Search

High‐power blue‐emitting laser diodes have been used in projectors and lighting systems as excitation sources for yellow‐emitting phosphors. These phosphors must be robust and should not exhibit thermal quenching. In this work, we developed a durable eutectic phosphor consisting of single‐crystal Ce‐doped yttrium aluminum garnet (Ce:YAG) phosphor and Al2O3 (sapphire), with a thermal conductivity greater than 20 W/(m·K). This eutectic phosphor is named EPOCH‐Neo. EPOCH‐Neo specimens were cut from a large crystal substrate prepared by an edge‐defined film‐fed growth method. We evaluated the optical properties of EPOCH‐Neo specimens and the optical uniformity of an EPOCH‐Neo substrate. In addition, to control the chromaticity, the Y‐sites of Ce:YAG were doped with Gd at concentrations as high as 50% and the chromaticity and thermal characteristics of the resultant phosphors were evaluated. Moreover, the characteristics of a device composed of EPOCH‐Neo on a heatsink under blue laser excitation were examined. The results showed that EPOCH‐Neo is a durable phosphor suitable for use in high‐power‐excitation applications. [ABSTRACT FROM AUTHOR]

Background/Aim: Transgenic nude mice expressing green fluorescent protein (GFP), red fluorescent protein (RFP), or cyan fluorescent protein (CFP) were previously developed by our laboratory, AntiCancer Inc. In the present study, we demonstrate imaging of the GFP, RFP, or CFP nude mice with single-nanometer-tuning laser fluorescence excitation with a single instrument. Materials and Methods: Female transgenic C57/B6 nude GFP, RFP, and CFP mice aged six weeks were used. The images were obtained using the UVP Biospectrum Advanced system (Analytik Jena US LLC) with excitation at 480 nm and peak emission at 513 nm for GFP; 520 nm and 605 nm, respectively, for RFP; and 405 nm and 480 nm, respectively, for CFP. Results: For each color transgenic fluorescent mouse, images without background could be obtained individually with the UVP Biospectrum Advanced system. Conclusion: Using a single instrument, brilliant and well-defined images of GFP, RFP, and CFP mice were obtained with single-nanometer-tuning laser fluorescence excitation. This imaging system will be used in future studies to analyze cancer cells in the colored mice that are spectrally distinct in order to determine how stromal cells and cancer interact in the tumor microenvironment. [ABSTRACT FROM AUTHOR]

The thermoelastic wave propagation analysis is developed in a Love–Bishop nanorod resonator employing the strain gradient elasticity and Green–Naghdi theories with energy dissipation for the first time. The assumed nanorod resonator is subjected to thermal shock loading. The variational principle is applied to derive the coupled system of partial differential equations for temperature and displacement fields in a Love–Bishop nanorod. An analytical solution is proposed to solve the governing equations in Laplace domain. To obtain the temporal variation of fields' variables, a proper Laplace inversion technique is employed in the problem. The size effects in the nano-sized Love–Bishop rods are taken into account with five small-scale parameters including three higher-order materials length parameters, the micro-length inertia and thermal parameters. Two types of thermal shock loadings such as laser pulse-induced suddenly increasing temperature are utilized in this work, and the laser shock-induced thermoelastic wave propagations in both temperature and displacement fields are illustrated. The effects of the higher-order materials length parameters and the micro-length inertia and thermal parameters on the propagation of thermal and elastic waves are studied in detail. [ABSTRACT FROM AUTHOR]

Ultrafast electron dynamics have made rapid progress in the last few years. With Jellyfish, we now introduce a program suite that enables to perform the entire workflow of an electron‐dynamics simulation. The modular program architecture offers a flexible combination of different propagators, Hamiltonians, basis sets, and more. Jellyfish can be operated by a graphical user interface, which makes it easy to get started for nonspecialist users and gives experienced users a clear overview of the entire functionality. The temporal evolution of a wave function can currently be executed in the time‐dependent configuration interaction method (TDCI) formalism, however, a plugin system facilitates the expansion to other methods and tools without requiring in‐depth knowledge of the program. Currently developed plugins allow to include results from conventional electronic structure calculations as well as the usage and extension of quantum‐compute algorithms for electron dynamics. We present the capabilities of Jellyfish on three examples to showcase the simulation and analysis of light‐driven correlated electron dynamics. The implemented visualization of various densities enables an efficient and detailed analysis for the long‐standing quest of the electron–hole pair formation. This article is categorized under:Theoretical and Physical Chemistry > SpectroscopySoftware > Simulation Methods [ABSTRACT FROM AUTHOR]

We introduce a new non-symmetric-in-time version of the second Demkov–Kunike model. This is a constant-amplitude level-crossing field configuration, where the detuning varies in a restricted frequency interval and crosses the resonance in a non-symmetric way with respect to the crossing time point. We provide the solution of the two-state problem for this field configuration using irreducible linear combinations of hypergeometric functions and calculate the transition probability at time going to infinity for the scenario where the system begins in the first quasi-energy state. [ABSTRACT FROM AUTHOR]

This study focuses on source term inversion in fractional partial differential equations, specifically applied to photoacoustic imaging. This work contributes to advancing imaging techniques and provides practical insights for medical diagnostics and materials characterization. Our aim in this paper is to develop an accurate method for recovering the location and the shape of a laser excitation source from partial boundary data. To achieve this, we reformulate our inverse problem as an optimization challenge. We utilize topological sensitivity analysis to establish an asymptotic expansion of a relevant shape function. These theoretical findings form the basis for a rapid and precise detection algorithm. Additionally, we present several numerical experiments that demonstrate the effectiveness and accuracy of our proposed approach. [ABSTRACT FROM AUTHOR]

