Deep Ultraviolet Laser Research Articles

A Nd-doped silica glass with high doping concentration, low hydroxyl content, and 900 nm fluorescence emission fabricated by laser additive manufacturing

The 900 nm wavelength laser is effective for atmospheric detection and various other applications.The frequency-doubled 450 nm deep blue laser can be used in maritime military, quantum optics, biomedicine, laser storage, laser display, and deep ultraviolet laser fields, among others. Although Nd3+ is considered the optimal medium for generating 900 nm lasers, competition with the 1060 nm emission wavelength must be addressed. In Nd-doped silica glass, without the introduction of aluminum, the emission intensity of the three-level transition is higher than that of the four-level transition. However, it can cause a concentration quenching between Nd3+, but co-doping with Al can effectively suppress it. As the Al/Nd ratio increases, the emission intensity at 1060 nm increases relative to that at 900 nm. By precisely adjusting the Al/Nd ratio, it is possible to suppress the 1060 nm emission while also inhibiting concentration quenching caused by Nd3+.

Deep ultraviolet laser at 223.8 nm with adjustable repetition rate and narrow pulse width.

We presented the first, to our knowledge, demonstration of an ultraviolet (UV) laser at 223.8 nm by six-harmonic generation of an electro-optic Q-switched cavity dumping 1342 nm Nd:YVO4 laser. It offers high power, constant short pulse duration, and adjustable pulse repetition rate. The pulse duration is independent of the pump power and repetition rate compared to classical Q-switched oscillators. The output efficiency of the UV laser is optimized by adjusting the focusing lens. With the incident pump power of 30 W, an maximum average output power of 249 mW was obtained at 13 kHz. The pulse width maintained 3.4-3.5 ns from 5 to 20 kHz. The maximum pulse energy of 28.1 µJ was obtained at 5 kHz, and the corresponding peak power was up to 8.1 kW.

Investigation on the performance of deep ultraviolet edge emitting laser diodes using graded undoped AlGaN electron blocking layer (EBL)

P-AlGaN EBLs are usually used to control the overflow of electrons from the multiple quantum wells (MQWs) in AlGaN-based deep ultraviolet (DUV) edge-emitting laser diodes (EELDs). They're specially designed to prevent the excess flow of electrons from the MQW. This control is essential for maintaining the laser's efficiency and performance. Using optimized parameters of Al composition through theoretical calculations using Crosslight software helps certify the electrically driven EELD functions effectively within the desired operational range. In this study, the traditional p-AlGaN EBL within the electrically driven EELD is substituted with an undoped AlGaN EBL. This modification aims to raise the effective barrier height of the conduction band, and thus effectively stopping the electron leakage while improving the injection of holes. By optimizing the aluminum composition in the current research, efforts are made to lower the threshold current (Ith) and elevate the overall enactment of the graded undoped AlGaN EBL EELD. Various structural designs, including both conventional and undoped configurations, have been successfully created and analyzed in this study. Particular attention was given to investigating the impact of grading techniques applied to the electron-blocking layer. The graded undoped AlGaN EBL EELD performed better than the highly doped AlGaN EBL EELD due to the minimized free carrier absorption loss. Specifically, it shows higher slope efficiency (S.E) of 1.45 W/A and a significantly lower Ith of 790 mA. A new AlGaN EBL EELD design was tested with different layers. The ones with a graded undoped EBLs performed better than traditional AlGaN EBL EELD, improving power efficiency. The graded undoped EBLs setup also reduced the threshold current compared to traditional AlGaN EBL EELD.

High-power, narrow linewidth solid-state deep ultraviolet laser generation at 193 nm by frequency mixing in LBO crystals

High-power, narrow linewidth solid-state deep ultraviolet laser generation at 193 nm by frequency mixing in LBO crystals

Tailoring Titanium Carbide Clusters for New Materials: from Met-Cars to Carbon-Doped Superatoms.

