HWAN HONG LIM

• PhD
• Principal Engineer at HyTILA corporation

We demonstrated a flat-convex unstable cavity Nd:YAG/Cr⁴⁺:YAG ceramic air-cooled microchip laser (MCL) generating a record 37.6 and 59.2 MW peak power pulses with an energy of 17.0 and 24.1 mJ and a width of 452 and 407 ps at 20 Hz by using a uniform power square and hexagon pump, respectively. For hexagon pump, the near field hexagon donut beam wa...

A doughnut mode microchip laser was demonstrated by introducing a monolithic ceramic Nd:YAG/Cr⁴⁺:YAG chip in an unstable resonator to deliver laser pulses with an energy of 13.2 mJ and a pulse width of 476 ps, corresponding to a record peak power of 27.7 MW. The laser beam quality was characterized by M²∼6 at 10 Hz repetition rate. No significant d...

We first demonstrated a continuously and widely giant-pulse duration tunable laser based on a short monolithic Nd:YAG/Cr:YAG ceramic by cavity-length control in 100 Hz operation. The tuning range of pulse duration τ was from 0.5 to 9 ns as keeping peak powers of over 0.5 MW up to 6 MW. The characteristics of the ceramic laser was discussed in detai...

We present an unstable cavity Nd:YAG/Cr ⁴⁺ :YAG microchip laser generating pulses with an energy of 17 mJ and a duration of 452 ps at 20 Hz repetition rate, corresponding a record peak power of 37.6 MW.

Formation dynamics of laser-induced periodic surface structures (LIPSSs) on the SiC substrates were described with varying pulse numbers and pulse duration. As the number of laser pulses increases, two significant transformations become evident in the progression of structural formations. First from surface roughening with nanoparticles to LIPSS wi...

The synthesis of gold nanoparticles (Au NPs) was carried out by utilising the pulsed laser ablation in liquids (PLAL) method with a microchip laser (MCL) system. This portable system features low power consumption and a giant-pulse laser. Aqueous solutions with and without the surfactant poly(N-vinyl-2-pyrrolidone) (PVP) were used for laser ablatio...

Design of a high-brightness 1064 nm laser is presented. It deals with passively-Q-switched lasers’ timing-jitter through injection seeding, with pulse-to-pulse energy instability by amplification in saturated regime and with thermal effects in amplifier using Distributed-Face-Cooling.

A passively cooled Nd:YAG/Cr ⁴⁺ :YAG unstable resonator microchip laser achieves a record-breaking brightness of 300 TW/(sr·cm ² ) with 26.4 MW peak-power, 10.5 mJ energy, 398 pS pulse duration, and M ² of 2.7 at 10 Hz repetition rate.

We present an air-cooled Nd:YAG/Cr ⁴⁺ :YAG microchip laser with unstable resonator generating a record peak-power of 71.9 MW (22.54 mJ, 313.5 ps) and 82.8 MW (26 mJ, 314 ps) at 100 and 80 Hz, respectively.

Both record 59.2 MW peak power (24.1 mJ, 407 ps) and record 0.736 PW/(sr∙cm ² ) (effective) brightness air-cooled Nd:YAG/Cr ⁴⁺ :YAG ceramic microchip laser with unstable resonator is presented.

Radiation dose rate effects on the properties of a compact fiber-optic laser-induced breakdown spectroscopy (LIBS) system with a monolithic Nd:YAG/Cr:YAG composite ceramics were investigated for remote analysis in a hazardous environment. To investigate radiation effects on the LIBS signal, properties related to the Nd:YAG laser operation such as o...

In this study, a compact fiber-optic laser-induced breakdown spectroscopy (LIBS) system was developed using a microchip laser (MCL) with a monolithic Nd:YAG/Cr:YAG composite ceramic, for remote analysis of hazardous environments, such as nuclear reactor cores. Short duration laser pulses exhibiting a near-Gaussian beam profile were obtained. The ou...

Brightness scale of microchip laser was achieved by introducing unstable cavity allowing steady pulse width and 2. A record effective brightness of 0.5 PW/(sr∙2) and 4 times longer effective Rayleigh length than Gaussian were observed.