A high-resolution frontside fault isolation methodology for the analysis of wafer-to-wafer (W2W) hybrid bonding interconnects in three-dimensional integration is reported. The approach utilizes the visible light optical beam induced resistance change (VL-OBIRCH) method and incorporates a localized substrate removal technique, eliminating the need for a costly backside approach that requires a solid immersion lens. The top silicon substrate is removed using laser lithography and selective etching techniques, enabling the utilization of 405 nm excitation light for the VL-OBIRCH analysis. The validity of the methodology is demonstrated on W2W interconnect test structures with varying interconnect pitch and pad dimensions. The effectiveness of the proposed approach is confirmed through cross-sectional analysis. [ABSTRACT FROM AUTHOR]

Enabling simultaneous and high-resolution quantification of the total concentration of hemoglobin ($\text{C}_{{\text {Hb}}}$), oxygen saturation of hemoglobin (sO2), and cerebral blood flow (CBF), multi-parametric photoacoustic microscopy (PAM) has emerged as a promising tool for functional and metabolic imaging of the live mouse brain. However, due to the limited depth of focus imposed by the Gaussian-beam excitation, the quantitative measurements become inaccurate when the imaging object is out of focus. To address this problem, we have developed a hardware-software combined approach by integrating Bessel-beam excitation and conditional generative adversarial network (cGAN)-based deep learning. Side-by-side comparison of the new cGAN-powered Bessel-beam multi-parametric PAM against the conventional Gaussian-beam multi-parametric PAM shows that the new system enables high-resolution, quantitative imaging of $\text{C}_{{\text {Hb}}}$ , sO2, and CBF over a depth range of $\sim 600~\mu \text{m}$ in the live mouse brain, with errors 13–58 times lower than those of the conventional system. Better fulfilling the rigid requirement of light focusing for accurate hemodynamic measurements, the deep learning-powered Bessel-beam multi-parametric PAM may find applications in large-field functional recording across the uneven brain surface and beyond (e.g., tumor imaging). [ABSTRACT FROM AUTHOR]

YAG: Ce3+ phosphor/silicone composites are widely used in solid-state lighting as a light converter to achieve white lighting. However, because of high thermal resistance and low thermal stability, the luminous performance of YAG: Ce3+ phosphor/silicone composite deteriorates rapidly when excited by high-power-density blue-laser. To explore the potential of blue laser-excited YAG: Ce3+ phosphor/silicone composites, the luminous performances under different blue laser power conditions were characterized by both the reflective and transmissive excitations using a self-built three-integrating-sphere system. Furthermore, the Monte-Carlo Ray-tracing simulation was used to illustrate the light-transmission and energy conversion mechanism in the phosphor/silicone composites. The results showed that: (1) The YAG: Ce3+ phosphor/silicone composite could be excited by the 0.292W laser light with the peak wavelength of 445nm, excessive laser power will cause phosphor thermal quenching and silicone carbonization. (2) The luminous flux of the composite under both the reflective and transmissive excitations gradually increased with the increase of phosphor concentration; correspondingly, the color coordinate moved to the yellow region, and the Correlated Color Temperature (CCT) gradually decreased. (3) The simulation results indicated that under the same phosphor concentration, the luminous flux obtained by reflection excitation was largely higher than that by the transmission excitation, as the light re-conversion and strong back-scattering were occurred in the reflective and transmissive laser excitation respectively.

The demands for integrated communication and positioning (ICP) have been put forward in Internet of Things. However, the existing ICP systems either face challenges in trade-off between data rates and positioning accuracy or have difficulties in guaranteeing human safety while maintaining excellent performance. In this paper, we propose a monocular resonant beam-based ICP (RB-ICP) design for simultaneously realizing high-rate data transfer and high-accuracy localization while keeping the features as intrinsic safety. Utilizing the high-efficiency transmission channel of resonant beam system and the frequency-doubled beam design, we introduce the communication model without the echo interference issue. Then, we propose a distance estimation model using the phase-shift method with frequency-quadrupled beam design. Next, the angle of arrival estimation can be conducted relying on the energy-concentrated and self-alignment features of resonant beam. The simulation methods including centroid algorithm and signal conversion simulation in a photosensor along with the noise analysis are presented. In numerical analysis, we demonstrate that the positioning error can be less than 1cm and the achievable spectral efficiency can reach 16bit/s/Hz over 2m distance in 15° field of view (FoV). This proposed system enables simultaneous high-rate data transfer and high-accuracy receiver positioning for the applications such as augmented reality/virtual reality (AR/VR). [ABSTRACT FROM AUTHOR]

High-power mid-infrared 2.8- $\mu \text{m}$ ultrafast laser has potential applications in the fields of laser surgery due to its wavelength overlap with the absorption peak of water. In this work, we demonstrate a 2.8- $\mu \text{m}$ picosecond Raman laser in a methane-filled hollow-core anti-resonant fiber (HC-ARF) with average power of 4 W, pulse energy of 40 $\mu \text{J}$ , and beam quality of 1.47. The laser beam quality improvement at mid-infrared Raman conversion in methane-filled HC-ARF is firstly observed. This work heralds a promising approach to generate mid-infrared ultrafast Raman laser with multi-Watt level average power and high beam quality. [ABSTRACT FROM AUTHOR]

We report a compact ultrafast solid-state laser source with a pulse repetition rate continuously tunable in the range of 0.56–1.23 GHz. The optical cavity design allows a user to vary the repetition rate only by moving positions of two optical components inside the resonator, without a need to exchange components or realignment. The Yb:KYW crystal based cavity emits 250 femtosecond pulses at a central wavelength around 1040 nm, with a self-starting SESAM modelocking. In a robust modelocked operation mode, an average power up to 130 mW is achieved using a stabilized single mode pump diode at a wavelength of 981 nm, while the laser in continuous wave (CW) mode delivers up to 270 mW. Atmospheric air cooling was sufficient for both CW and modelocked laser operation. Quite low noise performance was observed, with carrier frequency SNR higher than 80 dB, although the measurements were taken with the open breadboard setup. [ABSTRACT FROM AUTHOR]