Tailoring materials with prescribed properties and regular structures is a critical and challenging research topic. Early transition metals were found to form supermagic M8C12 metallocarbohedrenes (Met-Cars); however, stable metal carbides are not limited to this common stoichiometry. Utilizing self-developed deep-ultraviolet laser ionization mass spectrometry, here, we report a strategy to generate new titanium carbides by reacting pure Tin clusters with acetylene. Interestingly, two products corresponding to Ti17C2 and Ti19C10 exhibit superior abundances in addition to the Ti8C12 Met-Cars. Using global-minimum search, the structures of Ti17C2 and Ti19C10 are determined to be an ellipsoidal D4d and a rod-shaped D5h geometry, respectively, both with carbon-capped Ti4C moieties and superatomic features. We illustrate the electronic structures and bonding nature in these carbon-doped superatoms concerning their enhanced stability and local aromaticity, shedding light on a new class of metal-carbide nanomaterials with atomic precision.

Developing Deep Ultraviolet Laser Diode: Design and Improvement of Al0.62Ga0.38N/Al0.68Ga0.32N Quantum Wells on AlN Substrates for 266 nm DUV Emission

A deep ultraviolet (DUV) laser diode is a compact and efficient semiconductor device that emits laser light in the deep ultraviolet range. Its unique properties make it suitable for a wide range of applications in fields such as manufacturing, research, and healthcare. In this research we propose two Al-graded Electron Blocking Layer (EBL) and quantum barriers (QBs) to improve the performance of AlGaN-based Deep UV-LDs. The electrical properties and optical properties of three structures containing conventional EBL, composition graded increased EBL, and liner graded increased of EBL and QBs were numerically investigated. It was found that the structure-C with linear graded increased EBL and QBs significantly improved the Optical Confinement Factor (OCF) 21%, gain 1600 cm-1, emission power 0.060 W, raised the carrier concentration in the MQWs region, enhanced the stimulated recombination rate and reduced the carrier leakage, of the laser diode (LDs). But at a 100-mA injection current, the threshold current and voltage were reduced to 43 mA and 5.00 V, valance barrier height 270 meV respectively. In compare to the conventional structure, introducing a graded design for both EBL and Quantum Barriers (QBs) with increased aluminum content significantly enhanced the performance of the laser diode (LD). This improvement is essential for advancing Deep Ultraviolet Laser Diodes (DUV-LD) technology.

Laser-induced voltage of table salt for deep ultraviolet pulsed laser detection

To meet the requirements of fast response and simple process of deep ultraviolet (UV) pulsed laser detector, table salt (TS) was used as laser detection material in combination with a variable resistor to achieve single-pulse laser detection. Under the irradiation of a KrF excimer laser, the laser-induced voltage (LIV) of TS was influenced by the dynamic process of laser-induced plasma, and the whole process was well fitted with the sum of the three exponential functions. As the applied bias voltage (Vb) and incident laser energy (Ein) increased, the LIV amplitude (Vp) increased and the response time decreased. When the variable resistor (R)was reduced to 14.7Ω, the response time of LIV decreased from ∼300μs to ∼20ns, which is the same as the duration of laser pulse. This research provided a simple, low-cost, and fast method for the detection of UV single-pulse laser based on the laser-TS interaction.

All-light communication network for space-air-sea integrated interconnection.

Space-air-sea communication networks are of great interest to meet the demand for close and seamless connections between space, land, and ocean environments. Wireless light communication can expand network coverage from land to the sky and even the ocean while offering enhanced anti-interference capabilities. Here, we propose and establish an all-light communication network (ALCN) for space-air-sea integrated interconnection, which merges underwater blue light communication, wireless white light communication, solar-blind deep ultraviolet light communication and laser diode-based space communication. Ethernet switches and the Transmission Control Protocol are used for space-air-sea light interconnection. Experimental results show that the ALCN supports wired and wireless device access simultaneously. Bidirectional data transmission between network nodes is demonstrated, with a maximum packet loss ratio of 5.80% and a transmission delay below 74 ms. The proposed ALCN provides a promising scheme for future space-air-sea interconnections towards multiterminal, multiservice applications.

Improving fourth harmonic generation performance by elevating the operation temperature of ADP crystal.

