Power Ultraviolet Laser Research Articles

Coherent beam combining of femtosecond third-harmonic generators: towards high-power, high-beam-quality UV light generation.

Coherent beam combining (CBC) of two femtosecond third-harmonic (TH) generators is proposed and demonstrated. By applying phase modulation to one of the fundamental laser pulses, the feedback loop effectively eliminates both phase and pointing errors between the two TH femtosecond laser beams. The system delivers 345-nm femtosecond laser pulses with 22-W average power at 1-MHz repetition rate. The average combining efficiency is 91.5% over approximately 1 h of testing. The beam quality of the combined ultraviolet (UV) laser beam is near-diffraction-limited with M2 factors of M X2=1.36, M Y2=1.24, which are similar to those of the individual channels. This scheme exhibits promising potential for increasing high-beam-quality UV laser power.

High power green picosecond laser and high efficiency ultraviolet femtosecond laser through second harmonic generation using K3B6O10Br crystal

We demonstrated high power green picosecond (ps) laser and high efficiency ultraviolet (UV) femtosecond (fs) laser through second harmonic generation (SHG) using type I phase-matched K3B6O10Br (KBOB) nonlinear optical crystals. The green ps laser was generated by using a homemade high power 1064 nm ps laser as the pump source. When the pump power was 28.2 W with a repetition rate of 800 kHz, 14.2 W ps green laser was obtained with the maximum optical conversion efficiency of 50.4%. When the pump power was 85.2 W with a repetition rate of 800 kHz, the maximum output power of 41.8 W of ps green laser was achieved with an optical conversion efficiency of 49.1%. During the UV fs laser generation, a 710 nm fs laser with a repetition rate of 1 kHz was used to pump the KBOB crystal. When the pump power of 710 nm laser was 54 mW, the 355 nm UV fs laser was obtained with output power of 18 mW and optical conversion efficiency of 33.3%. The experimental results show that the KBOB crystal is a highly qualified candidate for the application in generating high power ultrafast green and UV lasers.

Development and characterization of a 22 W narrow-linewidth 3186 nm ultraviolet laser

We demonstrate a high-power narrow-linewidth ultraviolet (UV) laser system at 318.6 nm for direct 6S1/2-nP (n = 70 to 100) Rydberg excitation of cesium atoms. Based on commercial fiber lasers and efficient nonlinear frequency conversion technology, 2.26 W of tunable UV laser power is obtained from cavity-enhanced second harmonic generation following sum-frequency generation of two infrared lasers at 1560.5 nm and 1076.9 nm to 637.2 nm. The maximum doubling efficiency is 57.3%. The typical UV laser power root-mean-square fluctuation is less than 0.87% over 30 minutes, and the continuously tunable range of the UV laser frequency is more than 6 GHz. Its beam quality factors M2 X and M2 Y are 1.16 and 1.48, respectively. This high-performance UV laser has significant potential use in quantum optics and cold atom physics.

Laser performance of the SG-III laser facility

SG-III laser facility is now the largest laser driver for inertial confinement fusion research in China. The whole laser facility can deliver 180 kJ energy and 60 TW power ultraviolet laser onto target, with power balance better than 10%. We review the laser system and introduce the SG-III laser performance here.

Injection locking of a high power ultraviolet laser diode for laser cooling of ytterbium atoms.

We developed a high-power laser system at a wavelength of 399 nm for laser cooling of ytterbium atoms with ultraviolet laser diodes. The system is composed of an external cavity laser diode providing frequency stabilized output at a power of 40 mW and another laser diode for amplifying the laser power up to 220 mW by injection locking. The systematic method for optimization of our injection locking can also be applied to high power light sources at any other wavelengths. Our system does not depend on complex nonlinear frequency-doubling and can be made compact, which will be useful for providing light sources for laser cooling experiments including transportable optical lattice clocks.

Temperature-insensitive frequency tripling for generating high-average power UV lasers

Aimed for generating high-average power ultraviolet (UV) lasers via third-harmonic generation (THG) consisting of frequency doubling and tripling stages, we numerically and experimentally demonstrate a novel frequency tripling scheme capable of supporting temperature-insensitive phase-matching (PM). Two cascaded tripling crystals, with opposite signs of the temperature derivation of phase-mismatch, are proposed and theoretically studied for improving the temperature-acceptance of PM. The proof-of-principle tripling experiment using two crystals of LBO and BBO shows that the temperature acceptance can be ~1.5 times larger than that of using a single tripling crystal. In addition, the phase shift caused by air dispersion, along with its influence on the temperature-insensitive PM, are also discussed. To illustrate the potential applications of proposed two-crystal tripling design in the high-average-power regime, full numerical simulations for the tripling process, are implemented based on the realistic crystals. The demonstrated two-crystal tripling scheme may provide a promising route to high-average-power THG in the UV region.