High brightness microchip-lasers were frequency-doubled using single LBO crystals under high dose-rate gamma-ray irradiation for the first time. Dose-rate dependent exponential-decay of SHG-energy was observed for one-hour continuous operation at dose-rates up to 10 kGy/h.

We present a high-brightness doughnut beam laser based on a passively Q-switched monolithic Nd:YAG/Cr:YAG ceramic microchip laser with unstable cavity having the pulse- energy of 8.3 mJ, pulse-width of 570 ps, and M2 value of 2.

The change of pulse-width scaling law of air-breakdown threshold intensity at sub-nanosecond region is discussed for an optimum pulse-width for laser ignition. Timing of plasma creation depending on pulse-energy is also discussed.

We demonstrate sub-ns pulse-width tunable microchip laser by cavity-length control and double-pass Nd:YAG ceramic amplifier for investigation of optimum-pulse laser ignition. The change of pulse-width scaling law of air-breakdown threshold is investigated at different pressures.

We present a compact, high peak-power, and widely pulse-width tunable monolithic Nd:YAG/Cr:YAG ceramic micro laser by cavity-length control. Pulse-width dependent fluence threshold of air-breakdown is investigated in sub-ns region showing a local breakdown threshold.

Quantum information technologies harness the intrinsic nature of quantum theory to beat the limitations of the classical methods for information processing and communication. Recently, the application of quantum features to metrology has attracted much attention. Quantum optical coherence tomography (QOCT), which utilizes two-photon interference be...

We demonstrated CW SHG at 400 nm in a first-order QPM adhered slab waveguide with a periodically-poled Mg-doped stoichiometric lithium tantalate core. The measured SHG normalized conversion efficiency was 34.7%/W for a 20 mm length.

NLO waveguide based on low-absorption Mg:SLT is presented for efficient wavelength conversion. GaN-laser-pumped optical parametric generation produces arbitrary spectral components and shapes in the visible to near infrared range by designing QPM structures.

We demonstrated optical parametric generation (OPG) pumped by GaN diode laser in nonlinear optical waveguide. Mg:SLT-based slab waveguide emits visible photons with RGB spectrum and degenerate photon pairs in 800 nm region with controlled bandwidth.

We investigate light-induced heating by nonlinear absorption in LiNbO3-type crystals under continuous-wave (CW) laser irradiation. The heat source is one-photon absorption by long-lived excited states created by two-photon absorption. The accumulated effect of excited states, which act as light absorbers, is significant for a CW laser. Light-induce...

Quantum optical coherence tomography can realize high-resolution imaging with dispersion tolerance by virtue of quantum entanglement. We generate ultrabroadband spontaneous parametric fluorescence from chirped quasi-phase matching devices to achieve the ultrahighresolution imaging.

We analyze a solution of the heat equation for second harmonic generation (SHG) with a focused Gaussian beam and simulate the temperature rise in SHG materials as a function of the second harmonic power and the focusing conditions. We also propose a quantitative value of the heat removal performance of SHG devices, referred to as the effective heat...

Nonlinear absorption – such as green-induced infrared absorption (GRIIRA) – increases the risk of the catastrophic damage during high peak- power wavelength conversion. We propose a novel concept to suppress parasitic green second-harmonic generation (SHG) in optical parametric oscillation (OPO) using specially engineered quasi-phase-matched (QPM)...

Parasitic green light has been a trigger of the damage in 1um-pumped OPO through GReen-Induced InfraRed Absorption (GRIIRA). A phase-reversed-cluster QPM device suppresses unwanted green light while maintaining OPO performance.

We examine thermal in single pass CW SHG depending on focusing conditions. Temperature increase in crystals and thermal lensing effect are investigated by the effective heat capacity of devices, which is ruled by focusing conditions.

We report the observation of the broadest frequency correlation of two-photon states to date via parametric down conversion using chirped QPM device. The two-photon correlation in time domain can be compressed to 3.3 cycles.