In current inertial confinement fusion (ICF) facilities, potassium dihydrogen phosphate (KH2PO4, KDP) type crystals are the only nonlinear optical (NLO) materials that can satisfy the aperture requirement of the ICF laser driver. Ammonium dihydrogen phosphate (NH4H2PO4, ADP) crystal is a typical isomer of KDP crystal, with a large nonlinear optical coefficient, high ultraviolet transmittance, and large growth sizes, which is an important deep ultraviolet (UV) NLO material. In this paper, we investigated the effect of ADP temperature on its fourth-harmonic-generation (FHG) performance. When the temperature of the ADP crystal was elevated to 48.9 °C, the 90° phase-matched FHG of the 1064 nm laser was realized. Compared with the 79° phase-matched FHG at room temperature (23.0 °C), the output energy at 266 nm, conversion efficiency, angular acceptance, and laser-induced damage threshold (LIDT) increased 113%, 71%, 623%, 19.6%, respectively. It shows that elevating ADP temperature is an efficient method to improve its deep UV frequency conversion properties, which may also be available to other NLO crystals. This discovery provides a very valuable technology for the future development of UV, deep UV lasers in ICF facilities.

Low-threshold AlGaN-based deep ultraviolet laser enabled by a nanoporous cladding layer.

We demonstrated an AlGaN-based multiple-quantum-well (MQW) deep ultraviolet (DUV) laser at 278 nm using a nanoporous (NP) n-AlGaN as the bottom cladding layer grown on the sapphire substrate. The laser has a very-low-threshold optically pumped power density of 79 kW/cm2 at room temperature and a transverse electric (TE)-polarization-dominant emission. The high optical confinement factor of 9.12% benefiting from the low refractive index of the nanoporous n-AlGaN is the key to enable a low-threshold lasing. The I-V electrical measurement demonstrates that an ohmic contact can be still achieved in the NP n-AlGaN with a larger but acceptable resistance, which indicates it is compatible with electrically driven laser devices. Our work provides insights into the design and fabrication of low-threshold lasers emitting in the DUV regime.

Impact of unintentionally formed compositionally graded layer on carrier injection efficiency in AlGaN-based deep-ultraviolet laser diodes

Increasing the injection efficiency, a critical factor constraining the reduction in threshold current in AlGaN-based deep-ultraviolet laser diodes, represents one of the paramount remaining technical challenges. In this study, the impact of compositionally graded layers that were unintentionally formed at the interface between the p-cladding and the core layer on carrier injection efficiency was analyzed. Experimental evaluations using laser diodes have shown that the elimination of an unintentionally formed layer increases the injection efficiency above the threshold current, from the conventional 3% to 13%. It has been postulated that the electron overflow toward the p-side exerts a substantial deleterious effect on the injection efficiency. An improvement in this aspect is achieved by increasing the electron-blocking capability due to the improved interface abruptness between the p-cladding layer and the core layer. The lasing threshold was strongly reduced, and characteristic temperature increased from 76 to 107 K for the improved devices.

Effect of optimized quaternary waveguides on the performance of deep ultraviolet laser diodes

Efficient ultraviolet (UV) laser diodes (LD) emitting in the 260–270 nm range have been proposed numerically in this work. Using engineered quaternary waveguides (QWGs) in place of conventional ternary waveguides, in the p-region, results in much higher output power as well as internal quantum efficiency (IQE) and lower the lasing threshold. The electron outflow is reduced and the injection of holes is enhanced which results in high efficiency and high light power output.

Enhanced production of <sup>199</sup>Hg cold atoms based on two-dimensional magneto-optical trap

