Solid-state Laser Research Articles

Growth, optical and thermal properties of YbxHo1-xCa4O(BO3)3 crystals

YbxHo1-xCa4O(BO3)3 (Yb:HoCOB, x = 0, 0.1, 0.2, 0.3) crystals were grown by the Bridgman method for the first time. The crystal structure, rocking curve, transmission spectra, absorption spectra, band structure and thermal properties of Yb:HoCOB were characterized in detail. The maximum half peak width (FMHW) of Yb0.1Ho0.9COB and Yb0.2Ho0.8COB is 26.7″ and 23.8″, respectively, and the effective segregation coefficient is greater than 0.9. In addition, the transmittance of Yb:HoCOB is 88 %. New absorption peaks are introduced by doping Yb3+ at 850–1000 nm. The UV absorption cut-off edge of Yb:HoCOB is red-shifted with increasing Yb3+ doping. The thermal diffusivity and thermal conductivity of Yb:HoCOB decrease with increasing temperature. The specific heat increases with the increasing temperature and finally approaches a constant value. The specific heat of Yb:HoCOB crystal are above 0.670 J/gK at room temperature. Yb:HoCOB with good crystallization quality, high transmittance and high specific heat has the application potential in laser frequency and QPCPA. This work provides a useful exploration for the study of nonlinear optical materials in solid state lasers.

Quasi-three-level laser pumped Yb:GdCOB tunable laser from 1030 to 1036 nm

We report a quasi-three-level laser pumped Ca4GdO(BO3)3 (Yb:GdCOB) tunable laser based on the transition from the 2 F 5/2 level to the 2 F 7/2 level. By adjusting the 902 nm pump power, a continuous waves Yb:GdCOB laser was obtained with the near-infrared wavelengths shifting from 1030 nm to 1036 nm. The highest tuning power of 2.5 W was achieved with a slope efficiency of 19.9%. To our knowledge, it is the first tunable Yb:GdCOB laser to be realized by adjusting the pump power. This work provides a novel method to generate tunable solid-state lasers with a compact and simple structure.

Stability improvement of high-power semiconductor laser diode regulators used in infrared solid-state laser applications

Stability improvement of high-power semiconductor laser diode regulators used in infrared solid-state laser applications

First-Principles Investigations of the Electronic Structure and Mechanical Characteristics of Nd3+-Doped YAlO3 Crystals

Near-infrared laser radiation based on Nd3+-doped yttrium ortho-aluminate (Nd:YAlO3, Nd:YAP) has garnered significant interest regarding solid-state lasers. Nevertheless, the crystal microstructures and electronic characteristics of Nd:YAP are still unclear, and the unique physical properties underlying its enormous applications require clarification. In this study, we conducted first-principles calculations at the atomic level to explore the electronic properties and mechanical characteristics of both pure YAP and Nd3+-doped YAP. The results suggest that the substitution of the Y3+ ion site with the Nd3+ impurity ion induces slight structural distortion in the YAP crystal lattice. An impurity band emerges between the original conduction band and the valence band, attributed to the 4f orbital of the Nd3+ ion, exerting a substantial influence on the narrowing of the band gap. Through an analysis of the mechanical characteristics of both pure YAP and Nd:YAP, we conclude that the incorporation of Nd3+ atoms leads to a reduction in the mechanical properties of YAP to a certain extent. Our study can serve as a foundational data source for investigations into material performance, especially for the application of Nd:YAP in solid-state laser systems.

Engineering of Solid-State Nanoporous Laser through Dendrimer-Encapsulated Fluorophores.