We report an in-well and barrier coupling pump scheme of semiconductor disk laser (SDL). An in-well-absorbed (940 nm) and a barrier-absorbed (808 nm) pump source were used to measure laser output characteristics. The output power of the coupling pump can be significantly improved compared to the in-well pump only scheme under similar thermal load conditions. The power scaling of the coupling pump SDL is caused by the interaction dynamics of the photoexcited carrier between quantum-well and barrier. The results are discussed with a rate equation model that considers the injected into the quantum-well carrier and the barrier carrier in the active region. [ABSTRACT FROM AUTHOR]

Q-switching in a mode-locked laser not only makes the amplitude of every single output pulse unequal, but also limits the time width and peak power of output pulses. This paper investigates the Q-switching in a self-mode-locked semiconductor disk laser numerically and experimentally. By using the delay differential equations for passively mode-locking, conditions of Q-switching in a self-mode-locked semiconductor disk laser are numerically analyzed for the first time. Meanwhile, based on the experimental results, the causes of Q-switching tendency including the change of nonlinear refractive index and the change of soft aperture, are also discussed. Some possible measures to suppress Q-switching instability, i.e., to obtain stable continuous-wave mode-locking in a self-mode-locked semiconductor disk laser are proposed. [ABSTRACT FROM AUTHOR]

An optical resonator with a spiral-phase defect is proposed for vortex laser generation. Theoretical models and calculations were conducted to predict the topological charge distribution of the emitted vortex laser. Utilizing a reflective spatial light modulator that creates a spiral-phase defect of variable radius and azimuthal phase modulation, vortex beams with controllable topological charges and intensity distributions were demonstrated experimentally. [ABSTRACT FROM AUTHOR]

Phosphor-converted white laser diode (WLD) is considered as a promising light source in next-generation high-brightness lighting. However, the WLD suffers from low optical quality in luminous efficacy and color rendering. In this work, we fabricated a high-quality WLD by a blue laser-driven a tricolor phosphor-in-glass (PiG) film-on-sapphire (PIGS). The tricolor PiGS was prepared by sintering a green/yellow/red phosphor glass film on a sapphire substrate. The optical quality of tricolor PiGS-WLDs were optimized by adjusting the phosphor ratio. At the phosphor ratio of 9:6:1, the PiGS-WLD achieves high optical quality with a luminous flux of 362.1 lm, a color rendering index (CRI) of 80.3, and a correlated color temperature (CCT) of 4590 K at a laser power of 2.4 W. The PiGS-WLD has the highest luminous efficacy of 154.5 lm/W at 3.15 W. Furthermore, the PiGS-WLD displays excellent color stability with small CCT and CRI deviation under various laser powers and continuous excitation. The surface temperature of PiGS-WLD is stable at 104 °C due to the high thermal conductivity of sapphire substrate. Therefore, this study provides a stable and high-quality laser-driven white light source for high-brightness lighting and display. [ABSTRACT FROM AUTHOR]

Purpose: This work aims at investigating the zinc atoms in the triplet preionization – Rydberg states. The energy levels of atoms having two electrons outside the closed shell were studied mainly by the optical spectroscopy methods. However, just using the microwave spectroscopy to measure the frequency of transitions between the two Rydberg states allows to increase the accuracy of measurements in two or more orders of magnitude. Disign/methodology/approach:A line of three dye lasers is used to excite the zinc atoms into the triplet Rydberg states with a predetermined set of quantum numbers. The radiation of the first two of them is transformed into the second harmonic in nonlinear crystals. Dye lasers are excited by the radiation of the second harmonic of one YAG: ND3+ laser. All three radiations are reduced to the zone of interaction with the laser and the microwave radiation, which is located between the plates of the ionization cell, where the pulsed electric field is created. The excited Rydberg atoms are recorded with the field ionization procedure. The beam of neutral atoms is created by an effusion cell under the vacuum conditions, the residual pressure does not exceed 10-5 mm Hg. A pulsed electric field of some certain intensity results inionization of atoms excited by microwave radiation and in acceleration of electrons, which have appeared in the direction of the secondary electron multiplier, though being insufficient for ionization of atoms excited only by the laser radiation and which are initial for interaction with microwaves. By scanning the microwave radiation frequency with the given step and measuring the signal intensity of the secondary electron multiplier, the excitation spectrum of the atoms under study can be obtained. Findings: Using the created laser-microwave spectrometer, the frequencies of the F→D, F→F and F→G transitions between the triplet Rydberg states of zinc atoms were measured. From the analysis made of the transition frequencies, the quantum defect decomposition constants were obtained by the Ritz formula for the D, F, and G states of zinc atoms. Conclusions: The frequencies of the F→D, F→F and F→G transitions between the triplet Rydberg states of zinc atoms were measured that allowed obtaining the quantum defect decomposition constants according to the Ritz formula for the D, F and G states of zinc atoms, that in turn had allowed to calculate the energy of these terms and the transition frequencies at least in two orders of magnitude more accurately as against the similar measurements made by the optical spectroscopy.

In this paper, we demonstrated a high-brightness bidirectional tandem-pumped confined-doped fiber amplifier with nearly 8 kW output power. The technical difficulties for realizing the bidirectional tandem-pumping scheme are comprehensively analyzed, according to which, the homemade high signal-isolation side-coupled pump and signal combiner as well as stable 1018 nm pump sources were developed and applied in the experimental study, successfully enabling the first demonstration of the bidirectional tandem pumping scheme. Moreover, benefiting from the confined-doped fiber design and the bidirectional tandem pumping technique, the transverse mode instability was successfully mitigated and the beam quality was well preserved during the power scaling process. Eventually, an output power of 7.88 kW was obtained with the beam quality factor of ∼1.97 and the optical-to-optical efficiency of ∼84.76%. This work provides a good reference for realizing large-mode-area fiber lasers with high output power and good beam quality by utilizing the confined-doped fiber design and bidirectional tandem-pumping technique. [ABSTRACT FROM AUTHOR]

