Theoretical predictions and experimental observations show that a weak harmonic seed beam can control the process of generating multiple quadratic solitons in periodically poled KTiOPO4 by inputting only a fundamental beam. This all-optical switching does not depend on the relative phase of the input beams, an unusual property for such coherent solitons.

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PubMed2003

Birth of solitons in quadratic spatial soliton collisions.

We demonstrate experimentally and theoretically the creation of a third soliton in two soliton collision processes in type I noncritically phase-matched KNbO3. The output pattern in the collision process is phase dependent, but the total energy and the relative ratio of the fundamental to the second harmonic in each soliton remain essentially unchanged to within experimental accuracy.

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PubMed2003

Observation of multiple soliton generation mediated by amplification of asymmetries.

We report the experimental observation of the formation of multiple optical quadratic solitons in a process mediated by the amplification of minute asymmetries in the diffraction properties of the input light. Experiments were conducted in phase-matched second-harmonic generation in a bulk crystal of periodically poled potassium titanyl phosphate pumped at 1064 nm. The different mechanisms that influence the process were investigated numerically, and the pulsed nature of the pump light was found to play a key role in the observed light distributions.

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PubMed2003

Quadratic spatial solitons in periodically poled KTiOPO4.

The evolution of fundamental beams into quadratic spatial solitons was investigated in a periodically poled bulk KTiOPO4 crystal near and at phase matching. Various soliton properties, such as trapping efficiency as a function of phase mismatch, poling-induced walk-off, and the effects of pulse width, beam width, and input beam quality, were measured. Effects attributed to the presence of cubic nonlinearities were also observed.

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