Dendrimers─nanosized macromolecules that can function as hosts for encapsulation of guest molecules─provide new avenues to engineer gain media for lasing systems. In this context, this study investigates the interplay between the geometric features of a model porous scattering medium, nanoporous anodic alumina (NAA), and the chemical features of a model fluorophore-dendrimer encapsulation system to maximize random lasing. The inner surface of the NAA platforms is functionalized with fluorophore molecules encapsulated within dendrimers via an electrostatic interaction. The resulting solid-state composite structures emit well-resolved, intense random lasing when subjected to optical pumping. By engineering fluorophore-dendrimer and geometric features of scattering medium, we can precisely tune the characteristics of random lasing emissions. It is found that lasing structures with low porosity and thickness functionalized with fluorophore molecules encapsulated in second-generation dendrimers provide the best platforms for lasing generation, resulting in a strongly polarized laser at ∼594 nm that has a high quality-gain product of ∼1588 au, a polarization quality of ∼0.86, and a lasing threshold of ∼0.05 mJ pulse-1. Comparative analysis indicates that dendrimers achieve 2.5 times better random lasing than conventional surfactants due to improved encapsulation and minimization of photobleaching. Our results reveal the importance of the fluorophore encapsulation method and design of scattering media in the engineering of random lasing platforms for applications in optical and optoelectrical systems.

Demonstration of stable, long-term operation of a nanosecond pulsed DPSSL at 10 J, 100 Hz.

We report on stable, long-term operation of a diode-pumped solid-state laser (DPSSL) amplifying 15 ns pulses at 1029.5 nm wavelength to 10 J energy at 100 Hz pulse rate, corresponding to 1 kW average power, with 25.4% optical-to-optical efficiency. The laser was operated at this level for over 45 minutes (∼3 · 105 shots) in two separate runs with a rms energy stability of 1%. The laser was also operated at 7 J, 100 Hz for 4 hours (1.44 · 106 shots) with a rms long-term energy stability of 1% and no need for user intervention. To the best of our knowledge, this is the first time that long-term reliable amplification of a kW-class high energy nanosecond pulsed DPSSL at 100 Hz has been demonstrated.

The Impact of the Amorphous-to-Crystalline Transition on the Upconversion Luminescence in Er3+-Doped Ga2O3 Thin Films

Gallium oxide (Ga2O3) is an emerging wide bandgap semiconductor promising a wide range of important applications. However, mass production of high-quality crystalline Ga2O3 still suffers from limitations associated with poor reproducibility and low efficiency. Low-temperature-grown amorphous Ga2O3 demonstrates comparable performance with its crystalline counterparts. Lanthanide Er3+-doped Ga2O3 (Ga2O3: Er) possesses great potential for developing light-emitting devices, photodetectors, solid-state lasers, and optical waveguides. The host circumstance can exert a crystal field around the lanthanide dopants and strongly influence their photoluminescence properties. Here, we present a systematical study of the impact of amorphous-to-crystalline transition on the upconversion photoluminescence in Ga2O3: Er thin films. Through controlling the growth temperature of Ga2O3: Er films, the upconversion luminescence of crystalline Ga2O3: Er thin film is strongly enhanced over 100 times that of the amorphous Ga2O3: Er thin film. Moreover, the variation of photoluminescence reflects the amorphous-to-crystalline transformation of the Ga2O3: Er thin films. These results will aid further designs of favorable optoelectronic devices integrated with lanthanide-doped Ga2O3 thin films.

28.02 W LD side-pumped CW laser operated at 2.8 µm in YSGG/Er:YSGG/YSGG crystal.

We demonstrated a 978 nm laser diode (LD) side-pumped YSGG/Er:YSGG/YSGG composite crystal with a size of Ф 3 mm × 65 mm and continuous-wave (CW) mode. By optimizing resonator length and output mirror transmittance, a maximum output power of 28.02W is generated, corresponding to slope efficiency of 17.55% and optical-optical efficiency of 12.29%, respectively. The thermal focal lengths are obtained by resonator stability condition. The laser wavelength is centered near 2.8 µm. Moreover, the beam quality factors M x2/M y2 are fitted to be 8.14 and 7.35, respectively. The above results indicate that a high-performance 2.8µm CW laser can be achieved by LD side-pumped YSGG/Er:YSGG/YSGG composite crystal with excellent heat dissipation ability, which promotes effectively the development and applications of the mid-infrared solid-state lasers.