SO2F2 and SOF2 are important characteristic decomposition components of SF6. Accurate detection of these two gases is helpful for fault diagnosis of gas-insulated switchgear (GIS). In this article, the infrared characteristic peaks of SO2F2 and SOF2 were obtained by comparing the simulation and experimental infrared spectrum. Then, cross interference analysis was performed with SF6 characteristic components such as H2S, SO2, CO, and SF6 background gas to determine the appropriate detection bands for SO2F2 and SOF2. Tunable diode laser absorption spectroscopy (TDLAS) experiment platform was built based on quantum cascade laser with center wavelength at 1506.4 and 1340.2 cm−1. The concentration of SO2F2 and SOF2 is detected through this platform. And the concentration information of gas is deduced by detecting the voltage value of second harmonic signal. The experimental results show that, for SO2F2 gas between 1.01 and 19.88 ppm, the $R^{2}$ is 0.989 and the maximum relative error is 2.044%. For SOF2 gas between 1.03 and 9.00 ppm, the ${R}^{{2}}$ is 0.992 and the maximum relative error is 0.728%. SO2 gas may cause weak interference to SOF2 detection, which has some regularities, and the interference can be eliminated by selecting the appropriate SOF2 fitting linear equation. The research results provide a feasible scheme for the quantitative detection of SO2F2 and SOF2 gases. [ABSTRACT FROM AUTHOR]

Whispering gallery mode (WGM) microcavities can efficiently store and manipulate light with strong light confinement and long photon lifetime, while coupling light into and from WGMs is intrinsically hindered by their unique feature of rotational symmetry. Here, a scattering-assisted liquid crystal (LC) micropillar WGM laser is proposed. WGM lasing at the surface of the micropillar is obviously enhanced by fluorescence scattering in the core of the micropillar. Besides, weak scattering of LC molecules also builds efficient coupling channels between the laser modes and the axial transmission modes of the micropillar-based waveguide, providing an all-in-one liquid WGM laser with functions of self-seeding and self-guiding. Furthermore, based on the hysteresis characteristics of the electrically anchored LC molecules under the interaction of thermal force, an erasable read-write liquid memory device is proposed, paving the way for the application of logic-controllable WGM lasers in optical storage and optical control. [ABSTRACT FROM AUTHOR]

Results of calculation of the absorption spectrum of phosphorus oxide (PO) corresponding to the A2Σ+ (v′ = 0) − X 2Π (v′′ = 0) transition are presented. The calculation is performed taking into account the perturbation of the v′ = 0 level of the A2Σ+ state by the v′ = 4 level of the b4Σ− state. The efficiency of laser excitation of PO molecules is estimated as a function of the spectral parameters of the radiation. The time dependence of the efficiency of the excitation of PO fragments is calculated for a real atmosphere under two-pulse laser fragmentation of organophosphates for specified spectral linewidths Δλ and center positions λ0. [ABSTRACT FROM AUTHOR]

We demonstrate the versatility of our recently demonstrated technique of Stimulated Raman Scattering induced simultaneous wavelength conversion and power combining of multiple Ytterbium (Yb) doped fiber lasers in terms of number of input pump sources and the wavelength spacing between them. We experimentally show that this technique works when the Raman gain coefficient between the input chosen pump sources is 1) negligible, i.e., when pump sources are separated in wavelength by as small as 5nm, 2) approximately half of the peak value, and 3) more than half of the peak value. Our experiments also show that the technique works for more than two Ytterbium-doped fiber lasers. Experimental results were shown for power combining of 1074nm and 1079nm lasers, 1088nm and 1117nm lasers, and 1074nm, 1088nm and 1117nm lasers with >80% of the power in the $1.5~\mu \text{m}$ band in each case. Also, through simulations, we elucidate the reasons for asymmetric Raman gain that is responsible for power combing and show power combining of 6 pump sources, with arbitrary wavelength spacing showing the versatility of this technique. [ABSTRACT FROM AUTHOR]

Compared with Yb, Nd has potential in 1120 nm fiber lasers, with the characteristics of larger emission cross section and four-level structure. In this work, Nd-doped fiber (NDF) oscillator and Nd-Raman fiber (NRF) oscillator were built using single-mode 5/125 NDF to study the lasing characteristics at 1120 nm, especially the suppression of amplified spontaneous emission at 1060 nm. Limited by the parasitic oscillation at 1060 nm, the NDF oscillator achieved 5 W output at 1120 nm. The NRF oscillator removed the limitation due to the Raman shift from 1064 nm to 1120 nm and obtained an output of 7.7 W at 1120 nm with a spectral peak-to-peak contrast of 36 dB. This work provides experimental basis for the application of NDF in 1.1 μm. [ABSTRACT FROM AUTHOR]

It is generally impossible to maintain tight focusing over a long distance because of diffraction; this so-called Rayleigh's curse may be broken for a femtosecond laser if the wavefront curvature varies with laser wavelength. This paper reports on a nonlinear technique to produce a wavelength-dependent wavefront. We reveal a wavelength-dependent wavefront mechanism that is induced in optical parametric chirped-pulse amplification (OPCPA) where the crystal effect of group-velocity mismatch (GVM) dominates. Both analytical and numerical investigations show that the sign of the produced wavefront can be changed by GVM, and the magnitude can be enhanced by multistage OPCPA. The results suggest that the Rayleigh range at a fixed beam waist size can be significantly increased by the OPCPA-induced wavelength-dependent wavefront. [ABSTRACT FROM AUTHOR]

We report a widely tunable pulsed dysprosium (Dy) -doped fluoride fiber laser within a 545 nm continuous wavelength range around 3 μm, where a home-made random Raman fiber laser (RRFL) at 1.690 μm acts as the pump, and a commercial InAs saturable absorber (SA) is adopted as the Q-switcher. The designed RRFL, excited by a 1.055 μm ytterbium-doped fiber oscillator, can provide the 8th order Stokes emission at 1.690 μm with a high spectral purity of 98.6% and a maximum output power of 14.4 W. Feeding it to a Dy cavity involving an InAs SA and a ruled diffraction grating in a Littrow configuration, stable Q-switching can be initiated and tuned within the continuous/total range of 2.775∼3.320 μm (545 nm)/2.765∼3.338 μm (573 nm), an extension of 50% over the prior 370 nm record [Opt. Lett., vol. 44, no. 9, pp. 2322-2325, 2019], representing the widest level to date from a pulsed rare-earth-doped laser at any wavelengths, to the best of our knowledge. When the wavelength is tuned to 2.992 μm, a maximum average power of 106 mW with 460 ns pulse width, 125 kHz repetition rate, and 0.85 μJ pulse energy is achieved. This work marks the first pulsed Dy-doped fluoride fiber laser pumped at ∼1.7 μm while exhibiting the utility of InAs in pulse generation at the wavelengths of 3∼3.4 μm for the first time, to the best of our knowledge. The demonstration highlights the great potential of ∼1.7 μm pumped Dy-doped fluoride fiber laser as a platform for developing widely tunable pulsed sources in the 3 μm region of the mid-infrared. [ABSTRACT FROM AUTHOR]