Thermal management is discussed in single-pass CW SHG in QPM Mg:SLT. Effective heat capacity in four-side heat removal module is quantitatively characterized by Phase-Matched Calorimetry and enhanced by 50% with narrowing device width.

We report sum-frequency-photon generation from an entangled photon pair, which is an important step toward the realization of photon pairs with ultra-short (monocycle) temporal correlation.

Mg-doped stoichiometric lithium tantalate (SLT) is a promising material in high power generation, due to its high thermal conductivity. The accuracy of the temperature-dependent Sellmeier equation for Mg-doped SLT is important for designing high-power-frequency converters. We propose a temperature-dependent Sellmeier equation for the extraordinary...

Compressing the temporal correlation of two photons to the monocycle regime (3.56 fs, center wavelength: 1064 nm) is expected to open up new perspectives in quantum metrology, allowing applications such as submicron quantum optical coherence tomography and novel nonlinear optical experiments. To achieve this, the two-photon state must essentially b...

We present thermal effects in single pass CW SHG with focused Gaussian beams. Thermal dephasing and lensing effects depending on the SH power are demonstrated with the calculated temperature change in PPMgSLT crystals.

Quantum entanglement of two photons created by spontaneous parametric downconversion (SPDC) can be used to probe quantum optical phenomena during a single cycle of light. Harris [Phys. Rev. Lett. 98, 063602 (2007)] suggested using ultrabroad parametric fluorescence generated from a quasi-phase-matched (QPM) device whose poling period is chirped. In...

Quantum entanglement of two photons created by spontaneous parametric downconversion (SPDC) can be used to probe quantum optical phenomena during a single cycle of light. Harris [Opt. Express 98, 063602 (2007)] suggested using ultrabroad parametric fluorescenc generated from a quasi-phase-matched (QPM) device whose poling period is chirped. In the...

We investigated the structures, photoluminescence (PL), and lasing characteristics of ZnO nanorods prepared by chemical bath deposition. The PL spectra under picosecond-laser-pulse excitation exhibited a spectrally narrowed emission band with a peak at 3.20 eV and a spectral width of 35 meV. The lasing phenomena are ascribed to the amplified sponta...

We proposed a method to determine device quality in heat removal. Temperature change depending on SH power was analyzed by fitting with a new model to characterize heat removal performance of SHG modules, named as phase-matched calorimetry (PMC). The thermal disposal performance of SHG devices was improved by combination of metal housing and reduce...

We investigated thermal properties depending on boundary conditions of wavelength conversion crystals. With a tight aperture, we demonstrated 19-W single-pass 532-nm SHG at a conversion efficiency of 26.5% in a 10-mm-long PPMgSLT crystal without saturation.

In this paper, we introduce the experiment which gives the ultra-broadband parametric fluorescence from chirped-QPM device which extends approximately from 790nm to 1600nm towards the generation of mono cycle frequency-entangled photon pairs. The sample is 2cm-long SLT crystal with the magnesium oxide concentration of 1.0mol-% (MgSLT). Compared wit...

In this study, we investigated the structures, photoluminescence (PL), and lasing characteristics of the ZnO nanorods prepared by using chemical bath deposition. The continuous-wave HeCd laser-excited PL spectra of the ZnO nanorods exhibited two emission bands, one in the UV region and the other in the visible region. The UV emission band has its p...

We investigated normalized conversion efficiency depending on pump linewidth in cw single-pass QPM SHG. A maximum normalized SHG conversion efficiency is observed around a pump linewidth of 0.03 nm by additional SFG between longitudinal modes.

We fabricated a 2 mm-thick periodically-poled lithium niobate (PPLN) by direct bonding of two 1 mm-thick PPLNs. A broad spectral range of quasi-phase matched secondharmonic generation was demonstrated by angular tuning.

We fabricated 1 mm-thick periodically-poled lithium niobate (PPLN) crystals by using a high-voltage amplifier for standard electric field poling combined with a voltage multiplier. Furthermore, two 1 mm-thick PPLNs were directly bonded to make a 2 mm-thick PPLN. The large aperture allowed broad angular tuning, and a broad spectral range of quasi-ph...