Double-Junction Cascaded GaAs-Based Broad-Area Diode Lasers with 132W Continuous Wave Output Power

Improving the output power and efficiency of broad-area diode lasers is a prerequisite for the further development of fiber lasers, solid-state laser industries, and direct semiconductor laser applications. At present, the large amount of Joule heat generated by large drive currents and limited wall-plug efficiency presents the largest challenge for improving these lasers. In this paper, a multi-junction cascade laser with low Joule heat generation is demonstrated, showing large power and conversion efficiency. We fabricated devices with different junction numbers and compared their output power. We present double-junction lasers emitting at ~915 nm with an emitter width of 500 μm, delivering 132.5 W continuous wave output power at 70 A, which is the highest power reported so far for any single-emitter laser. The power conversion efficiencies are 66.7% and 60%, at 100 W and 132 W, respectively.

30-100 kHz, 2 ns passively Q-switched laser for fast and efficient photoacoustic microscopy.

Actively Q-switched (AQS) fiber laser and solid-state laser (SSL) are widely used for photoacoustic microscopy (PAM). In contrast, passively Q-switched (PQS) SSL not only maintains most of the merits of AQS lasers, but also exhibits unique advantages, including the pulse width (PW), pulse repetition rate (PRR) tunability, wavelength, compactness, and cost. These advantages all benefit the PAM. However, there are few reports demonstrating the performance of PQS-SSL on PA imaging. Here, we demonstrate a compact PQS-SSL for fast and efficient PA imaging. The laser uniquely maintains a constant PW (~2 ns) and pulse energy (~3 μJ) during the PRR variation (30-100 kHz), which is valuable for preserving a stabilized imaging performance at different scanning rates. The PA imaging performance is compared by a resolution target and showcased by whole-body scanning of an embryonic zebrafish in vivo. The performance indicates that PQS-SSL is a promising candidate for PAM.

INFLUENCE OF SURFACTANT CONCENTRATION ON CHANGES IN THE PLANE OF POLARIZATION OF LIGHT WHEN PASSING THROUGH THE LCD MEDIUM

The effect of surfactants in the form of cetyltrimethyl ammonium bromide (CTAB) in nematic liquid crystal cells of type 5CB have been studied by the polarization-optical method. The relationship between the concentrations of the introduced surfactant and the angle of rotation of the polarization plane is established. The clear boundaries of the linear and elliptical polarization of the light transmitted through the cell are indicated, depending on the concentration of surface-active substances (surfactants). Possible applications of such materials in semiconductor and solid-state laser technology and display technologies are proposed.

Broadband near infrared emission of Er3+ ions doped fluorophosphate glasses for solid state laser applications

A series of glass compositions (P2O5 + Bi2O3 + Na2CO3 + SrF2 + xEr2O3) with different concentrations of erbium ions (Er3+) was synthesized using the melt quenching method and the samples were subjected to thorough characterization to explore their optical and structural properties. In order to ascertain the amorphous nature of the glass and acquire a deeper understanding of its chemical bonding, conventional methods of characterization, such as X-ray diffraction and Fourier transform infrared spectroscopy, were utilized. The Judd-Ofelt intensity parameters were computed using the absorption spectra of glasses doped with Er3+, providing vital information about the local environment and coordination of Er3+ ions in the glass matrix. Using the Judd-Ofelt intensity parameters and emission spectra to calculate the radiative parameters like total radiative transition probability (AT), radiative lifetime (τR) and radiative branching ratios for 4I13/2 → 4I15/2 transition. The McCumber theory is used to study absorption and emission cross-section for 4I13/2 → 4I15/2 transition. Prepared the PBNSEr05 glass sample suitable candidates for 1.53 μm solid state laser applications.

Structural and spectroscopic correlation in barium-boro-tellurite glass hosts: effects of Dy2O3 doping