A 10 kW fiber amplifier seeded by the random fiber laser (RFL) with 1018 nm tandem-pumping scheme is reported in this letter. The amplified RFL centered at 1085 nm is seeded by the RFL with a full-open cavity. An array of chirped and tilted fiber Bragg gratings placed before the main amplifier prevent the stimulated Raman scattering with a suppression ratio of 55.8 dB. Control experiments prove that the fiber amplifier seeded by the RFL can suppress the spectral broadening during the amplification process effectively. We demonstrate experimentally that this phenomenon is due to the better temporal stability of the RFL compared with that of the fixed-cavity fiber laser. This fiber amplifier seeded by the RFL is the highest output power record for the amplified RFL to the best of our knowledge, and the spectral evolution suggests the potential for further power scaling-up. [ABSTRACT FROM AUTHOR]

A passively Q-switched Nd:YAG/Cr:YAG microchip laser with the pulse duration of < 200 ps has been developed. To obtain such short pulses from Nd:YAG/Cr:YAG microchip lasers, a numerical model based on rate equations was introduced and a design strategy of microchips was discussed. Since the pump bleaching effect in Cr:YAG leads to an increase of output pulse duration, a method of small-spot pumping was employed to reduce the effect and shorten the pulse duration. In the experiments, 1064-nm laser pulses with the duration of 153 ps and the energy of 18 $\mu \text{J}$ at 4.5 kHz was achieved. A good beam quality of $M^{2} =1.15$ was also measured. [ABSTRACT FROM AUTHOR]

In this Letter, we used a home-made high-power and -brightness random Raman fiber laser (RRFL) at $1.69~\mu \text{m}$ as the pump to demonstrate free-running and widely tunable operations of dysprosium (Dy)-doped ZrF4 fiber laser in the 3 $\mu \text{m}$ mid-infrared (MIR) region. In an optimal F-P cavity arrangement, the maximum output power of 1.92 W with a slope efficiency of 18.3% was achieved at 2.992 $\mu \text{m}$ , indicating the highest power level of Dy fiber lasers under near-infrared (NIR) pumping. Using a modified scheme, in which a ruled diffraction grating (RDG) in a Littrow configuration was adopted as the wavelength selector and output coupler, the laser wavelength could be continuously tuned in the >700 nm range of $2.710\sim 3.415~\mu \text{m}$ , almost entirely covering the emission bands accessed by erbium (Er) and holmium (Ho) ions in this region. To our knowledge, this is the widest level (in terms of wavelength domain), to date, from not only a Dy laser, but a rare-earth-doped laser at any wavelengths. Additionally, the possibility of further extending the tuning range has been also predicted by preliminary modeling, validated by the experimental data. These results highlight the great potential of this NIR pumped Dy fiber laser for developing high-performance coherent source at $\sim 3~\mu \text{m}$. [ABSTRACT FROM AUTHOR]

A detailed analysis of theexcited state absorption (ESA) transition 4I13/2→4I9/2 which occurs in erbium (Er) doped ZBLAN fiber lasers is performed through numerical modeling. It is found that the ESA plays a significant role in enhancing the 2.8 μm lasing of Er3+ ions. The ESA promotes the ions residing in 4I13/2 (the lower state of the 2.8 μm laser) to 4I9/2, where the ions subsequently decay to 4I11/2 (the upper state of the 2.8 μm laser) rapidly. An energy recycling is consequently realized via the ESA. The ESA can be activated in cascaded 2.8 μm/1.6 μm Er-doped ZBLAN fiber lasers by absorbing the 1.6 μm signal. Through numerical simulation it is found that in cascaded lasers the slope efficiency of the 2.8 μm laser can be elevated to ∼48% with the assistance of the ESA, a value that surpasses the Stokes limit (∼35%) substantially and agrees well with the experimental results previously reported. It is also found that the ESA-induced energy recycling is exothermic, an effect that is non-ignorable in the high-power circumstance. Moreover, the injection of an additional 1.6 μm pump for directly exploiting the 4I13/2→4I9/2 ESA is simulated using the model. It is found that as the second pump is introduced, the 2.8 μm lasing almost entirely relies on the ESA-induced energy recycling, and hence, the laser is capable of operating under very low 976 nm pump power. The simulation results indicate that the 2.8 μm lasing in Er-doped ZBLAN fiber lasers can even be realized using a single 1.6 μm pump, via a combination of the 4I15/2→4I13/2 and 4I13/2→4I9/2 transition. The outcomes of this work can inspire the development of novel, high-performance 2.8 μm Er-doped ZBLAN fiber lasers. [ABSTRACT FROM AUTHOR]

