A quasi-continuous-wave deep ultraviolet laser source

The realization of new ultraviolet laser sources and the improvement of existing laser sources require new optical components with more and more severe requirements. Three examples will be considered here: solid-state ultraviolet (UV) laser sources, excimer laser sources and free electron laser (FEL) sources. In the first case, dichroic mirror with high steepness between high reflecting and high transmitting wavelength range are required, to make UV tunable sources. In the second case, the use of graded mirrors in the laser cavity allows an improvement of the laser beam quality. In the third case optical coatings able to withstand the synchrotron radiation are needed. The required performance for optical coatings to be used in this kind of laser sources are described, and critical points underlined.

Ambient pressure photoemission spectroscopy of metal surfaces

We report on a 183-MW, 1-kHz, 9-ps, 1.65-mJ deep ultraviolet laser at 257.25 nm based on a frequency-quadrupled, cryogenic Yb:YAG chirped-pulse amplifier and an overall nonlinear conversion efficiency of ~5%, scalable to ~25%.

We review the physics of deep UV LEDs with emphasis on the features that differ from those for visible LEDs. We discuss UV designs, novel growth process of light generating structures (MEMOCVD^TM) that allows for reducing the growth temperature and improving materials quality, and "phonon engineering" approach that takes advantage of high polar optical energy in AlN/GaN/InN materials for confining electrons in the light emitting quantum wells. We then review the characteristics of DUV LEDs grown on sapphire substrates with peak emission wavelength from 250 to 340 nm that demonstrate the lowest optical noise among all other UV light sources and, therefore, are well suited for the detection of hazardous biological agents using fluorescence techniques. Finally, we describe high power multi-chip, multi-wavelength deep UV light sources and review emerging applications of deep UV LED technology.

Linearly polarized wavelength stable single frequency ytterbium (Yb³⁺) doped fiber lasers below 1 μm, namely threelevel Yb³⁺ fiber lasers, are highly demanded for nonlinear wavelength conversion to generate coherent blue light or even deep ultraviolet coherent sources. We present performance of a 976 nm single-frequency core-pumped distributed Bragg reflector (DBR) fiber laser consisting of a 2-cm long highly ytterbium-doped phosphate fiber and a pair of silica fiber Bragg gratings (FBGs) and their use for frequency doubling experiment. The high reflection (HR > 99%) and partial reflection (PR = 60%) FBGs were cleaved very close to the index modulation region and directly spliced to a 2-cm-long highly Yb³⁺-doped phosphate fiber. Over 100 mW of linearly polarized output with a linewidth less than 2 kHz can be obtained when the launched pump power is about 450 mW. The efficiency of the 976 nm single-frequency fiber laser (the output power vs the launched pump power) is about 25%. The relative intensity noise was measured to be -110 dB/Hz at 1 MHz and the variation of the center wavelength is less than 0.0005 nm during a measurement period of 2.5 hours. This single-frequency fiber laser has an SNR of over 50 dB and there is no strong ASE or spurious lasing at long wavelengths even at the maximum pump power. This all-fiber single-frequency DBR laser with attractive features can be used for efficient blue and UV generation through nonlinear frequency conversion. Moreover, this high-performance 976 nm single-frequency fiber laser can be used as a single-frequency, low RIN pump laser for long wavelength Yb³⁺-, Er³⁺-, or Yb³⁺/Er³⁺-doped fiber lasers and amplifiers.

There is an increasing need for narrow linewidth, high average power ultraviolet (UV) laser sources for high resolution spectroscopy, remote environmental sensing, laser-induced fluorescence, semiconductor inspection, and LIDAR applications [1,2]. A way to design efficient sources in the UV is to frequency convert diode-pumped solid-state lasers that emit in the near infrared (IR) [3]. In this case, obtaining high nonlinear conversion efficiency requires a large peak power in the fundamental wave. At a fixed repetition rate and average power, this results in a tradeoff between attainable linewidth, related to the pulse duration, and the nonlinear conversion efficiency.

Discrimination of stem cells with flow cytometric analysis of Hoechst 33342 efflux by the ABCG2 transporter (termed the Hoechst side population, or SP technique) is a valuable methodology for identifying bone marrow progenitors enriched with stem cells. Unfortunately, it requires a ultraviolet (UV) laser source, usually necessitating an expensive and maintenance-intensive argon- or krypton-ion gas laser on a large-scale cell sorter. In this study, we evaluated the ability of recently available violet and near-UV laser diodes to discriminate Hoechst SP on smaller cuvette-based flow cytometers. Violet laser diodes (emitting at 408 and 401 nm) and a near-UV laser diode (emitting at 370 nm) were mounted on a BD Biosciences LSR II and evaluated for their ability to discriminate Hoechst SP in murine bone marrow. The violet laser diodes discriminated the Hoechst SP, but with poorer resolution than with the standard UV gas laser on a large-scale cell sorter. The near-UV laser diode, in contrast, gave excellent Hoechst SP resolution. These evaluations indicated that near-UV laser diodes give excellent Hoechst SP resolution on cuvette-based instruments. As the next generation of cell sorters integrate cuvette-based cell interrogation into conventional jet-in-air cell separation, these laser sources should become applicable for analysis and physical separation of Hoechst SP cells.

