Deep Ultraviolet Laser Research Articles

Polarization control proposal for Shanghai deep ultraviolet free electron laser

In this paper, a fully coherent radiation option with controllable polarization is proposed for the Shanghai deep ultraviolet free electron laser (FEL) test facility. Intensive start-to-end simulation suggests that the two crossed planar undulators which generate the horizontal and vertical linear polarized FEL, should be placed as close as possible for avoiding the polarization performance degradation of the final combined FEL radiation. With the existence of the phase-shifter between the two crossed radiators, Fourier-Transform-Limited output radiation with 100nJ order pulse energy, 5ps full pulse length and circular polarization degree above 90% could be achieved.

Calibration of 25-nm Pitch Grating Reference by X-ray Diffraction

We have developed grazing incidence x-ray diffraction pitch calibration system with wavelength of 0.1540593 nm (Cu Kα1 line). In order to ensure consistency of this calibration system with currently used deep ultra violet (DUV) laser diffraction pitch calibration system, we measured average pitch of a 100-nm pitch grating reference for CD-SEM. The average pitch determined by the x-ray diffraction agreed with that determined by the DUV laser diffraction within the range of expanded uncertainty. We measured average pitch of a next generation 25-nm pitch grating for which DUV laser no longer works. We have successfully detected more than ten sharp diffraction peaks corresponding to the 25-nm period. The average pitch of the grating was measured in high-accuracy with expanded uncertainty of 40 pm. The result agreed well with that determined by metrological atomic microscope (AFM) within the range of expanded uncertainty.

Efficient continuous wave deep ultraviolet Pr3+:LiYF4 laser at 261.3 nm

We report continuous wave deep ultraviolet laser operation at 261.3 nm by intracavity frequency doubling of laser diode pumped Pr3+ doped LiYF4 lasers. Using two InGaN laser diodes with a maximum output power of about 1 W each, a 2.9 mm long Pr3+:LiYF4 crystal and a 5 mm long beta-barium-borate crystal, coherent radiation with an output power of 481 mW at 261.3 nm was achieved at an optical-to-optical efficiency of 26.1% with respect to the total pump power. Both, linear and nonlinear losses have been calculated to be approximately 0.6% by using a model for intracavity frequency doubling with focussed Gaussian beams.

Deep UV laser etching of GaN epilayers grown on sapphire substrate

The laser etching of GaN epilayers on sapphire substrate was carried out using a deep ultraviolet pulsed laser (157 nm wavelength, 20 ns pulse width). The quality and morphology of the etched GaN surface were evaluated by scanning electron microscopy, atomic force microscopy and scanning profilometer. Quadrate micro-hole and micro-trenches etched by the 157 nm laser exhibited clean and smooth edges, sharp side walls and very small heat affected zone (HAZ). In order to achieve controllable high-quality etching, the laser and processing parameters, such as laser repetition rate, scan speed, were systematically investigated and optimized. The mechanism analysis shows that, direct photoionization or photo-chemical reaction play predominant role within 157 nm laser etching of GaN epilayers.

Two-color deep-ultraviolet 40-fs pulses based on parametric amplification at 100 kHz

We present a 100-kHz deep-ultraviolet (DUV) laser system that generates 40-fs pulses. A 520-nm pulse generated by a noncollinear optical parametric amplifier pumped by the second harmonic of a Ti:sapphire laser is converted into 226- and 260-nm DUV pulses simultaneously with pulse energies of 250 and 130 nJ (average powers: 25 and 13 mW), respectively. The DUV pulses were estimated to have durations of ca. 40 fs by cross-correlation measurements based on (1 + 1') two-color ionization of gaseous nitric oxide.

Towards a monolithic fiber laser with deep UV femtosecond-induced fiber Bragg gratings

Fiber Bragg grating inscription with a deep ultraviolet (DUV) femtosecond laser and two-beam interferometry allows grating inscription in germanium-free fibers without classical UV photosensitivity. Therefore such a writing technology is a promising solution for the fabrication of fiber Bragg gratings in the active fiber material to realize a fully integrated all-fiber solution. In this paper we report on the use of the DUV femtosecond laser fiber Bragg grating technology to build a grating-stabilized fiber laser with high spectral purity. Output powers up to 158 W at 1083 nm and a slope efficiency of 76% have been demonstrated.

Differential laser-induced perturbation spectroscopy using a deep-ultraviolet excimer laser

Here we demonstrate a unique optical sensing scheme based on deep-UV photochemical perturbation in combination with difference spectroscopy. Applying a sequence of optical probing, UV-laser-induced perturbation, and repeat optical probing coupled with difference spectroscopy provides a new spectral signature. We show a selective (sevenfold difference) optical response using a fluorescence probe for binary mixtures of organic dyes, and generate complementary spectral information derived from Raman scattering of the dipeptide glycine-glycine. We further extend the methodology to fluorescence-based imaging of an organic matrix.