In this work, a novel configuration of a photothermal gas sensor is demonstrated. The measured gas sample is delivered to a gas cell placed inside the linear cavity of a 1.55 μm mode-locked fiber laser. The gas refractive index modulation resulting from the excitation by an auxiliary continuous wave laser is efficiently probed by analyzing the phase shift of the self-heterodyne beatnote signal of the mode-locked laser. IQ demodulation combined with Wavelength Modulation Spectroscopy-based signal analysis was employed to optimize and simplify the spectroscopic data acquisition and analysis. A proof-of-concept experiment with detection of carbon dioxide at 2 μm wavelength yielded a noise equivalent absorption of 2.25·10−7 for 1000 s integration time. The proposed sensor configuration is versatile and can be used to probe any gas molecule, provided an appropriate excitation source is used to induce the photothermal effect. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a novel method to achieve pulsed operation of thulium-doped fiber lasers at 1.7 μm. In our design, the thulium-doped fiber laser cavity was embedded within the cavity of an erbium/ytterbium-codoped fiber laser operating at 1.5 μm. The thulium-doped fiber in the erbium/ytterbium-codoped fiber laser cavity served as a saturable absorber, forcing the 1.5 μm laser to operate in a passively Q-switched scheme. The 1.7 μm thulium-doped fiber laser was in-turn pumped by the Q-switched 1.5 μm laser and was gain-switched. This made the pulse duration of 1.7 μm emission much shorter than that of 1.5 μm emission. 1.02 W average output power at 1720 nm was obtained for 10 W of pump power at 976 nm. The pulse repetition frequency, pulse energy and pulse duration were 134 kHz, 7.6 μJ and 102 ns, respectively. A rate equation model was developed to examine the power- and temporal-behavior of the laser system. The calculated pulse duration and pulse repetition frequency matched well with the experimental results. Methods of further improving the laser performance are discussed based on insights gleaned from our modeling. [ABSTRACT FROM AUTHOR]

Deep ultraviolet (DUV) lasers are essential elements to versatile applications such as spectroscopy and lithography, and several techniques including free-electron lasers, excimer lasers and high-order harmonic conversion have been developed for DUV laser generation, yet the wavelength tunability and compactness are still challenging. Here, for the first time, we experimentally demonstrate a compact tunable continuous-wave (CW) DUV laser source by direct intracavity frequency doubling of visible fiber lasers. Efficient green/yellow laser emission is enabled by the down-conversion in the Ho $^{3+}$ - or Dy $^{3+}$ -doped ZBLAN fibers while the miniaturized cavity consists of a home-made fiber pigtail mirror and diffraction grating. The second harmonic generation from visible to ultraviolet is subsequently implemented by utilizing a BBO module intracavity. The achieved CW DUV lasers yield wavelength tuning range of 269.5-275.4 nm and 283.6-289.9 nm in the presence of an ultra-narrow linewidth of $< $ 0.025 nm. The produced power at 272.6 nm reaches 1.36 mW and a maximum visible-to-DUV efficiency of 5.3‰ is estimated with the green laser excitation. Our work therefore provides new possibilities for the realization of a new class of compact, wavelength tunable, and cost-effective CW DUV laser sources. [ABSTRACT FROM AUTHOR]

To achieve a high spectral purity Raman laser in a wide range of pump power, we propose the adjustable Raman threshold method and experimentally demonstrate a 6.85 kW ytterbium-Raman (Yb-Raman) fiber amplifier in this paper. The Raman threshold is adjusted to coordinate with pump power level via manipulating the Raman proportion from the master oscillator. The spectral purity of Raman laser at 1120 nm reaches 86.0 $\%$ at the highest output power and keeps over 65 $\%$ throughout. And the 3 dB bandwidth is maintained within 2.5 nm. The system shows potential in further power scaling-up because the four-wave-mixing-induced high-order Raman noise is circumvented by designing wavelengths of the seeders. This work not only reports the highest output power of the Yb-Raman fiber lasers (to the best of our knowledge), but also provides an approach to achieve an agile lasing threshold in the Yb-Raman fiber amplifiers without any structural adjustments. The Yb-Raman fiber amplifiers with high spectral purity over a broad range of power will have promising applications in communications, industry and scientific researches. [ABSTRACT FROM AUTHOR]

This article presents the spatial and temporal dynamics of high-power Gaussian laser pulse in relativistic plasma. At higher intensities, the self-focusing and self-compression of laser pulse take place due to the variation in the mass of plasma electrons moving with speed comparable to the speed of light. The two non-linear coupled differential equations for spatial and temporal pulsewidth parameters have been obtained using the moment theory approach. These equations have been solved numerically using the Runga–Kutta method. The variation in the spatial and temporal pulsewidth parameters with the distance of propagation is then used to calculate the energy gained by the electrons, which are trapped by the excited electron plasma wave during laser–plasma interaction. It is observed that spatio-temporal dynamics play an important role in electron acceleration in relativistic plasma. [ABSTRACT FROM AUTHOR]

A pump–probe system with a subnanosecond pulsed laser is expected to be a compact and inexpensive transient spectroscopic system that enables nondestructive and noncontact evaluations of the physical properties. However, an improvement in the sensitivity and a theoretical model to complement the measurement signal are necessary to obtain the transient signal precisely because of the low sensitivity and large time resolution. We have developed a highly sensitive pump–probe system with a subnanosecond pulsed laser that combines signal amplification based on surface plasmon resonance (SPR) in this study. An integrated theoretical model of the transient response obtained by a subnanosecond pump–probe under the SPR condition was proposed. Our model consisted of the profile descriptions of the used pulse source, temperature change, generated thermoelastic stress, estimated permittivity change in the metal film, and estimated reflectivity change. The theoretical estimations in the time domain and the incident angle dependence were compared with those of the experimental results to verify our theory. As a result, the estimations were well in agreement with the experimental results. Moreover, the signal-amplification mechanism based on SPR was discussed using our theory. The amplification was caused by the broadening of the resonant curve of SPR and the shift of the resonant angle, which seemed to come from the increase in the electron–phonon scattering rate and the thermal expansion of the metal film, respectively. A clear mechanism of SPR-based signal amplification of the subnanosecond pump–probe was identified through experimental and theoretical approaches. [ABSTRACT FROM AUTHOR]