We developed a simple and accurate method for measuring the refractive indices of transparent plates by analyzing the transmitted fringe pattern as a function of angle of incidence. By using two different wavelengths, we resolved the 2pi- ambiguity inherent to the phase measurement involving a thick medium, leading to independent determination of t...

We developed an accurate and efficient method for measuring the refractive indices of a transparent plate by analyzing the transmitted intensity versus angle of incidence. By using two different wavelengths, we resolved the 2π-ambiguity inherent to the phase measurement involving a thick medium, leading to independent determination of the absolute...

We derived an expression for the noise between the diffraction orders from a random grating. The result was applied to analyze the statistical duty-cycle error in PPLN, providing an efficient means for poling quality evaluation.

We investigated Fabry-Perot type interference from optical wafers to measure the refractive indices. This method is accurate (~10-5 for fused silica), insensitive to environmental perturbation, and simple to implement, compared to the conventional indexmeasurement methods.

Quasi-phase-matching devices are usually fabricated by electric field poling over photolithographically defined electrode patterns on ferroelectric crystal substrates. For the optimal nonlinear optical performance of such devices, the micro-poled domain structure must ensure good fidelity to the designed grating structure. We present a nondestructi...

In 1892 Drude and Nernst reported the first observation of a standing light wave by using a fluorescent thin film, which is a real-time version of Wiener's first experiment on standing light wave. We reproduce the experiment by Drude and Nernst with improved efficiency using modern laser technology and a highly fluorescent π-conjugated polymer. We...

We demonstrate an efficient far-field diffraction method for quality assessment of periodically poled lithium niobate crystals. Microscopic and macroscopic analyses are carried out to obtain important statistical quantities and to assess the final device performance.

For accurate index measurement, we investigated Fabry-Perot type interference from optical wafers. Since this method is insensitive to environmental perturbation and simple to implement, it can be used to establish dispersion formula for newly developed optical materials.

We demonstrate that the nonlinear optical performance of periodically poled crystals can be exactly predicted by observing the far-field diffraction pattern. The diffraction pattern is shown to be equivalent to the second-harmonic generation tuning curve.

Periodically poled ferroelectric crystals form highly efficient quasi-phase matched optical frequency conversion devices. For optimal performance of such devices, accurate period and duty-cycle are required throughout the poled region. For the quality evaluation we demonstrate a simple and a powerful technique using far-field diffraction measuremen...

Nanocrystallized glasses with the composition of (50-x)BaO-xTiO 2-50SiO2 (x=10, 15, 16.7 and 20) have been prepared by heattreatment at Tx (crystallization onset temperature) for 3 h, and their optical properties, photoluminescence (PL), XRD and Raman spectra have been examined. The absorption edges of the glasses were red-shifted and the absorptio...

Accurate knowledge of the index of refraction of an optical medium is of fundamental importance in various optical applications. We applied a Michelson interferometer and Fabry-Perot-type interference methods to a wafer sample to estimate the difference between two orthogonal indices, Δn, of a LiNbO3 crystal wafer and we compared the results of the...

A critical angle method was used to measure the index of refraction of a solid medium when an air gap between the prism and the medium is present. The gap effect was analyzed both numerically and experimentally. Since the total internal reflection is severely disturbed by the large gap, determination of the critical angle and the resulting refracti...

We demonstrated a simple way of evaluating the duty cycle error in periodically polled lithium niobate(PPLN) based on the method of binary phase diffraction grating. To demonstrate this method, -Z face etched PPLN of desired periods were fabricated by the standard electric field poling technique. The etched PPLN was considered as a surface-relief b...

Collinear broadband optical parametric generation (OPG) using periodically poled lithium niobate (PPLN) crystals were designed and experimentally demonstrated with the quasi-phase matching (QPM) periods of 21.5, 24.0, and 27.0µm. The broad gain bandwidth was accomplished by choosing a specific set of the period and the pump wavelength that allows t...

