193-nm Laser Research Articles

Calibration and characterization of optical and x-ray streak cameras using a Ti:Sapphire laser system.

Optical and x-ray streak cameras are used to study transient phenomena, particularly in the high-energy density physics regime. The Orion laser facility employs many different types of streak cameras, which are used to collect data on laser-plasma interactions as well as to verify the temporal profile and timing between the multiple Orion beamlines. Streak cameras are complex devices with very precise timing associated with them, which can often malfunction, resulting in the loss of shot data. Since Orion is a kJ-class Nd:glass laser system, it is not optimal to try and fault-find using Orion shots since this is both time consuming and prohibitively expensive. To enable the facile set-up, fault-finding, timing-in, and in-house calibration of Orion optical and x-ray diagnostics, a single laboratory system has been commissioned to provide an adjustable stimulus to streak cameras and other Orion short pulse diagnostics (such as pulse dilation photomultiplier tubes). The system comprises a Ti:Sapphire laser system capable of generating 400nm or 266nm laser pulses of duration less than 0.1ps; an optical system to deliver single pulses, pulse pairs, or a train of pulses; and timing electronics to synchronize the streak cameras with the laser and to record output data. The system can operate at Hertz repetition rates rather than the sub-mHz rate of the Orion laser. We present the commissioned system and results from initial testing of both optical and x-ray streak cameras used on Orion laser-plasma experiments.

Elastic Organic Crystals Exhibiting Amplified Spontaneous Emission Waveguides with Standard Red Chromaticity of the Rec.2020 Gamut.

The use of mechanically flexible molecular crystals as optical transuding media is demonstrated for a plethora of applications; however, the spectral peaks of optical outputs located mainly in the range of 400-600nm are insufficient for practical telecommunication and full-color display applications. Herein, two elastically bendable organic crystals are reported that show red emission of the rec.709 gamut under 365nm UV light irradiation yet generate rec.2020 gamut red optical waveguides and amplified spontaneous emissions when irradiated by a 355nm laser. Capitalizing on the extended π-conjugation and donor-acceptor character, as well as mechanical elasticity, these organic crystals exhibit flexible optical waveguides with Commission Internationale de L'Eclairage (CIE) coordinates of (0.70, 0.29), nearly identical to the red chromaticity of the rec.2020 gamut required for ultrahigh-definition (UHD) displays. Notably, one of the elastic crystals functions as a soft resonance cavity, resulting in amplified spontaneous emission waveguides with CIE coordinates of (0.71, 0.29) and the standard red chromaticity of the rec.2020 gamut, both in straight and bent states. This study presents a new avenue for the development of high-purity red-emissive crystalline materials to create all-organic, lightweight, and mechanically compliant optical telecommunication and UHD display devices.

High efficiency LD end surface pumping quasi continuous 355nm laser

High efficiency LD end surface pumping quasi continuous 355nm laser

Performance of laser patterned copper plasmonic photocathodes

We study ultrafast laser surface nanopatterning as an alternative to improve the photo-emissive properties of metallic photocathodes. By tailoring the physical dimensions of these surface nanostructures, one can localize the optical field intensity and exploit plasmonic effects occurring in such nanostructures. As a result, this surface nanopatterning technique can become a great tool for improving metallic photocathodes photoemission behavior enabling their use for next generation high brightness electron sources. Our goal is to investigate such surface-plasmon assisted photoemission processes with a view on simplifying the photocathode production at CERN while extending the lifetime of existing photoinjectors. The performance of two different femtosecond laser nanopatterned plasmonic photocathodes was analyzed by measuring the quantum yield with a 65kV DC electron gun utilizing 266nm laser excitation generated by a nanosecond laser with 5ns pulse duration and 10Hz repetition rate. By comparing the electron emission of the copper surface nanostructured areas with that of a flat area, our results suggest quantum yield enhancements of up to a factor of 5.