Combining the benefits of photothermal conversion in a doped optical fiber with the principle of Fiber Bragg Grating (FBG)-based temperature measurement, a new optical fiber method for the measurement of moisture content has been developed and its performance is reported. This novel all-fiber approach shows the important characteristics of fast response, miniaturization in the design and low power consumption. In this work, a 1480nm pump laser has been used to heat the cobalt-doped fiber used, which has been embedded in the sample under investigation, where the sensor temperature change was obtained by using a FBG written into the cobalt-doped fiber. The fast, in-situ measurement of moisture content developed takes advantage of the linear relationship between the temperature change characteristics experienced during the heating process and the moisture content. To calibrate and characterize the sensor developed, a variable moisture-content test platform was established, and experiments were conducted to investigate the performance of this optical fiber approach. The all-fiber moisture sensor developed in this way has been evaluated by measuring the moisture content of samples of soil and pulverized coal and the data obtained were in good agreement with the results obtained from using the more conventional (and slow) drying method, with a maximum error of just over 1% and a rapid, 2s, optimum measurement time achieved. [ABSTRACT FROM AUTHOR]

The effect of seed power on the inter-modal four-wave mixing (IM-FWM) effect in a distributed side-pumped fiber amplifier is investigated for the first time, to the best of our knowledge. By using a seed source smaller than 70 W, the effect of seed power on the IM-FWM is studied experimentally. Surprisingly, it is found that the IM-FWM effect becomes stronger with the weaker seed. To analyze the physics behind this result, a numerical model is introduced, and the numerical results are in good agreement with the experimental observations. It is revealed that the IM-FWM enhancement is induced by the gain competition between the signal light and the anti-Stokes light of the IM-FWM. It is also found that there is an optimized seed power for suppressing the IM-FWM effect. The experimental and numerical results which are presented in this work can provide significant guidance for understanding the IM-FWM in fiber lasers and amplifiers. [ABSTRACT FROM AUTHOR]

Terahertz band in electromagnetic spectrum has many properties than traditional light source, which has very important research value in biology, material, security, communication and other fields. The high power and high efficiency terahertz radiation source is an important factor and prerequisite for the transformation of terahertz technology into actual productivity. In this paper, the research progress of terahertz wave generated by laser interacting with different excitation media is summarized from the perspective of gas, solid and liquid as excitation media. The physical mechanism of four-wave mixing, mass-dynamic, cherenkov and photocurrent models commonly used in gas media, as well as the physical mechanism of photo-conductance and photorectification models in solid media are described in detail, and the factors affecting the generation of terahertz waves by these excitation media are analyzed and summarized. Finally, the methods of producing terahertz radiation source by liquid excited medium are prospected.

The Quantum Scientific Computing Open User Testbed (QSCOUT) at Sandia National Laboratories is a trapped-ion qubit system designed to evaluate the potential of near-term quantum hardware in scientific computing applications for the U.S. Department of Energy and its Advanced Scientific Computing Research program. Similar to commercially available platforms, it offers quantum hardware that researchers can use to perform quantum algorithms, investigate noise properties unique to quantum systems, and test novel ideas that will be useful for larger and more powerful systems in the future. However, unlike most other quantum computing testbeds, the QSCOUT allows both quantum circuit and low-level pulse control access to study new modes of programming and optimization. The purpose of this article is to provide users and the general community with details of the QSCOUT hardware and its interface, enabling them to take maximum advantage of its capabilities.

As COVID-19 has increased the need for connectivity around the world, researchers are targeting new technologies that could improve coverage and connect the unconnected in order to make progress toward the United Nations Sustainable Development Goals. In this context, drones are seen as one of the key features of 6G wireless networks that could extend the coverage of previous wireless network generations. That said, limited onboard energy seems to be the main drawback that hinders the use of drones for wireless coverage. Therefore, different wireless and wired charging techniques, such as laser beaming, charging stations, and tether stations, are proposed. In this article, we analyze and compare these different charging techniques by performing extensive simulations for the scenario of drone-assisted data collection from ground-based Internet of Things devices. We analyze the strengths and weaknesses of each charging technique, and finally show that laser-powered drones strongly compete with, and outperform in some scenarios, other charging techniques. [ABSTRACT FROM AUTHOR]

Objective: Currently available ventricular assist devices provide continuous flow and do not adapt to the changing needs of patients. Physiological control algorithms have been proposed that adapt the pump speed based on the left ventricular pressure. However, so far, no clinically used pump can acquire this pressure. Therefore, for the validation of physiological control concepts in vivo, a system that can continuously and accurately provide the left ventricular pressure signal is needed. Methods: We demonstrate the integration of two pressure sensors into a tapered inflow cannula compatible with the HeartMate 3 (HM3) ventricular assist device. Selective laser melting was used to incorporate functional elements with a small footprint and therefore retain the geometry, function and implantability of the original cannula. The system was tested on a hybrid mock circulation system. Static and simulated physiological flow and pressure profiles were used to evaluate the combined pressure and flow sensing capabilities of the modified cannula. Results: The cannula prototypes enabled continuous pressure measurements at two points of their inner wall in the range of −100 and 200 mmHg. The developed, Bernoulli-based, two sensor model improved the accuracy of the measured simulated left ventricular pressure by eliminating the influence of flow inside the cannula. This method reduced the flow induced pressure uncertainty from up to 7.6 mmHg in single sensor measurements to 0.3 mmHg. Additionally, the two-sensor system and model enable the measurement of the blood flow through the pump with an accuracy of −0.14 ± 0.04 L/min, without dedicated flow sensors. [ABSTRACT FROM AUTHOR]

Acoustic wave coupling in dual-wavelength orthogonal polarized Brillouin random fiber laser (BRFL) based on polarization-maintaining (PM) fiber is characterized experimentally for the first time. Dual-wavelength BRFL is generated when the pump light is injected to the Brillouin gain PM fiber at 45 degrees from the slow axis. The dynamics of intensity and frequency of dual-wavelength and single-wavelength BRFLs are investigated. The spectrum of Pearson’s correlation coefficient between different frequencies of the dual-wavelength BRFL shows several correlation peaks due to gain competition of two spatially overlapped coupled modes induced by acoustic wave coupling. The dual-wavelength BRFL presents a lower laser frequency drift with a standard deviation of 2.55 MHz and a larger relative intensity fluctuation with a standard deviation of 0.54 compared with that of single-wavelength BRFL (3.68 MHz and 0.32), which is attributed by increased photon-phonon coupling over the Brillouin gain fiber resulting from the coupling of acoustic waves in fast and slow axis due to 45 degrees pumping. In addition, replica symmetry breaking (RSB) is observed in dual-wavelength BRFL due to the increased gain competition of more random modes from acoustic wave coupling, which leads to correlated intensity fluctuations from trace to trace. The exploration of the internal spectral correlation, intensity fluctuation, RSB and frequency drift exposes the acoustic wave coupling in the dual-wavelength Brillouin random lasing process. [ABSTRACT FROM AUTHOR]

