Oc-Yeub Jeon

Broadband optical parametric amplification at the communication band with periodically poled lithium niobate

We report broadband optical parametric generation (OPG) in a single periodically poled lithium niobate crystal with a picosecond pump pulse at a fixed wavelength. We also demonstrate efficient optical parametric amplification of a broadband seed pulse within the quasi-phase-matched OPG band. The broad parametric gain band is attributed to group-velocity matching and degeneracy between the signal and idler, and the broad spectral width of the pumping source.

Efficient second-harmonic generation of ultrafast pulses in periodically poled KNbO3

Efficient second-harmonic generation of 95 fs pulses were achieved by simultaneous group-velocity matching and quasi-phase matching in a 10 mm long periodically poled potassium niobate crystal. The quasi-phase-matched bandwidth was 38 nm and second-harmonic pulse duration was 158 fs with a fundamental input pulse of 95 fs without spectral and temporal distortion in the S-band of telecommunication. Utilizing the larger off-diagonal nonlinear coefficient, d31 of potassium niobate, the conversion efficiency was significantly improved from that of periodically poled MgO-doped lithium niobate. [Appl. Phys. Lett. 82, 3388 (2003)]

Forged seal detection based on the seal overlay metric

This paper describes a method for verifying the authenticity of a seal impression imprinted on a document based on the seal overlay metric, which refers to the ratio of an effective seal impression pattern and the noise in the neighborhood of the reference impression region. A reference seal pattern is obtained by taking the average of a number of high-quality impressions of a genuine seal. A target seal impression to be examined, often on paper with some background texts and lines, is segmented out from the background by an adaptive threshold applied to the histogram of color components. The segmented target seal impression is then spatially aligned with the reference by maximizing the count of matching pixels. Then the seal overlay metric is computed for the reference and the target. If the overlay metric of a target seal is below a predetermined limit for the similarity to the genuine, then the target is classified as a forged seal. To further reduce the misclassification rate, the seal overlay metric is adjusted by the filling rate, which reflects the quality of inked pattern of the target seal. Experiment results demonstrate that the proposed method can detect elaborate seal impressions created by advanced forgery techniques such as lithography and computer-aided manufacturing.

Nondestructive imaging of hidden figures on license plates by X-ray radiograph

In this case, we investigated the modified license plates. The evidences had new embossing pressed serial numbers after erasing the original numbers on the license plates by hammering. The X-ray radiograph could visualize the hidden figures; those were virtually unseen by naked eyes or undetectable by ordinary photography. To reveal the erased figures, we performed image processing with computer software after X-ray radiographs. It proved to be an efficient nondestructive way to visualize the hidden original figures on metals.

Non-stoichiometric defect effect on coercive field in lithium niobate crystals

The internal field of lithium niobate (LN) crystal defined by the offset of the ferroelectric hysteresis loop exhibits two distinct relaxation time, suggesting that it is originated from two different types of defects due to the non-stoichiometry of the crystal. The effect of defects was verified using samples of reduced defect concentration by vapor transport equilibration method. The total amount of internal field constitutes most of the coercive field of congruent LN. The inherent coercive field of stoichiometric LN was estimated to be less than 1.5 kV/mm from the internal field measurement of congruent LN by extrapolating the relaxation effect, which was found to be fit with a stretched exponential function.

Generation of simultaneous red, green and blue light in periodically poled lithium niobate with broad quasi-phase matching band

We demonstrated simultaneous red, green and blue light generation in periodically poled lithium niobate pumped with single picosecond laser. The primary color peaks were temperature-insensitive owing to broadband optical parametric generation of participating infrared frequencies.

Broadband Optical Parametric Amplification at the Communication Band with Periodically Poled Lithium Niobate Pumped by Ps-Laser Pulse

We report broadband optical parametric generation (OPG) in a single periodically poled lithium niobate crystal with a picosecond pump pulse at a fixed wavelength. We also demonstrate efficient optical parametric amplification of a broadband seed pulse within the quasi-phase-matched OPG band. The broad parametric gain band is attributed to group-velocity matching and degeneracy between the signal and idler, and the broad spectral width of the pumping source.

Broadband Optical Parametric Amplification in a Periodically Poled LiNbO 3 Crystal by ps-Pulse Pump

We report broadband optical parametric amplification in a single periodically poled LiNbO 3 crystal pumped by a 35 ps pulse at a fixed wavelength of 870 nm.

Amplified Spontaneous Emission in Organic Solids Composed of Excited-State Intramolecular Proton Transfer Molecules

Amplified spontaneous emission associated with excited-state intramolecular proton transfer was investigated in organic single crystals and glasses. The closely packed single crystals were shown to be a promising candidate for gain medium for pulsed excitation.

Amplified spontaneous emission and two-photon fluorescence in an organic single crystal composed of excited-state intramolecular proton transfer molecules

Low-threshold amplified spontaneous emission of blue fluorescence was observed in an organic single crystal composed of excited-state intramolecular proton transfer molecules. The two-photon absorption spectrum has also been measured for efficient upconverted blue emission.