Manipulating nonsequential double ionization of atoms by parallel polarized three-color laser fields

Nonsequential double ionization (NSDI) of He atoms in a parallel polarized three-color field is investigated by using a three-dimensional classical ensemble model. The driving field is composed of 1600-nm and 800-nm laser pulses with equal intensity. A weak 400-nm laser pulse is used as a controlling field. The results indicate that in the correlated electron momentum distribution and ion momentum distribution, the electron pairs and ions of the first returning recollision (FRR) trajectory, the odd-returning recollision (ORR) trajectory (excluding FRR), and the even-returning recollision (ERR) trajectory are located in different regions separated well from each other. The electron pairs from FRR trajectories mainly distribute around the origin, and those electron pairs from ORR and ERR trajectories respectively cluster in the first quadrant and the third quadrant. With the increase of the phase of the controlling field, the proportion of FRR trajectories in NSDI first increases and then decreases, and the proportions of those trajectories with the returning number more than one first decrease and then increase, which leads to the fact that with the increase of the phase of the controlling field, the anticorrelated emissions first increase and then decrease and correspondingly the ion momentum distribution evolves from a double-hump to a triple-hump and then to a double-hump structure. Moreover, NSDI from multiple-returning recollision trajectories mainly occur through recollision-induced direct ionization (RDI) mechanism, while NSDI from the FRR trajectories mainly occurs through recollision-induced excitation with subsequent ionization (RESI) mechanism. Thus the dominant NSDI ionization mechanism can also be controlled by changing the phase of the controlling field.

Fabrication and Electrical Characterization of GaAs/GaN Junctions

GaAs/GaN heterojunctions are likely to be an ideal platform for high-frequency/high-output-power electron devices because of excellent electrical properties of GaAs and GaN as well as the similarity in their coefficients of thermal expansion. We have to note, however, that heteroepitaxial growth of GaAs/GaN junctions is quite difficult because of difference in crystal structures (in case of GaAs/wurtzite GaN junctions) and large mismatch in lattice constants (GaAs/zincblende GaN junctions). In this work we fabricate p+-GaAs/n-GaN heterojunctions by bonding GaAs and GaN epi wafers to each other using surface-activated-bonding technologies [1,2], selectively etching off the GaAs substrate used in the epitaxial growth, making ohmic contacts on the exposed surface of GaAs layer, and forming GaAs mesas. Ohmic contacts on the backside of GaN epi wafer are formed before bonding. The junctions are annealed at 400 ℃ in contact formation on GaAs surfaces. The temperature is much lower in comparison with the temperature in a wafer-fusion process of GaAs and GaN (750 ℃), which were reportedly applied for fabricating group-III arsenide/nitride heterojunction bipolar transistors [3]. Observation using cross sectional transmission electron microscope (TEM) of as-bonded and 400-℃ annealed GaAs/GaN interfaces shows that no voids are formed at the GaN/GaAs interfaces by the 400-℃ annealing. We also fabricate n+-GaAs/n-GaN heterojunctions for comparison.We measure the capacitance-voltage characteristics and current-voltage characteristics for reverse-bias voltages of the p+-GaAs/n-GaN and n+-GaAs/n-GaN junctions and find that the characteristics of the two junctions are close to each other, which suggests that the band profiles of GaN layers in the p+-GaAs/n-GaN and n+-GaAs/n-GaN junctions are almost the same, i.e., the Fermi-level pinning occurs at the GaAs/GaN interfaces. More importantly, the reverse-bias characteristics are measured up to -60 V. The reverse-bias voltage corresponds to an electric field of as high as ~2 MV/cm, which is comparable to the breakdown field of GaN (3-4 MV/cm) [4]. We also excite minority electrons in the p+-GaAs layer using a 488-nm Ar laser and successfully observe the photo current due to the transport of minority electrons across the reverse-biased GaAs/GaN interfaces.Acknowledgement: TEM samples were fabricated under the Inter-University Cooperative Research in IMR of Tohoku University. Epi wafers used in the work were provided from Sciocs (present Sumitomo Chemical) Co., Ltd.[1] H. Takagi, et al. Appl. Phys. Lett. 68, 2222 (1996). [2] S. Yamajo, et al., Jpn. J. Appl. Phys. 57, 02BE02 (2018). [3] C. Lian, et al. Appl. Phys. Lett. 91, 063502 (2007). [4] T. Maeda, et al., IEEE Electron Device Lett., 43, 96 (2022).

Observation of laser ablation of silicon as a function of pulse length at constant fluence via time-resolved x-ray spectroscopy

