Deep Ultraviolet Laser Research Articles

Photoreactions of Porphyrins Initiated by Deep Ultraviolet Single Photons.

The newly built 177 nm all-solid-state deep ultraviolet (DUV) laser photoionization mass spectrometer finds a unique advantage to identify porphyrins that bear ionization energies close to 7.0 eV. We observed dramatic selectivity of tetraphenylporphyrins (TPPs) pertaining to varied photochemical processes initiated by the DUV laser excitation. Single-photon ionization was found dominant for 2H-TPP resulting in a fragmentation-free mass spectrum; photoinduced dehydrogenation was observed for zinc TPP, but both dehydrogenation and demetalation are noted for copper TPP. Along with first-principle calculations, we demonstrate how the photoinduced reactions vary with residual energies of photoionization, highest occupied molecular orbital-lowest unoccupied molecular orbital gaps, donor-acceptor orbital overlaps, single-step barriers, and whether or not there is a major process of structural rearrangement. It is demonstrated that the rotation of benzene ring under proper laser radiation prompts dehydrogenation process; also, metallo-TPPs do not support direct demetalation, but it is selectively accomplishable along with dehydrogenation and successive hydrogenation processes. These findings not only provide insights into the hydrogen atom transfer in porphyrins initiated by ultraviolet laser but also suggest promising applications of the DUV laser in designed synthesis and chemical modification of porphyrins.

Electrically driven deep ultraviolet MgZnO lasers at room temperature

Semiconductor lasers in the deep ultraviolet (UV) range have numerous potential applications ranging from water purification and medical diagnosis to high-density data storage and flexible displays. Nevertheless, very little success was achieved in the realization of electrically driven deep UV semiconductor lasers to date. In this paper, we report the fabrication and characterization of deep UV MgZnO semiconductor lasers. These lasers are operated with continuous current mode at room temperature and the shortest wavelength reaches 284 nm. The wide bandgap MgZnO thin films with various Mg mole fractions were grown on c-sapphire substrate using radio-frequency plasma assisted molecular beam epitaxy. Metal-semiconductor-metal (MSM) random laser devices were fabricated using lithography and metallization processes. Besides the demonstration of scalable emission wavelength, very low threshold current densities of 29~33 A/cm2 are achieved. Numerical modeling reveals that impact ionization process is responsible for the generation of hole carriers in the MgZnO MSM devices. The interaction of electrons and holes leads to radiative excitonic recombination and subsequent coherent random lasing.

Biodegradability of poly(lactic-co-glycolic acid) and poly(l-lactic acid) after deep-ultraviolet femtosecond and nanosecond laser irradiation

In this study, we investigated the change in biodegradability of biodegradable polymer films by deep-ultraviolet laser irradiation with different pulse durations. Measurements of water absorption and mass change as well as microscopic observation revealed that the femtosecond laser irradiation significantly accelerated the degradation rate of the biodegradable polymer films, whereas the nanosecond laser irradiation did not induce a comparable degree of change. Analyses with X-ray photoelectron spectroscopy and X-ray diffraction indicate that the difference in the biodegradability following laser irradiation with different pulse durations is attributable to the difference in chemical structure for amorphous polymers including PLGA, while the difference in chemical structure as well as crystallinity affects the biodegradability for crystalline polymer including PLLA. The obtained results suggest that deep-ultraviolet laser processing enables the fabrication of a tissue scaffold with a desirable degradation rate.

Beam test results of high Q CBPM prototype for SXFEL

In pursuit of high-precision beam position measurements at micrometers or submicrometers for the Shanghai soft X-ray free-electron laser (SXFEL) facility which is under construction in the vicinity of the Shanghai Synchrotron Radiation Facility, a high Q cavity beam position monitor (CBPM) with a resonant frequency of 4.7 GHz is developed by the Shanghai Institute of Applied Physics, and the relevant BPM electronics with a dedicated RF front end, and a digital BPM, are completed. The cavity design, cold test, system architecture, and first beam test are performed at the Shanghai deep ultraviolet free-electron laser (Zhao et al. in Nucl Instrum Meth A 528(1–2):591–594, 2004. doi: 10.1016/j.nima.2004.04.108 ) facility. Results of the beam experiment show that the performance of the CBPM is consistent with basic expectations, and the beam position resolution can fulfill the requirements for the SXFEL project if the beam conditions are optimized.