Sub-wavelength printing in the deep ultra-violet region using Displacement Talbot Lithography

Photodissociation of ozone following absorption of biologically harmful solar ultraviolet radiation is the key mechanism for the life protecting properties of the atmospheric ozone layer. Even though ozone photolysis is described successfully by post-Hartree-Fock theory, it has evaded direct experimental access so far, due to the unavailability of intense ultrashort deep ultraviolet radiation sources. The rapidity of ozone photolysis with predicted values of a few tens of femtoseconds renders both ultrashort pump and probe pulses indispensable to capture this manifestation of ultrafast chemistry. Here, we present the observation of femtosecond time-scale electronic and nuclear dynamics of ozone triggered by \ensuremath{\sim}10-fs, \ensuremath{\sim}2-\textmu{}J deep ultraviolet pulses and, in contrast to conventional attochemistry experiments, probed by extreme ultraviolet isolated pulses. An electronic wave packet is first created. We follow the splitting of the excited B-state related nuclear wave packet into a path leading to molecular fragmentation and an oscillating path, revolving around the Franck-Condon point with 22-fs wave-packet revival time. Full quantum-mechanical ab initio multiconfigurational time-dependent Hartree simulations support this interpretation.

This paper describes the design and construction of the automatic calibration unit (ACU) for the JUNO experiment. The ACU is a fully automated mechanical system. It is capable of deploying multiple radioactive sources, an ultraviolet (UV) laser source, or an auxiliary sensor such as a temperature sensor, one at a time, into the central detector of JUNO along the central axis. It is designed as a primary tool to precisely calibrate the energy scale of detector, aligning timing for the photosensors, and partially monitoring the position-dependent energy scale variations.

Mass spectrometry using matrix-assisted laser desorption/ionization (MALDI) technique is one of the most widely used method to analyze proteins in biological research fields. However, it is difficult to analyze insoluble proteins which have important roles in researches on disease mechanisms or in developments of drugs by using ultraviolet (UV) lasers which have commonly been used for MALDI. Recently, a significant improvement in MALDI process of insoluble proteins using a combination of a UV nitrogen laser and a tunable mid-infrared (MIR) free electron laser (FEL) was reported. Since the FEL is a very large and expensive equipment, we have developed a tabletop laser source which can generate both UV and tunable MIR lasers. A tunable MIR laser (5.5–10 µm) was obtained by difference frequency generation (DFG) between a Nd:YAG and a tunable Cr:forsterite lasers using two AgGaS 2 crystals. The MIR laser can generate pulses with an energy of up to 1.4 mJ at a repetition rate of 10 Hz. A UV laser was obtained by third harmonic generation of a Nd:YAG laser splitted from that used for DFG. A time interval between the UV and the MIR laser pulses can be adjusted with a variable optical delay. Keywords: difference frequency generation, tunable mid-infrared laser, third harmonic generation, mass spectrometry, matrix-assisted laser desorption/ionization

In this study, we employed a newly built time-slice velocity-map ion imaging setup, equipped with two tunable vacuum ultraviolet (VUV) laser sources, to obtain the first comprehensive high-resolution photoexcitation and photofragment excitation spectra of 14N15N in the VUV photon energy range 109 000-117 500cm-1. The spectroscopic simulation program PGOPHER was used to analyze the rotationally resolved spectra. Band origins, rotational constants, and isotope shifts compared with those of 14N2 have been obtained for 31 electric-dipole-allowed vibrational states of 14N15N in the aforementioned energy range. These spectroscopic parameters are found to depend on the vibrational quantum number irregularly. Systematic perturbations of the rotational transition energies and predissociation rates within individual absorption bands have also been observed. These are proved to be caused by the strong homogeneous interactions between the valence b'1Σu + state and the Rydberg cn ' 1Σu + states, and between the valence b1Πu states and the Rydberg o3 1Πu states. Heterogeneous interactions between the Rydberg cn 1Πu states and cn ' 1Σu + states also play an important role.

A scanning Raman lidar for observing the spatio-temporal distribution of water vapor

Multimode silica step-index optical fibers are examined for use in planar laser-induced fluorescence (PLIF) for combustion diagnostics using ultraviolet (UV) laser sources. The multimode step-index fibers are characterized at UV wavelengths by examining their energy damage thresholds and solarization performance. The beam quality achievable with large clad step-index multimode fibers is also studied. Emphasis is placed on simultaneously achieving high output energy and beam quality (low output M(2)). The use of multimode fibers to deliver UV pulses at 283 nm for PLIF measurements of OH radicals in a Hencken burner is demonstrated. The fiber delivery capability of UV light will benefit combustion diagnostics in hostile environments, such as augmentor and combustor rigs.

Compact, reliable, and cost-efficient ultraviolet (UV) laser sources are attractive for many applications including radiometric characterization of detectors in the biologically interesting solar UV band 300-320 nm.