We investigate the ablation of silicon as a function of laser pulse length at a constant fluence using time-resolved x-ray spectroscopy data obtained from OMEGA EP experiments at the University of Rochester's Laboratory for Laser Energetics. Our targets consisted of three-layer planar structures composed of Si (50 μm), Cu (25 μm), and SiO2 (500 μm) layers. The Si layer was irradiated by a 351-nm laser with varying pulse widths of 250 ps, 500 ps, 1 ns, and 10 ns while maintaining a constant fluence of ∼27.9 kJ/cm2. Electron temperatures and densities of the ablated plasma were determined by analyzing the time-resolved x-ray spectroscopy data through a comparison of experimental measurements with synthetic results obtained from Si atomic calculations in a steady state and non-local thermodynamic equilibrium. These calculations were computed using PrismSPECT [MacFarlane et al., High Energy Density Phys. 3, 181 (2007)]. Additionally, radiation-hydrodynamics simulations with FLASH are used to generate simulated plasma-density and plasma-temperature profiles, which are then compared with the experimental measurements. Our analyses reveal that increasing the laser pulse length at a constant fluence results in a decrease in electron temperatures and densities. Furthermore, the longer pulses with lower intensities lead to deeper ablation regions before reaching the peak ablation but lower ionization balances in the silicon layer. These findings emphasize the critical role of laser pulse length in plasma ablation and shock generation for laser-impulse studies.

A modified model for laser-cornea interaction following the ablation effect in the laser eye-surgery

BackgroundLaser corneal reshaping is a successful treatment of many refraction disorders. However, some physical demonstrations for the laser interaction with cornea are not fully explained. In the current paper, we present a modified model to precisely investigate the ablation threshold, the ablation rate and the physical/chemical mechanisms in that action.ResultsThe model discusses the possible photochemical reaction between the incident photons and various components of the cornea. Such photochemical reaction may end by photo-ablation or just molecular electronic excitation. The ablation threshold is also produced by other chemical reaction. Finally another chemical reaction creates out-site fragments. Moreover, the effect of applying different laser wavelengths, namely the common excimer-laser (193-nm), and the solid-state lasers (213-nm & 266-nm) has been investigated.ConclusionDespite the success and ubiquity of the Argon Fluoride “ArF” laser, our results reveal that a carefully designed 213-nm laser gives the same outcomes with the potential of possible lower operational drawbacks related with heat generation and diffusion.

Numerical Aperture-Dependent Spatial Scaling of Plasma Channels in HPHT Diamond

The investigation of plasma channels induced by focused ultra-short 1030-nm laser pulses in bulk of synthetic High Pressure High Temperature (HPHT) diamond revealed strong dependence of their spatial parameters on the used numerical aperture of the lens (NA = 0.15–0.45). It was shown that at weak focusing conditions it is possible to significantly increase the length of the plasma channel with a slight increase in pulse power, while tight focusing allows one to obtain more compact structures in the same range of used powers. Such a dependence paves the way to new possibilities in 3D processing of transparent dielectrics, allowing one, for example, to vary the spatial parameters of modified regions without changing the setup, but only by controlling the lens aperture, which seems very promising for industrial applications.

Ultraviolet photodissociation and collision-induced dissociation for qualitative/quantitative analysis of low molecular weight compounds by liquid chromatography-mass spectrometry

Collision-induced dissociation (CID) is the most wildly used fragmentation technique for qualitative and quantitative determination of low molecular weight compounds (LMWC). Ultraviolet photodissociation (UVPD) has been mainly investigated for the analysis of peptides and lipids while only in a limited way for LMWC. A triple quadrupole linear ion trap instrument has been modified to allow ultraviolet photodissociation (UVPD) in the end of the q2 region enabling various workflows with and without data-dependent acquisition (DDA) combining CID and UVPD in the same LC–MS analysis. The performance of UVPD, with a 266-nm laser, is compared to CID for a mix of 90 molecules from different classes of LMWC including peptides, pesticides, pharmaceuticals, metabolites, and drugs of abuse. These two activation methods offer complementary fragments as well as common fragments with similar sensitivities for most analytes investigated. The versatility of UVPD and CID is also demonstrated for quantitative analysis in human plasma of bosentan and its desmethyl metabolite, used as model analytes. Different background signals are observed for both fragmentation methods as well as unique fragments which opens the possibility of developing a selective quantitative assay with improved sample throughput, in particular for analytes present in different matrices.Graphical

Fabrication and Electrical Characterization of GaAs/GaN Junctions

We fabricate p+-GaAs/n-GaN and n+-GaAs/n-GaN junctions using surface activate bonding and measure their capacitance-voltage and current-voltage characteristics. We find that the characteristics of the two junctions are close to each other, which suggests that the band profiles of GaN layers in the two types of junctions are almost the same, i.e., the Fermi-level pinning occurs at the GaAs/GaN interfaces. Breakdown occurs at a reverse bias voltage ≈ -60 V in both junctions. The observed breakdown voltage corresponds to an electric field of as high as ~ 1.6 MV/cm, which is comparable to a reported breakdown field of GaN. We also excite minority electrons in the p+-GaAs layer using a 488-nm laser and successfully observe the photocurrent due to the transport of minority electrons across the reverse-biased GaAs/GaN interfaces.