In this study, a series of barium-boro-tellurite glass hosts with varying concentration of Dy2O3 doping (0 to 1.25 mol%) were made by melt-quenching method. A study was conducted to investigate how Dy2O3 dopants affect the physical and spectroscopic traits of glasses. Raw materials including barium oxide (BaO), tellurium dioxide (TeO2), boron oxide (B2O3), and dysprosium oxide (Dy2O3) were used to produce these glasses. XRD patterns of the samples showed a broad hump and absence of long-range periodic lattice arrangements, indicating their amorphous nature. The Raman spectral analyses displayed the various vibration modes where the most intense band caused by BaO vibrations at 300 cm-1 and 450 cm-1 corresponding to the symmetric stretching vibration mode of Te–O–Te intra-chain bridges. The peak at 750 cm-1 was due to TeO4 and Te-O-Te vibration modes. The value of optical band gap energy was decreased from 3.155 to 2.1894 eV and then increase at higher Dy2O3 level (0.75 to 1.25 mol%). At Dy3+ contents between 0.25 to 1.25 mol% seven absorption bands were observed at 390, 424, 452, 750, 797, 895 and 1092 nm due to the electronic transitions in Dy3+. The glass refractive indices were raised from 2.3563 to 2.6584 and then decreased at higher Dy2O3 contents which was mainly because of the generation of more bridging oxygen (BO) in the glass matrix. The value of glass electronic polarizability and oxide ions polarizability calculated using LorentzLorenz equation showed a decrease with the rise of Dy2O3 contents, which was ascribed to the presence of fewer non-bridging oxygen (NBO). The optical basicity of the proposed glass hosts was calculated using Duffy and Ingram equation which was decreased with the increase of doping contents. In addition, the optical transmission was increased and reflection loss was reduced with increasing Dy+3 levels. The value of metallization parameter below 1 proved the true amorphous nature of the prepared samples. All the glasses revealed blue and yellow photoluminescence emission peaks due to 4F9/2→ 6H15/2, and 4F9/2 →6H13/2 transitions in Dy3+, respectively. The proposed glass compositions may be beneficial for the advancement of solid-state lasers.

A Load-Adaptive Driving Method for a Quasi-Continuous-Wave Laser Diode.

A quasi-continuous-wave (QCW) laser diode (LD) driver is commonly used to drive diode bars and stacks designed specifically for QCW operations in solid-state lasers. Such drivers are optimized to deliver peak current and voltage pulses to LDs while maintaining low average power levels. As a result, they are widely used in laser processing devices and laser instruments. Traditional high-energy QCW LD drivers primarily use capacitors as energy storage components and pulsed constant-current sources with op-amps and power metal-oxide-semiconductor field-effect transistors (MOSFETs) as their core circuits for generating repeated constant-current pulses. The drawback of this type of driver is that the driver's output voltage needs to be manually adjusted according to the operating voltage of the load before use to maximize driver efficiency while providing a sufficient current. Another drawback is its inability to automatically adjust the output voltage to maintain high efficiency when the load changes during the driver operation. Drastic changes in the load can cause the driver to fail to function properly in extreme cases. Based on the above traditional circuit structure, this study designed a stability compensation circuit and realized a QCW LD driver for driving a GS20 diode stack with a maximum repetition rate of 100 Hz, a constant current of approximately 300 A, a load voltage of approximately 10 V, and a pulse width of approximately 300 μs. In particular, a high-efficiency, load-adaptive driving method was used with the MOSFETs in the critical saturation region (i.e., between the linear and saturated regions), controlling its power loss effectively while achieving maximum output current of the driver. The experiments demonstrated that the driver efficiency could be maintained at more than 80% when the load current varied from 50 to 300 A.

Structural and optical investigations of RE3+: Yb, Er, Sm, Nd, Ce-doped multi-functional silica glasses for photonic applications

The influence of various trivalent lanthanides was investigated in the silica phosphate multi-component glass matrix, synthesized by the sol-gel method. The prepared glasses were analyzed to explore the degree of bandwidth amplification for telecommunication systems, and the potentiality of lasing media and smart glass films. Alkaline earth metal ions of Ca2+ were effectuated as a glass modifier, mediating the formation of non-bridging oxygen with the glass formers, and imputing favorable structural attributes to the glasses for versatile applications. The bonding parameter derived from the average nephelauxetic ratio implies covalency around the rare earth ion sites in the Er3+ and Nd3+ doped systems, while the Sm3+ doped glass exhibits ionicity. In the silica-based glass matrix singly doped with Yb3+, the coexistence of Yb3+/Yb2+ ions was evidenced. Transitions across 4f14 and 4f135d levels of Yb2+, with an experimental lifetime of 45.8 ns would provide prospective pulsed yellow lasers, for non-invasive therapeutics. Er3+ doped glass evinced a large bandwidth of 93.775 nm at 1477 nm and a high quantum efficiency of 97%, favorable for O + E + S-band telecommunication networks. The transition corresponding to 4G5/2→6H7/2 of Sm3+ and 2G7/2→4I9/2 of Nd3+ is suggestive that the respective doped glasses could be devised into solid-state red and green laser sources. Novel near-infrared emission at 1476 nm was also evidenced in the Sm3+ and Nd3+ doped systems. Prominent absorption at 280 nm and complete transparency in the visible region observed in the Ce3+ mono-doped system make it ideal for smart glasses as UVB and UVC shielding films.