Optical investigation of semi-polar (11-22) AlxGa1-xN with high Al composition

Exciton localization generally disturbs uniform population inversion, leading to an increase in the threshold current for lasing. High Al content AlGaN is required for the fabrication of deep ultra-violet (DUV) laser diodes (LDs), and this also generates exciton localization. Temperature-dependent photoluminescence and room temperature cathodoluminescence measurements have been performed on high quality semi-polar (11-22) AlxGa1-xN alloys with high Al composition ranging from 0.37 to 0.56 in order to systematically study the optical properties (in particular, exciton localization) of both the near-band-edge emission and the basal-plane stacking faults related emission, demonstrating different behaviours. Further comparison with the exciton localization of their c-plane counterparts has been performed, exhibiting that the exciton localization in semi-polar (11-22) AlGaN is much smaller than that in c-plane AlGaN. As a consequence, semi-polar (11-22) AlGaN demonstrates a greater potential than its c-plane counterpart in terms of the growth of DUV LDs.

Applications of deep ultraviolet laser photo-and thermal-emission electron microscope in thermal dispenser cathode research

The research of micro-region emission state for thermal dispenser cathode surface,especially in-situ observation and analysis,is an important subject in the field of thermal cathode.A newly developed instrument aiming at meeting the special operation requirements of thermal dispenser cathode is used to carry out this research.This instrument combines the functions of deep ultraviolet laser photo-emission electron microscope and thermal-emission electron microscope,so it is called DUV-PEEM/TEEM.In this paper,its basic principle is introduced emphatically.In addition,the actual applications of the microscope system to the electron emission investigation of thermal dispenser cathode are displayed. This system is equipped with the heating unit,which is used for activating the thermal dispenser cathode sample,and the temperature of sample can reach 1400℃.The system has three imaging modes,namely,photoemission electron imaging, cathode thermal emission electron imaging,and united imaging by integrating cathode thermal emission electron and photoemission electron.By applying new microscope system to traditional thermal dispenser cathode,we acquire the photoemission electron images of impregnated barium aluminate cathode surface at room temperature.In the heating process,we observe the thermal electron emission phenomenon originating from thermal dispenser cathode and record the variation process with temperature change.A high emission cathode which we developed before,is also studied with DUV-PEEM/TEEM.Fortunately,we find that some bright stripes appear on the surface of high emission cathode when the cathode temperature reaches 800℃.The widths of these bright stripes are about 100 nm.We calculate the thermal emission electron imaging resolution of this system by using these thermal electron emission stripes and the obtained resolution reaches 28 nm.Conveniently,the emission performance and uniformity of this high emission cathode are compared with those of traditional impregnated barium aluminate cathode directly at same temperature. Using united imaging mode of the system,in-situ observation and analysis of thermal electron emission spots on high emission cathode surface are carried out successfully.The results indicate as follows.For thermal dispenser cathode,the deep ultraviolet laser photoemission electron imaging can be used to show the surface fundamental micro-morphology of cathode;cathode thermal emission electron imaging is suitable for revealing the intrinsic emission uniformity of the thermal dispenser cathode;with the united imaging by integrating cathode thermal emission electron and photoemission electron,the positions of effective emission points on cathode surface can be fixed accurately.Based on these applications and findings,we believe that DUV-PEEM/TEEM also has ability to investigate the processes of cathode poisoning and recovery.

A High-Power Deep-UV Picosecond Laser

Toward the development of a high-power deep-ultraviolet picosecond laser, we report the features of a tested laser system and the experimentally observed relation between the fundamental-wave light source and the thermal effects during deep-ultraviolet wavelength conversion. The laser is expected to be operational at 266 nm for about 2000 h based on lifetime tests of 300 h at an average output of 10 W, pulse width of 9.8 ps, and repetition frequency of 200 kHz.

Dispersion relations of refractive indices suitable for KBe2BO3F2 crystal deep-ultraviolet applications.

KBe2BO3F2 (KBBF) is the only nonlinear optical crystal available to generate deep-ultraviolet (DUV) laser output by direct harmonic generation. High-precision refractive indices, including in the DUV region, were measured, and starting from a double resonance model of polarizability, new dispersion relations of the refractive indices were deduced from the measured data. The predicted phase matching angles for second-harmonic generation down to 165 nm from the new relations agree well with the previous reported values. Moreover, the new dispersion relations show superior results in an even shorter wavelength range, giving perfectly calculated phase matching angles for fifth-harmonic generation down to as short as 149.8 nm.