We report ultra-broad optical parametric gain spectra centered at near infrared in periodically poled congruent LiNbO3and stoichiometric LiTaO3crystals, using group-velocity matching near the degeneracy point. They can be useful for ultrafast pulse applications.

We report on efficient collinear optical parametric generation (OPG) with gain band ranging from 1400 to 2600 nm in a 2 cm-long periodically poled lithium niobate (PPLN) crystal. Such an ultra-broad gain band was obtained by choosing the pump wavelength at 933 nm, at which the group-velocities of the signal and the idler match near the degeneracy p...

We demonstrated simultaneous red, green, and blue light generation in periodically-poled lithium niobate crystals pumped with a single picosecond laser. The blue light was obtained by multiple-order quasi-phase-matched (QPM) second-harmonic generation of the near-infrared pump input. The other colors resulted from cascaded QPM sum-frequency generat...

We present a method to estimate birefringence of wafer-type materials by using Michelson interferometry. The difference between the ordinary and extraordinary refractive indices of a LiNbO3wafer was determined to an accuracy of 10-3.

Simultaneous red, green and blue lights were generated from periodically poled lithium niobate pumped with single picosecond laser. This process was realized by a broadband design of the optical parametric generation of participating infrared frequencies.

Amplified spontaneous emission (ASE) associated with excited-state intramolecular proton transfer (ESIPT) was investigated in a single crystal and a glass of acetic acid 2-{4-[2-(2-hydroxy-phenyl)-4,5-diphenyl-imidazole-1-yl]-phenyl}-ethyl ester molecules. The polarization-dependent ASE was analyzed in an effort to understand the structural evoluti...

We observed simultaneous red, green and blue light generated from periodically poled lithium niobate pumped with single picosecond laser. This process could be realized by a broadband design of the optical parametric generation of participating infrared frequencies. Pumping wavelength, pulse width, and quasi-phase-matching period were important par...

We present a method to measure the index of refraction of a wafer-type material accurately by using a modified Michelson interferometer. With this method, the difference between the refractive index of the ordinary-wave and that of the extraordinary-wave in the representative nonlinear crystal, LiNbO3 could be measured with ease.

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.

Optical gain measurements with femtosecond excitation were performed in CdSe colloidal quantum dots (QDs) dissolved in toluene using the variable stripe length method. Instead of ZnS-shell overcoating, we found that the spectral narrowing and intensity enhancement of the fluorescence can be achieved alternatively by excluding octadecene (ODE) at th...

Transient optical gain studies have been carried out in a high-quality organic single crystal, acetic acid 2-{4-[2-(2-hydroxy-phenyl)-4,5-diphenyl- imidazole-1-yl]-phenyl}-ethyl ester (HPI-Ac), by using the variable-stripe- length method. Amplified spontaneous emission (ASE) was investigated in the HPI-Ac crystal with 35-ps laser pulses at 355 nm u...

A strong blue (460 nm) upconverted fluorescence was observed in an organic single crystal com-posed of excited-state intramolecular proton transfer molecules with pumping wavelength range from 485 to 687 nm. We deduced the two-photon absorption (TPA) spectrum by measuring the upconverted fluorescence with varying pump wavelength. The TPA spectrum r...

We demonstrate broadband optical parametric generation in the telecommunication band and the associated simultaneous RGB generation by quasi-phase-matched parametric conversion processes in a periodically poled lithium niobate crystal pumped by picosecond pulses.

Photo-induced refractive index change was investigated in organic single crystals with excited-state intramolecular protontransfer molecules. The relaxation dynamics associated with the keto-enol transition could be monitored by pump-probe method.

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-vel...

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.

We report broadband optical parametric amplification in a single periodically poled LiNbO₃ crystal pumped by a 35 ps pulse at a fixed wavelength of 870 nm.

Non-collinear second-harmonic generation (SHG) was performed using a beta-barium-borate crystal, aiming at real-time imaging through a scattering medium. In the present experiment, we successfully obtained a high resolution real-time image of the second-harmonic beam. Detailed analyses are given for the thickness of the nonlinear crystal and our re...