Numerical simulation of different aperture ICF high power ultraviolet laser propagating through a long air path

It is necessary for high power ultraviolet lasers to propagate through a long air path during experiments of inertial confinement fusion (ICF). When the product of gain efficiency and propagation distance is beyond the stimulated rotational Raman scattering (SRRS) threshold, the high power ultraviolet laser beam is subject to loss of energy and a decrease in beam quality, further resulting in the reduction of conversion efficiency of triple-harmonic, and even causing the optical components to be destroyed. This paper studies the four-dimension numerical modeling of SRRS effects, with emphasis on the variation of beam aperture and corresponding beam distributions in near field. The research showed that the variation of the pump beam aperture made little effect on SRRS transform efficiency ratio with the same incident energy and the same propagation distance, the transverse intensity distribution of beams became more even with an increase in the beam aperture. We have made the deduction that high power laser's SRRS effects through a long air path could be depressed by increasing the beam aperture on the condition of equal incident energy and propagation distance.

Application of the UV laser printing technique to soft gelatin capsules containing titanium dioxide in the shells

Aim: The purpose of this study was to examine application of ultraviolet (UV) laser irradiation to printing soft gelatin capsules containing titanium dioxide (TiO2) in the shells and to study effect of UV laser power on the color strength of printing on the soft gelatin capsules.Methods: Size 6 Oval type soft gelatin capsules of which shells contained 0.685% TiO2 and 0.005% ferric dioxide were used in this study. The capsules were irradiated pulsed UV laser at a wavelength 355 nm. The color strength of the printed capsules was determined by a spectrophotometer as total color difference (dE).Results: The soft gelatin capsules which contained TiO2 in the shells could be printed gray by the laser. Many black particles, which were associated with the printing, were formed at the colored parts of the shells. It was found that there were two inflection points in relationship between output laser energy of a pulse and dE. Below the lower point, the capsules were not printed. From the lower point to the upper point, the capsules were printed gray and total color difference of the printing increased linearly in proportion with the output laser energy. Beyond the upper point, total color difference showed saturation because of micro-bubbles formation at the laser irradiated spot.Conclusions: Soft gelatin capsules containing TiO2 in the shells could be performed stable printing using the UV laser printing technique. Color strength of the printing could be controlled by regulating the laser energy between the two inflection points.

Fabrication of Circular Periodic Structures on Polymers Using High Pulse Energy Coherent Radiation and an Axicon

AbstractFabrication of micrometer concentric ring structures on polymer substrate using an axicon and high power ultra violet laser radiation is reported. The fabrication method consists on producing a periodic intensity distribution over the polymer's surface with a Bessel beam shape. The micropatterns were fabricated using a pulsed laser system operating at either 266 or 355 nm. Theoretical calculations of the periodic intensity distribution are used to explain the observed experimental results. The simple optical arrangement used in this work can be used to fabricate the above mentioned patterns over several mm2.

Factors affecting color strength of printing on film-coated tablets by UV laser irradiation: TiO2 particle size, crystal structure, or concentration in the film, and the irradiated UV laser power

Aim: The purpose of this article is to study factors affecting color strength of printing on film-coated tablets by ultraviolet (UV) laser irradiation: particle size, crystal structure, or concentration of titanium dioxide (TiO2) in film, and irradiated UV laser power.Methods: Hydroxypropylmethylcellulose films containing 4.0% of TiO2, of which BET particle sizes were ranging from 126.1 to 219.8 nm, were irradiated 3.14 W of UV laser at a wavelength 355 nm to study effects of TiO2 particle size and crystal structure on the printing. The films containing TiO2 concentration ranging from 1.0 to 7.7% were irradiated 3.14 or 5.39 W of the UV laser to study effect of TiO2 concentration on the printing. The film containing 4.0% of TiO2, was irradiated the UV laser up to 6.42 W to study effect of the UV laser power on the printing. The color strength of the printed films was estimated by a spectrophotometer as total color difference (dE).Results: Particle size, crystal structure, and concentration of TiO2 in the films did not affect the printing. In the relationship between the irradiated UV laser power and dE, there found an inflection point (1.6 W). When the UV laser power was below 1.6 W, the films were not printed. When it was beyond the point, total color difference increased linearly in proportion with the irradiated laser power.Conclusions: The color strength of the printing on film was not changed by TiO2 particle size, crystal structure, and concentration, but could be controlled by regulating the irradiated UV laser power beyond the inflection point.