Improved Crystalline Quality of AlN by Epitaxial Lateral Overgrowth Using Two-Phase Growth Method for Deep-Ultraviolet Stimulated Emission

We report on the maskless epitaxial lateral overgrowth (ELOG) of the AlN layer on trench-patterned AlN/sapphire templates by metal-organic chemical vapor deposition (MOCVD). With a two-phase growth of different V/III ratio at a relatively low growth temperature of 1250 °C, up to a 7.3-μm-thick high-quality crack-free AlN film with a threading dislocation density of 8 × 108 cm–2 was obtained. Compared with the 0.9-μm AlN film grown on a planar sapphire substrate, the ELOG-AlN film has a lower dislocation density and a much better strain state, regardless of its 7.3-μm thickness. Compared with the single low V/III ratio growth, the two-phase growth method can lead to a coherent coalescence at the second growth stage and hence suppress new dislocations generating at the coalescence fronts. Stimulated emission was observed from Al(Ga)N multi-quantum-wells laser grown on the ELOG-AlN template with low dislocation density. The deep-ultraviolet laser (DUV) on these templates exhibited lasing at 263.3 nm with the spectral linewidth of 1.29 nm and threshold pumping power density of 2.7 MW/cm2 at room temperature.

A Brief History of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA–ICP–MS)

Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) has been used for more than 30 years to determine the elemental composition of natural and synthesized objects. A focused laser beam ablates a small volume of target material, and the aerosol produced is transferred in a gas stream to an ICP–MS for elemental and/or isotopic analysis. Through the increasing use of deep ultraviolet lasers and ultra-sensitive mass spectrometers, the technique has evolved towards higher sampling resolution and to generating 2-D (and 3-D) images of compositional variations. The future is likely to see femtosecond lasers and simultaneous mass spectrometers in common use, making new research areas possible.

Generation of femtosecond laser pulses at 396 nm in K3B6O10Cl crystal**Project supported by the National Key Basic Research Program of China (Grant Nos. 2013CB922401 and 2013CB922402) and the National Natural Science Foundation of China (Grant Nos. 11474002, 61205130, and 61575219).

K3B6O10Cl (KBOC), a new nonlinear optical crystal, shows potential advantages for the generation of deep ultraviolet (UV) light compared with other borate crystals. In this paper we study for the first time the second harmonic generation (SHG) of a femtosecond Ti:sapphire amplifier with this crystal. Laser power is obtained to be as high as 220 mW at the central wavelength of 396 nm with a 1-mm-long crystal, and the maximum SHG conversion efficiency reaches 39.3%. The typical pulse duration is 83 fs. The results show that second harmonic (SH) conversion efficiency has the room to be further improved and that the new nonlinear crystal is very suited to generate the high efficiency deep ultraviolet laser radiation below 266 nm.

Focusing far-field nanoscale optical needles by planar nanostructured metasurfaces

Far-field nanoscale optical needles are obtained using water-immersed planar nanostructured metasurfaces illuminated with a 193nm deep ultra-violet laser. The method is based on the vectorial angular spectrum theory and an established nonlinear optimization model. For a 50μm-diameter metasurface with a linearly polarized beam (x-polarized), an optical needle with 12.4λ0 length has been produced at a mid-focal distance of 14.5μm. The transverse beam sizes are as small as 129nm and 59.4nm in the x and y directions, respectively. The design results are agreed well with the rigorous electromagnetic calculations using three-dimensional finite-difference time-domain (FDTD) method with a suggested 25nm-thick aluminum coating film for the metasurface. These far-field nanoscale optical needles are potentially applied in the fields of nanolithography, nanoprinting, and nanoscopy.

Improved beam profile of a 266 nm deep ultraviolet laser employing a multi-mirror-reflected cavity

A 266 nm deep ultraviolet (DUV) laser with a good Gaussian profile is reported employing a multi-mirror-reflected cavity. A type-I LiB3O5 (LBO) crystal is used to double the fundamental-light (1064 nm) wavelength generated by an actively Q-switched Nd:YVO4 laser with an intra-cavity configuration. A fourth harmonic generation (FHG) wavelength is obtained by a type-I β-BaB2O4 (BBO) crystal. The output power as high as 440 mW at 266 nm is generated under an incident power of 2.26 W at 532 nm, corresponding to the conversion efficiency of 532 nm–266 nm up to 19.5% with a repetition rate of 15 kHz and the pulse duration of 266 nm is 10.7 ns.

Neon shortage looms

A looming shortage of neon gas threatens to create problems for manufacturers of semiconductors and the devices they power beginning in 2017. Producers of the latest computer and cell phone chips use a laser-enabled photolithography technique to create transistors and other device features. Deep ultraviolet lasers, which contain neon gas as a buffer, have made it possible to pack an increasing number of transistors on chips that now boast features as small as 14 nm wide. Semiconductor makers had hoped to transition by this year to extreme ultraviolet lasers, which enable even smaller features but don’t require the noble gas. But delays in that technology mean the industry will continue to rely on neon-consuming lasers, “pushing up demand for neon beyond what the supply chain can support” by 2017, says Lita Shon-Roy, CEO of Techcet, a consulting firm that issued a report on the problem. Chip makers, which account for

Detection of Explosives Using Differential Laser-Induced Perturbation Spectroscopy with a Raman-based Probe.