Optical levitation in high vacuum using a 0.9-numerical-aperture lens

Nanoparticles levitated in high vacuum are isolated from the surrounding environment and thus can be used in various applications, including quantum physics research. We demonstrated optical levitation of a nanoparticle, which was trapped without cooling at a pressure of 4.5 × 10−3 Pa, using a single aspheric lens with a large numerical aperture (= 0.9) and 1030-nm laser. We also activated parametric feedback cooling to trap the particle at a pressure of 5.8 × 10−4 Pa. This experimental system will be useful for studying nanoparticles in ultrahigh vacuum and for building a mixed system with laser-cooled atoms.

Experimental development of a gated UV-induced spectroscopic lidar for the daytime study of plant ecology and photosynthesis: multi-modal measurement of fluorescence of trees growing in a field and Mie-Raman-fluorescence of the surrounding atmosphere.

A gated UV-induced spectroscopic lidar operational during daylight was developed to better understand the plant growth status in real time and the influence from the surrounding atmosphere chemical environment. Initial indoor experiments and short-range (100m) field measurements were very positive. The lidar worked as a vegetation fluorescence lidar, as well as an atmospheric Mie-Raman-fluorescence lidar. A UV (355nm) laser was effective to induce fluorescence and Raman scattering, and a synchronous detection technique made it possible to detect weak signals, even in daytime. Tree spectra containing chlorophyll fluorescence of tree leaves offered information about the growth status of trees. Atmospheric spectra containing aerosol Mie scattering, N 2, O 2, H 2 O Raman scattering, and pollutant fluorescence helped us to learn about atmospheric circumstances surrounding trees. The multi-modal information is useful for comprehensive understanding of plant ecology.

Comparison of high average-power femtosecond green and ultraviolet laser emissions generated by K3B6O10Br and K3B6O10Cl nonlinear crystals

We investigate the second harmonic generation (SHG) and third harmonic generation (THG) processes of femtosecond (fs) laser that occurred in type Ⅰ phase-matched K3B6O10X (X = Cl, Br; KBOC and KBOB) crystals. The high average power of 515 nm green and 343 nm ultraviolet (UV) fs lasers output were efficiently generated from these two crystals with an incident fundamental 773 fs 1030-nm laser source. Experimental results show that the highly effective nonlinear coefficient of the KBOC crystal causes higher harmonic conversion efficiency than that of KBOB crystal in the same fundamental laser parameters. The average power of 10.4 W 515 nm green and 4.6 W 343 nm UV lasers output were obtained from two pieces of 4.5 mm KBOC crystals, corresponding to 42.3 % and 19.7 % high optical conversion efficiency respectively, without temporal pulse walk-off time compensation between 1030 nm and 515 nm laser pulses. Our research will stimulate in-depth research on nonlinear frequency conversion in nonlinear optical systems and have potential applications in future applications.

Evaluating the efficacy of Nd:YAG fourth harmonic (266 nm) in comparison with ArF excimer (193 nm) in laser corneal reshaping: ex vivo pilot study

PurposeLaser corneal reshaping is a common eye surgery utilized to overcome many vision disorders. Different UV laser wavelengths can be effective in the treatment. However, the ArF excimer laser (193 nm) is the most commonly used due to its high absorption in the cornea. In the current study, we investigate the efficacy of applying a solid-state laser (Nd:YAG fourth harmonic at 266 nm) for the corneal reshaping procedure. MethodsThe utilized laser is generated using an optical setup based on a BBO nonlinear crystal which converts the Q-switched laser (532 nm) to its fourth harmonic (266 nm). Different pulse energies were applied with the same number of the shoots on ex vivo rabbit corneas, and the histological effect is studied. Moreover, the possible thermal damage on the treated corneal tissues was inspected via electron microscope. Additionally, the DNA damage on the corneal cells due to the application of the proposed laser was examined and compared with the existing technology (ArF Excimer laser at 193 nm) using the comet assay. ResultsThe histological examination revealed an appropriate ablation result with the minimum thermal effect at 1.5 mJ and 2.0 mJ. The overall results show that applying 50-shoots of the 1.5-mJ pulse energy using the proposed 266-nm solid-state laser produces the optimum ablation effect with the minimum thermal damage, and almost the same DNA damage occurred using the commercial 193-nm ArF excimer laser. ConclusionSolid-state laser at 266 nm could be a good alternative to the common 193-nm excimer laser for corneal reshaping procedures.