One- and Two-Step Ultraviolet and Infrared Laser Desorption Ionization Mass Spectrometry of Asphaltenes

The determination of reliable molecular-weight distributions of complex asphaltene fractions has challenged modern mass spectrometry. This investigation extends previous studies on the application in this field of one-step laser desorption/ionization (LDI) and two-step laser desorption/post-ionization (L2MS) techniques employing ultraviolet (UV) and mid-infrared (IR) wavelengths. In the LDI experiments, single-resonant UV (280 nm) or IR (3.45 μm) laser pulses are applied for desorption−ionization of a model asphaltene sample. In the L2MS approach, asphaltene neutrals are postionized in the gas phase by a high power UV (266 nm) laser pulse. The study confirms that one-step UV−LDI easily induces aggregation of the asphaltenes. In contrast, in one-step IR−LDI and two-step UV/UV−L2MS and IR/UV−L2MS, aggregation is largely suppressed and the measurements reproduce correctly the known molecular-weight distribution of the model asphaltenes, with a bulk of constituents within m/z 200−1000. It is shown that the tw...

New ultraviolet lasers for material processing in industrial applications

Ultraviolet (UV) lasers are in many ways ideal industrial processing tools. They offer a noncontact method of producing fine microstructures on many substances, with minimal effect on surrounding material. The most important type of high power UV laser for industrial applications is the excimer laser. Available wavelengths include 351, 308, 248, 193, and 157 nm. The largest commercially available excimer lasers generate up to 200 W stabilized average power and up to 700 mJ pulse energy at 308 nm. Nd:yttrium aluminum garnet (YAG) lasers that utilize nonlinear crystals to transform the 1.06 μm output to its third (355 nm), fourth (266 nm), or fifth (213 nm) harmonic are also an important industrial UV source. More and more diode-pumped, frequency multiplied Nd:YAG lasers greatly impact the industrial processing market. The advantage of this laser is that it is physically compact, highly reliable, and mechanically rugged. Coupled with advantages of short wavelength output, recent improvements in laser reliability, cost of ownership, and performance are enabling UV lasers to be employed in an expanding range of applications. This article will briefly review those applications and their main laser requirements, and then present the most current advances in UV laser technology which address those needs.

Raman shifting of KrF laser radiation for tropospheric ozone measurements

The differential absorption lidar (DIAL) measurement of tropospheric ozone requires use of high average power ultraviolet lasers operating at two appropriate DIAL wavelengths. Laboratory experiments have demonstrated that a KrF excimer laser can be used to generate several wavelengths with good energy conversion efficiencies by stimulated Raman shifting using hydrogen (H2) and deuterium (D(2)). Computer simulations for an airborne lidar have shown that these laser emissions can be used for the pecise (less than 5% random error) high resolution (200-m vertical, 3-km horizontal) measurement of ozone across the troposphere using the DIAL technique. In the region of strong ozone absorption, laser wavelengths of 277.0 and 291.7 nm were generated using H(2) and D(2), respectively. In addition, a laser wavelength at 302.0 nm was generated using two cells in series, with the first containing D(2) and the second containing H(2). The energy conversion efficiency for each wavelength was between 14 and 27%.

A comparison of low‐power helium‐cadmium and argon ultraviolet lasers in commercial flow cytometers

The feasibility of installing a low power ultraviolet (UV) laser in a commercial flow cytometer was evaluated by testing an Ortho Cytofluorograf 50HH and a Coulter Epics V. Both instruments were equipped with two argon ion lasers, one emitting at 488 nm and the other in the UV region and were tested by measuring the DNA content of cells stained with Hoechst 33342 or DAPI. The coefficient of variation (CV) of the G0/G1 peak of the DNA histograms produced by each instrument did not deteriorate markedly when results obtained at 100-125 mW were compared to those obtained at 10 mW. These tests indicated that a helium-cadmium laser (He-Cd) which can produce 10 mW at 325 nm should work well as a UV laser in these instruments. An Ortho Cytofluorograf IIs was purchased with a 10 mW He-Cd laser installed in the forward position. Studies of DNA content have confirmed that this low power UV laser can produce CVs of 2.2% with DAPI stained fixed cells and 3.6% with Hoechst 33342 stained viable lymphocytes. Thus, the He-Cd laser should provide a reasonable alternative as a UV source for flow cytometers.

Photofragment Fluorescence Following Ultraviolet Laser Multiphoton Excitation

Molecular multiphoton excitation with high power ultraviolet lasers allows access to highly excited states which may undergo fragmentation to produce a variety of interesting excited-state products. Recent work on photo-fragment fluorescence following excimer laser photolysis of various small molecules is reviewed, and aspects related to the mechanisms of excitation and fragmentation and various practical implications are discussed.

Photochemistry with high power ultraviolet lasers

Rotationally resolved photofragment fluorescence from OH(A2Σ+) following the coherent two-photon excitation of H2O with a KrF laser (248 nm), is reported and the dynamics of the dissociation process are discussed. Fluorescence from CN(B2Σ+) following two-photon excitation of ICN is also described. In both cases the energy distribution in the photofragments is shown to differ significantly from that observed with single-photon excitation at closely similar energies.Two further examples of multiphoton excitation, involving CS2 and SO2, are briefly discussed. In these cases absorption of a further photon, by fragments produced in the primary step, gives rise to strong laser-induced fluorescence.