Explosives detection is carried out with a novel spectral analysis technique referred to as differential laser-induced perturbation spectroscopy (DLIPS) on thin films of TNT, RDX, HMX, and PETN. The utility of Raman spectroscopy for detection of explosives is enhanced by inducing deep ultraviolet laser perturbation on molecular structures in combination with a differential Raman sensing scheme. Principal components analysis (PCA) is used to quantify the DLIPS method as benchmarked against a traditional Raman scattering probe, and the related photo-induced effects on the molecular structure of the targeted explosives are discussed in detail. Finally, unique detection is observed with TNT samples deposited on commonly available background substrates of nylon and polyester. Overall, the data support DLIPS as a noninvasive method that is promising for screening explosives in real-world environments and backgrounds.

All-solid-state deep ultraviolet laser for single-photon ionization mass spectrometry.

We report here the development of a reflectron time-of-flight mass spectrometer utilizing single-photon ionization based on an all-solid-state deep ultraviolet (DUV) laser system. The DUV laser was achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2 under the condition of high-purity N2 purging. The unique property of this laser system (177.3-nm wavelength, 15.5-ps pulse duration, and small pulse energy at ∼15 μJ) bears a transient low power density but a high single-photon energy up to 7 eV, allowing for ionization of chemicals, especially organic compounds free of fragmentation. Taking this advantage, we have designed both pulsed nanospray and thermal evaporation sources to form supersonic expansion molecular beams for DUV single-photon ionization mass spectrometry (DUV-SPI-MS). Several aromatic amine compounds have been tested revealing the fragmentation-free performance of the DUV-SPI-MS instrument, enabling applications to identify chemicals from an unknown mixture.

2.14 mW deep-ultraviolet laser at 165 nm by eighth-harmonic generation of a 1319 nm Nd:YAG laser in KBBF

We report a nanosecond (ns) 165 nm deep-ultraviolet (DUV) laser with a maximum average power of 2.14 mW by eighth-harmonic generation (EHG) of a homemade ns 1319 nm Nd:YAG laser. The EHG was performed by cascaded second-harmonic generation (SHG) through successive stages of two LiB3O5 crystals and one KBe2BO3F2 crystal. The generated radiation at 165 nm is the shortest DUV wavelength ever generated through SHG method and the highest average power of all solid state lasers below 170 nm to our knowledge. Such a ns DUV laser at 165 nm is of great interest for photoemission spectroscopy and Raman spectroscopy.

Ultrafast dynamics of uracil and thymine studied using a sub-10 fs deep ultraviolet laser

Single 9.6 fs deep ultraviolet pulses with a spectral range of 255-290 nm are generated by a chirped-pulse four-wave mixing technique for use as pump and probe pulses. The electronic excited state and vibrational dynamics are simultaneously observed for an aqueous solution of uracil and thymine over the full spectral range using a 128-channel lock-in amplifier detector. Two probe photon energy-dependent lifetimes gradually increasing with the probe photon energy are obtained from the decay dynamics data. Ultrafast decay dynamics through the conical intersection is assigned from the first excited ππ* to the final ground state involving the nπ* states. Vibrational modes of the electronic ground state and excited states can be observed, which are strongly coupled to the decay dynamics of the electronic excited state.

Three-Dimensional Quantum Confinement of Charge Carriers in Self-Organized AlGaN Nanowires: A Viable Route to Electrically Injected Deep Ultraviolet Lasers.

We report on the molecular beam epitaxial growth and structural characterization of self-organized AlGaN nanowire arrays on Si substrate with high luminescence efficiency emission in the deep ultraviolet (UV) wavelength range. It is found that, with increasing Al concentration, atomic-scale compositional modulations can be realized, leading to three-dimensional quantum confinement of charge carriers. By further exploiting the Anderson localization of light, we have demonstrated, for the first time, electrically injected AlGaN lasers in the deep UV band operating at room temperature. The laser operates at ∼289 nm and exhibits a threshold of 300 A/cm(2), which is significantly smaller compared to the previously reported electrically injected AlGaN multiple quantum well lasers.

Residual Stress Analysis of Indentation on 4H-SiC by Deep-Ultraviolet Excited Raman Spectroscopy

In this work, we analyze residual stress on 4H-SiC with Raman spectroscopy that excitation wavelength is deep ultraviolet (DUV) laser 266nm. The residual stress area is created by Vickers Hardness test technique and the area is measured by 2D DUV Raman map. The result is different from visible light excited Raman, because DUV light penetration is shallower than visible light. DUV Raman signal has exactly brings only the sample surface information. We present the advantage of DUV excited Raman to analyze sample surface.