Experiment-based channel characteristics for underwater wireless optical communication over medium-and-long distance

We provide an experimental study of the channel characteristics in an underwater wireless optical communication (UWOC) system given by a 35-m transmission distance in various water types. A UWOC system using a low-power 488-nm laser diode is established to comprehensively evaluate the influence of the link distance, water turbidity, receiver parameters, and link misalignment on the communication link power. The results show that the link misalignment-induced power loss is significant and the effect of receiver parameters on power is limited. However, a higher turbidity or longer signal transmission distance can help to reduce the link misalignment effect and manifest the receiver parameters effect on the received power. In particular, in turbid waters with an attenuation coefficient of 0.471 m − 1, the change of the signal reception power curve is small over a certain degree of the link misalignment in the 35-m physical distance, and the reasonable configuration of receiver parameters effectively improves the signal reception quality in the UWOC system. These results can provide theoretical guidance for optimizing the UWOC system.

Evaluation of 213-nm laser as an affordable alternative for the green elemental characterization of particulate matter on quartz fibre filters by laser ablation ICPMS

Evaluation of 213-nm laser as an affordable alternative for the green elemental characterization of particulate matter on quartz fibre filters by laser ablation ICPMS

Multiphoton Ionization Reduction of Atoms in Two-Color Femtosecond Laser Fields.

We report the ionization reduction of atoms in two-color femtosecond laser fields in this joint theoretical-experimental study. For the multiphoton ionization of atoms using a 400nm laser pulse, the ionization probability is reduced if another relatively weak 800nm laser pulse is overlapped. Such ionization reduction consistently occurs regardless of the relative phase between the two pulses. The time-dependent Schrödinger equation simulation results indicate that with the assisted 800nm photons the electron can be launched to Rydberg states with large angular quantum numbers, which stand off the nuclei and thus are hard to be freed in the multiphoton regime. This mechanism works for hydrogen, helium, and probably some other atoms if two-color laser fields are properly tuned.

In-situ temperature and major species measurements of sooting flames based on short-gated spontaneous Raman scattering

Spontaneous Raman scattering is a conventional in-situ laser-diagnostic method that has been widely used for measurements of temperature and major species. However, utilization of Raman scattering in sooting flames suffers from strong interference including laser-induced fluorescence, laser-induced incandescence, and flame luminosity, which has been a challenge for a long time. This work introduces an easy-to-implement and calibration-free Raman scattering thermometry in sooting flames based on a 355-nm nanosecond-pulsed laser beam. Several strategies were utilized to increase the signal-to-noise ratio and suppress the interference: (1) nanosecond intensified CCD gate width; (2) optimized intensified CCD gate delay; (3) specially designed focused laser beam; (4) ultraviolet polarizer filter. The temperature was obtained by fitting the spectral profile of Stokes-Raman scattering of N2 molecules without any calibrations. Based on the measured temperature, the mole fraction of major species can be evaluated. This method was applied to measure the temperature and major species profiles in a steady ethylene–air counterflow diffusion flame with a spatial resolution of 1.2 mm × 10.8 mm × 0.13 mm. The experimental results agree well with the simulation results in both sooting and non-sooting regions, demonstrating the feasibility of this method for quantitative diagnostics of temperature and major species in multiphase reacting flows.

Broadband and ultrafast terahertz modulation with GeTe thin films

Chalcogenide phase change materials (PCMs) are gaining much interest for optoelectronic applications because of their capability to perform nonvolatile phase transition between the amorphous and crystalline states under Joule heat generated by applied electrical bias or optical excitation. Utilizing the high dielectric tunability of PCMs, we experimentally demonstrated the terahertz (THz) modulation with germanium telluride (GeTe) thin films. With THz time-domain spectroscopy (THz-TDS), we showed that the transmission of the 250-nm GeTe film can be tuned from 95% (amorphous) to 35% (crystallized) in the range of 0.1–1.2 THz. The high optical contrast of the GeTe film was also confirmed by Fourier transform infrared spectrometer and scattering-type scanning near-field optical microscope at higher frequencies. Ultrafast time-resolved optical pump–THz probe experiments were performed with 400-nm laser pulses. The amorphous and crystalline phases of GeTe exhibit different volatile THz modulation capabilities on the picosecond time scale and their decay times are 1.39 ps and 0.73 ps, respectively.