Efficient preparation of cold atoms plays an important role in realizing precision measurement including optical lattice clocks (OLCs). Fast preparation of cold atoms reduces Dick noise by shortening dead time in a clock interrogation cycle, which improves the stability of OLCs. Here, we increase the loading rate of the three-dimensional magneto-optical trap (3D-MOT) in the ultra-high vacuum environment by utilizing the two-dimensional magneto-optical trap (2D-MOT) with a push beam, reduce the temperature of cold atoms with the compression-MOT technique which is implemented by reducing the detuning of 3D-MOT rapidly at the end of atom preparation, and realize the enhanced production of cold atoms for <sup>199</sup>Hg OLCs. To achieve 3D-MOT and 2D-MOT of mercury atoms, a deep ultraviolet laser (DUVL) system composed of three DUVLs is developed with one working in lower power for frequency locking and the other two in high power for laser cooling. Such a configuration improves the long-term frequency stability and shows greater robustness than our previous system consisting of two DUVLs. To maximize the 3D-MOT loading rate, we orderly optimize the detuning and the magnetic field gradient of 3D-MOT and those of 2D-MOT as well as the detuning and the power of the push beam. After all parameters are optimized, we measure the maximum loading rate of 3D-MOT to be 3.1×10<sup>5</sup> s<sup>–1</sup> and prepare cold atoms of 1.8×10<sup>6</sup> in 9 s. The loading rate is greatly enhanced by a factor of 51 by using 2D-MOT and the push beam. In order to improve the efficiency of transferring cold atoms from 3D-MOT to optical lattice, we use compression-MOT technique to reduce the temperature of cold atoms and produce cold <sup>199</sup>Hg atoms which are about 45 μK, lower than the expected temperature of Doppler cooling theory. By achieving the high gain of the 3D-MOT loading rate under the ultra-high vacuum and reducing the temperature of cold atoms, this enhanced preparation of cold atoms based on 2D-MOT effectively shortens the preparation time of cold atoms and improves the transfer efficiency of optical lattice, which provides a significant scheme for efficiently preparing cold mercury atoms in other experiments.

Angularly Cascaded Long-Period Fiber Grating for Curvature and Temperature Detection.

A high-sensitivity curvature sensor with dual-parameter measurement ability based on angularly cascaded long-period fiber grating (AC-LPFG) is proposed and experimentally demonstrated, which consists of two titled LPFGs (TLPFGs) with different tilt angles and the same grating period. AC-LPFG was fabricated by using a deep ultraviolet laser and an amplitude-mask in our laboratory. The experimental results show that simultaneous measurement of curvature and temperature can be achieved by monitoring the wavelengths of two resonant peaks for different TLPFGs. The two peaks show opposite shifts with increasing curvature and has a maximum curvature sensitivity of 16.392 nm/m-1. With the advantages of low cost, high sensitivity, and dual-parameter measurements, our sensor has more potential for engineering applications.

7.56-W continuous-wave Pr3+-based green laser via managing thermally induced effects.

Blue-laser-diode-pumped Pr3+-based continuous-wave (CW) green lasers have aroused growing research interest in developing optoelectronic applications and deep ultraviolet laser sources due to their simple and compact structural design. However, the obstacle of thermally induced effects limits the available output power of Pr3+-based green lasers. Herein, combined with the theoretical analysis and experimental feedback, we effectively adjust the heat distribution inside the Pr3+:LiYF4 gain crystal by optimizing the crystal dimension and doping concentration. The excellent mode matching between the pump and green lasers is achieved under the consideration of thermally induced effects, yielding a maximum CW output power of 7.56 W. To the best of our knowledge, this is the largest output power of Pr3+-based CW green lasers so far. Moreover, the obtained green laser demonstrates excellent output stability (RMS = 1.27%) and beam quality (M2 = 1.30 × 1.12) under the lasing operation state with the maximum output power. We hope that this study can provide a feasible paradigm for developing blue-laser-diode-pumped visible lasers, especially for high-power lasers.

Deep ultraviolet 266 nm laser excitation for flow cytometry.

High dimensional flow cytometry relies on multiple laser sources to excite the wide variety of fluorochromes now available for immunophenotyping. Ultraviolet lasers (usually solid state 355 nm) are a critical part of this as they excite the BD Horizon™ Brilliant Ultraviolet (BUV) series of polymer fluorochromes. The BUV dyes have increased the number of simultaneous fluorochromes available for practical high-dimensional analysis to greater than 40 for spectral cytometry. Immunologists are now seeking to increase this number, requiring both novel fluorochromes and additional laser wavelengths. A laser in the deep ultraviolet (DUV) range (from ca. 260 to 320 nm) has been proposed as an additional excitation source, driven by the on-going development of additional polymer dyes with DUV excitation. DUV lasers emitting at 280 and 320 nm have been previously validated for flow cytometry but have encountered practical difficulties both in probe excitation behavior and in availability. In this article, we validate an even shorter DUV 266 nm laser source for flow cytometry. This DUV laser provided minimal excitation of the BUV dyes (a desirable characteristic for high-dimensional analysis) while demonstrating excellent excitation of quantum nanoparticles (Qdots) serving as surrogate fluorochromes for as yet undeveloped DUV excited dyes. DUV 266 nm excitation may therefore be a viable candidate for expanding high-dimensional flow cytometry into the DUV range and providing an additional incidental excitation wavelength for spectral cytometry. Excitation in a spectral region with strong absorption by nucleic acids and proteins (260-280 nm) did result in strong autofluorescence requiring care in fluorochrome selection. DUV excitation of endogenous molecules may nevertheless have additional utility for label-free analysis applications.