Large optical gain AlGaN-delta-GaN quantum wells laser active regions in mid- and deep-ultraviolet spectral regimes

The gain characteristics of high Al-content AlGaN-delta-GaN quantum wells (QWs) are investigated for mid- and deep-ultraviolet (UV) lasers. The insertion of an ultrathin GaN layer in high Al-content AlGaN QWs leads to valence subbands rearrangement, which in turn results in large optical gain for mid- and deep-UV lasers.

Impact of strain on deep ultraviolet nitride laser and light-emitting diodes

To date, the shortest wavelength of an ultraviolet current-injection nitride laser has been limited to ∼340 nm. This begs the question of whether there is a fundamental limitation that restricts the realization of injection lasers below this wavelength. This letter investigates this issue. We find that, apart from being the decisive factor for the crystalline quality of nitride epitaxial layers, residual strain plays yet another crucial role in modifying the band structure of (Al,Ga)N quantum wells. A critical analysis of quantum-confinement effects, strain, and the polarization properties of strained (Al,Ga)N layers is essential for the realization of deep ultraviolet laser diodes.

A permanent optical storage medium exhibiting ultrahigh contrast, superior stability, and a broad working wavelength regime

In this paper we demonstrate an optical storage medium having advantages of ultrahigh contrast, superior stability, and broadband working wavelengths. Combining a single shot of deep-ultraviolet (UV) laser illumination with a Au particle-assisted etching process, we formed broadband antireflective, one-dimensional silicon nanowire arrays (SiNWs) with selectively at specific positions. Optical measurements and three-dimensional finite-difference time domain (3D-FDTD) simulations revealed ultrahigh reflection contrast between the Au and the SiNWs for both far- and near-field regimes. Relative to typical organic-based storage media, Au films and SiNWs are more stable, both chemically and thermally; therefore, we suspect that this new storage medium would exhibit high stability toward moisture, sunshine, and elevated temperatures.

Multi-reflected enhancement of fourth harmonic DUV laser generation at 266 nm

The stable compact operation in the deep ultraviolet laser at 266 nm is reported from a diode-end-pumped acoustic-optic Q-switched Nd:YVO4/KTP/BBO laser. Fourth harmonic is generated by employing multiple reflections of 532 nm light for taking full advantage of the green beam. An ultraviolet laser at 266 nm with average power of 388.5 mW is obtained with a repetition-rate of 20 kHz, a pulse width of about 59.80 ns, and the corresponding optical to optical conversion efficiency of 11.9% from green to UV. High conversion efficiency and a circular spot of 266 nm laser beam have been achieved in an unfocused beam arrangement.

A proposed method to characterize high harmonic microbunching in EEHG operation of SDUV-FEL

The echo-enabled harmonic generation (EEHG) scheme offers remarkable efficiency for generating high harmonic microbunching with a relatively small energy modulation. A proof of principle experiment of the EEHG scheme has been proposed at the Shanghai deep ultraviolet (SDUV) free electron laser (FEL) facility, where the 4th harmonic of the seed laser is amplified in the 9 m long radiator. To explore the advantages of the EEHG scheme, in this paper, a method of measuring the coherent high harmonic radiation of the radiator is proposed to investigate the electron beam microbunching corresponding to the 10th-20th harmonics of the seed laser. The principle of the proposed method, comparisons with existing methods and the simulation results are presented and discussed.

Deep UV Raman Spectroscopy of Epitaxial Graphenes on Vicinal 6H-SiC Substrates

We report microscopic Raman scattering studies of epitaxial graphene grown on SiC substrates using a deep-ultraviolet (UV) laser excitation at 266 nm to elucidate the interaction between the graphene layer and the substrate. The samples were grown on the Si-face of vicinal 6H-SiC (0001) substrates by sublimation of Si from SiC. The G band of the epitaxial graphene layer was clearly observed without any data manipulation. Increasing the number of graphene layers, the peak frequency of the G-band decreases linearly, while the peak width and the intensity increase. The G-band frequency of the graphene layers on SiC is higher than those of exfoliated graphene, which has been ascribed to compression from the substrate.