We report on an in-band-pumped Dy-doped ZBLAN fiber laser with tunable emission wavelength in the mid-IR range from 2.925 to 3.250 $\mu$ m and single-frequency operation. Using the combination of an intracavity germanium etalon and a reflective diffraction grating, we demonstrate the selection of single-frequency operation with emission linewidth narrower than 110 kHz, maximum output power of $\sim 40$ mW, and relative intensity fluctuations at a level of 0.9% over an integration bandwidth from 1 Hz to 10 MHz. [ABSTRACT FROM AUTHOR]

Soft-glass fiber lasers have attracted lots of attentions as they are most likely to achieve compact, stable, and highly efficient mid-infrared emission, which has unique applications in many fields. However, due to the immature manufacturing technique of soft glass fibers and the limited types of doped rear-earth, laser power enhancing and wavelength expansion beyond 4 μm are greatly restricted. Gas-filled hollow-core fibers (HCFs) have been proved to be an effective way to generate mid-infrared emission. We previously demonstrated a continuous-wave 4.3 μm fiber source with power of 82 mW in CO2-filled HCFs. Here, the maximum output power is increased to 557 mW, and laser wavelengths densely step-tunable from 4276 to 4428 nm including 46 lines have been demonstrated. The output spectrum and power properties with gas pressure and pump power are investigated in detail. In addition, the influence of buffer gases on laser characteristics is studied experimentally for the first time. This work provides significant guidance for the development of high-power tunable mid-infrared fiber gas lasers. [ABSTRACT FROM AUTHOR]

The selective generation of laser transverse modes by gain regulation with a digital micromirror device (DMD) is presented in this letter. The gain regulation in laser medium is adjusted by the switch of the patterns loaded on DMD. Structured pump beam patterns can be obtained after the reflection of the loaded patterns on DMD, and then it’s defocused into a microchip laser medium by a short focal lens, so that the pump patterns can be transferred to the gain medium to regulate the gain distribution. Corresponding structured laser beams can be generated by this laser system. The laser beam pattern can be regulated easily and quickly, by switching the loaded patterns on DMD. Through this method, we show a simple and flexible laser system to generate on-demand laser beam patterns. [ABSTRACT FROM AUTHOR]

Laser excitation in silicon from femto- to pico-second time scales is studied. We assume the three-temperature model which describes the dynamics of the distinct quasi-temperatures for electrons, holes, and lattice. Numerical results for damage threshold reproduce the experimental results not only quantitatively, but qualitatively as well, showing dependence on laser pulse duration. Comparison with experimental data suggests that electron emission and thermal melting are both responsible for damage in silicon. We found that electronâ€"phonon relaxation time has a significant effect on pulse duration dependence of electron emission. [ABSTRACT FROM AUTHOR]

A compact random fiber laser based on a short artificial Rayleigh reflector and heavily-doped Er fibers (custom-made and commercial as a reference) has been proposed, characterized and optimized in terms of efficiency, linewidth and noise level. A 10-cm artificial Rayleigh reflector with mean scattering level of +41.3 dB/mm relative to the natural Rayleigh scattering of the host fiber and low insertion loss level (∼0.05 dB/cm at 1535 nm) was fabricated using a femtosecond direct writing technique. Its implementation as a distributed output mirror in a half-open cavity of a 980-nm diode pumped Er-doped fiber laser results in random lasing at 1535 nm in single- and few-mode regimes with power up to 100 mW, slope efficiency up to 16.5%, and signal-to-noise ratio up to 60 dB. A single-frequency regime with ∼10 KHz linewidth was observed at output power up to 2.5 mW. Tunability potential of such random lasers is also demonstrated. [ABSTRACT FROM AUTHOR]

The role of a HfO2 or ZrO2 interlayer as a thermal bridge between a $\beta $ -Ga2O3 channel and a sapphire substrate was investigated using a $\beta $ -Ga2O3 nano-membrane FET as a test vehicle. A 35% less channel temperature increase was observed when a thin HfO2 or ZrO2 interlayer was inserted between the $\beta $ -Ga2O3 channel and the sapphire substrate compared to devices without interlayers. Phonon density of states (PDOS) mismatch can explain the improvement of the thermal boundary conductance (TBC). In the acoustic region, the PDOS of HfO2 or ZrO2 has about a 700% larger overlap area with the PDOS of $\beta $ -Ga2O3 compared to the PDOS of sapphire. This suggests that the insertion of a thermal bridge interlayer can provide a potential solution to the low thermal conductivity of $\beta $ -Ga2O3 and the self-heating effect of $\beta $ -Ga2O3-based FETs. [ABSTRACT FROM AUTHOR]

A dispersion-managed, figure-of-9, mode-locked ultrafast Yb-doped fiber laser is presented in this letter. The laser cavity employs a chirped fiber Bragg grating with a proper anomalous dispersion for intra-cavity dispersion compensation. The laser with large normal net dispersion delivers an output with maximum average power of 20 mW and pulse duration of 5.50 ps at the repetition rate of 39.1 MHz, and the pulse can be dechirped to 228 fs. While net dispersion of cavity is very close to zero, the laser delivers an output with an average power of 12 mW at the repetition rate of 47.3 MHz, and the pulse duration is 1.86 ps, which can be dechirped to 175 fs. The whole cavity is very compact and environmentally stable, for its all-polarization-maintaining and all-fiber structure. [ABSTRACT FROM AUTHOR]