Development of Room Temperature Continuous-Wave Deep Ultraviolet Laser Diodes

Development of Room Temperature Continuous-Wave Deep Ultraviolet Laser Diodes

Evaluating the performance of an AlGaN based deep ultraviolet laser diode using graded waveguide layer and graded cladding layer

To improve the output power and reduce electron leakage of a deep ultraviolet laser diode and optimize its performance,in this paper, the graded waveguide layer was first applied to a traditional AlGaN based deep ultraviolet laser diode, and four different combinations of the waveguide layer structure were simulated. Then a graded cladding layer structure with reduced thickness was added. Finally, the carrier concentration, energy band diagram, P-I curve, and optical confinement factor were numerically analysed and studied. The results demonstrate that, by using an Al-graded waveguide layer/p-cladding layer structure, the optical confinement factor of a laser diode with an emission wavelength of 267 nm, was 29.34%, and the maximum power was 89.81 mW at 100 mA current.

Efficient Composite Colorization of Copper by Spatially Controlled Oxidation with Deep‐UV Ultrafast Lasers

AbstractColorizing metals using micrometer and nanometer scale surface modifications has been vastly investigated and presents many advantages for applications across scientific and technological fields. By tuning the surface chemical composition or controlling its morphology, it is possible to produce a wide range of chromatic effects. Ultrafast laser processing presents here an interesting asset, as it allows to simultaneously provide chemical and morphological modifications at the micro‐scale in a single step. In this article, the composite colorization of copper surfaces with mW‐class average power deep ultraviolet (DUV) femtosecond laser pulses is demonstrated. The advantages of this setup are twofold: first, thanks to the increased absorption of copper in the DUV, the technique allows scaling down the requirement for laser power. Second, under ultrafast short‐wavelength illumination molecular oxygen bond‐breaks occur, enhancing the oxidation rate of the copper. The technique allows for highly controllable and efficient copper oxidation with the irradiation parameters. Taking these two effects into account, the generation of a wide spectrum of colors—from dark blue to shiny red—is demonstrated, and the role of the surface oxidation rate, the laser fluence, and laser scanning strategies in the colorization of copper surfaces employing DUV lasers is discussed.

Deep ultraviolet random laser disinfection

Recently, the ineffectiveness of conventional antibiotic treatments against multidrug-resistant bacteria stimulated the development of novel effective disinfection technologies. Ultraviolet lasers, with several features, including high coherence, high directionality, monochromatic, and high intensity, were the ideal candidate light source for disinfection; however, conventional lasers are restricted by their inherent detriments such as high directionality, meticulous manufacturing, and the laser speckles. Random lasers have been considered powerful candidates for illumination sources due to their angle-free emission in recent years. However, their practical application remains scarce, and the result of using a deep ultraviolet random laser (DUV-RL) for disinfection has not ever been reported. Herein, the DUV-RL is realized by applying AlGaN multiple quantum wells (MQWs) and aluminum nanoparticles as the gain medium and plasmonic scattering centers. The proof of concept for the first DUV-RL disinfection in our study is examined by implementing this unique light source on model gram-negative bacteria (Escherichia coli). Additionally, the inherent angle-free emission characteristic of random lasers was confirmed and applied in treatment to achieve angle-free disinfection, which enables random lasers to overcome the major drawback of the high directionality of conventional lasers. Above all, the success of applying random laser systems in the disinfection arena fulfills the empty piece of current laser treatment. This research is expected to promote the development of DUV-RLs and enable them to compete with other light sources, such as mercury lamps and Ultraviolet-C (UVC) LEDs, in the near future.