Anti-Reflective Fluoride Coatings for Widely Tunable Deep-Ultraviolet Diode-Pumped Solid-State Laser Applications

An anti-reflective (AR) fluoride coating in the 170–230 nm spectral range is prepared by the thermal evaporation method for the applications of widely tunable deep-ultraviolet diode-pumped solid-state lasers. The transmittance of an AR coated calcium fluoride (CaF2) window in thickness 3 mm is measured to be in the range of 95.8% at 170 nm to 97.1% at 230 nm, with the maximum transmittance 99.2% and the minimum residual reflectance 0.04% appeared at 195 nm. The experimental results indicate that treating the AR coated window and the bare substrate with ultraviolet irradiation can significantly improve their optical performance.

Three dimensional study of harmonic operation at the Shanghai deep ultraviolet free electron laser

With the right choice of parameters in the free electron laser (FEL) scheme, the undulator can be primarily operated at high order harmonic modes and the harmonic radiation is expected to be significantly enhanced. Recently, the possibility of proof-of-principle harmonic operation experiments on the basis of the Shanghai deep ultraviolet (SDUV) FEL test facility has been studied. In this paper, the principle of harmonic operation, three dimensional numerical approaches, and detailed performances of proposed harmonic operation at SDUV FEL are presented.

One-Shot Deep-UV Pulsed-Laser-Induced Photomodification of Hollow Metal Nanoparticles for High-Density Data Storage on Flexible Substrates

In this paper, we report a new optical data storage method: photomodification of hollow gold nanoparticle (HGN) monolayers induced by one-shot deep-ultraviolet (DUV) KrF laser recording. As far as we are aware, this study is the first to apply HGNs in optical data storage and also the first to use a recording light source for the metal nanoparticles (NPs) that is not a surface plasmon resonance (SPR) wavelength. The short wavelength of the recording DUV laser improved the optical resolution dramatically. We prepared HGNs exhibiting two absorbance regions: an SPR peak in the near-infrared (NIR) region and an intrinsic material extinction in the DUV region. A single pulse from a KrF laser heated the HGNs and transformed them from hollow structures to smaller solid spheres. This change in morphology for the HGNs was accompanied by a significant blue shift of the SPR peak. Employing this approach, we demonstrated its patterning ability with a resolving power of a half-micrometer (using a phase mask) and developed a readout method (using a blue-ray laser microscope). Moreover, we prepared large-area, uniform patterns of monolayer HGNs on various substrates (glass slides, silicon wafers, flexible plates). If this spectral recording technique could be applied onto thin flexible tapes, the recorded data density would increase significantly relative to that of current rigid discs (e.g., compact discs).

41mW high average power picosecond 177.3nm laser by second-harmonic generation in KBBF

Abstract We report on the generation of high average power, high repetition rate, and picosecond (ps) deep-ultraviolet (DUV) 177.3 nm laser. The DUV laser is produced by second-harmonic generation of a frequency-tripled mode-locked Nd: YVO4 laser (

Asynchronous cross-correlation for weak ultrafast deep ultraviolet laser pulses

We have developed a technique for the temporal characterisation of weak deep-ultraviolet (DUV) ultrashort laser pulses by combining asynchronous optical sampling with difference-frequency mixing. The intensity profile of picosecond DUV pulses, with peak powers as low as 2.5 W, have been measured accurately with a resolution of 50 fs. The method can be extended to complete amplitude and phase characterisation of few femtosecond laser pulses at DUV wavelengths.

1.9 W闪光灯抽运固态266 nm紫外激光器

Deep ultraviolet lasers have various applications in industries and scientific researches. For 266-nm ultraviolet (UV) laser generation, the good beam quality of 1064-nm laser and the elimination of gray-tracking effect of KTP crystal are two key factors. Using a dynamically stable resonator design, 1064-nm laser with an average power of 52 W is realized with repetition rate of 16 kHz. The measured M2 factor characterizing the beam quality is 1.5. By the elimination of gray-tracking effect of KTP crystal, an 18-W green laser is realized with the M2 factor of 1.6. Using a BBO crystal for the fourth harmonic generation, a 1.9-W 266-nm UV laser is achieved.

Plasma channel formed by ultraviolet laser pulses at 193 nm in air

The propagation of picosecond deep ultraviolet laser pulse at wavelength of 193 nm in air is numerically investigated. Long plasma channel can be formed due to the competition between Kerr self-focusing and ionization induced defocusing. The plasma channel with electron density of above 10lsupg13l/supg/cmlsupg3l/supg can be formed over 70 m by 50-ps, 20-mJ laser pulses. The fluctuation of laser intensity and electron density inside ultraviolet (UV) plasma channel is significantly lower than that of infrared pulse. The linear absorption of UV laser by air is considered in the simulation and it is shown that the linear absorption is important for the limit of the length of plasma channel.