Enhancing fluorescence properties in transparent glass ceramics via optimized Gd2O3/Ga2O3 ratios and crystallization conditions

In this study, Gd2O3–Ga2O3-GeO2-Nd2O3 glasses and glass ceramics were synthesized, and their structural, thermal, and crystallization characteristics were analyzed. Our findings indicate that substituting Gd2O3 for Ga2O3 positively influences the enhancement of bridge oxygen content and network structure stability. Heat treatments at different temperatures showed no significant impact on the crystal phase type but did alter the crystallization rate. Optimal conditions were identified: a Gd2O3/Ga2O3 ratio of 0.6 facilitated the production of transparent glass ceramics containing a single-phase GdGaGe2O7 nano-crystal. Notably, the glass ceramic nucleated at 780 °C for 24 h and crystallized at 840 °C for 5 min exhibited superior performance. Despite a 6% reduction in transmission rate, the emission intensity at 1060 nm increased by 1.5 times. This material holds promise for various applications in solid-state lasers operating within the 1.06 μm region.

Laser frequency stabilization with the use of homodyne quadrature interferometers

Laser frequency stabilization is a crucial technique for precision metrology. We demonstrate laser frequency control using a compact, interferometric sensor, specially modified for sensitivity to laser frequency noise. This setup achieves a balance between compact size, ease of use, and affordability. We stabilize the laser frequency noise, of a low-cost solid-state laser, to 4.5 kHz Hz−1 at 1 Hz. The requirement for additional technology, and expense, is negated when identical, compact, interferometric sensors are deployed. The use of compact interferometric sensors is already a technology under investigation for integration into gravitational-wave observatories and out study enables wider applications by mitigating a fundamental noise source, inherent to their design.

Absorption Activity Investigation of Saturable Absorber for Dual Wavelengths in Laser Passive Q-Switching System

Objective: The absorption activity of saturable absorber material (Cr+4: YAG) for dual wavelengths (1.064 μm and 0.946 μm), simultaneously generated in same passive Q-switching system, has been investigated. Methods: This study utilized the mathematical model that was used in our previous study. Rung-Kutta—Fehelberge numerical method has been used to solve this mathematical model. Nd+3: YAG used as an effective medium and Cr+4: YAG used as a saturable absorber in the laser passive Q-switching optical system. Finding: When the population density of saturable absorber increases, the steady state of photons losses occurs at advancement time and the absorption activity reaches to optical bleaching state at advancement time also (it is occurring approximately at time 35 ns from the beginning of the time of pulse construction when the , while at , approximately at time 47 ns). Novelty: The absorption activity of saturable absorber material for a single wavelength of photons oscillating inside the passive Q-switch laser system received attention by some studies. This study verifies or investigates from the behavior of absorption activity of saturable absorber material when encounters photons with two wavelengths oscillating simultaneously inside the laser cavity in order to obtain high power of the pulses. Keywords: Laser, Passive Q­switching, laser, Dual wavelengths laser, Solid state lasers

In Vivo Imaging of Secondary Neurodegeneration Associated With Phosphatidylserine Externalization Along Axotomized Axons.

Axonal degeneration in acute and chronic disorders is well-characterized, comprising retrograde (proximal) and Wallerian (distal) degeneration, but the mechanism of propagation remains less understood. Laser injury with a diode-pumped solid-state 532nm laser was used to axotomize retinal ganglion cell axons. We used confocal in vivo imaging to demonstrate that phosphatidylserine externalization is a biomarker of early axonal degeneration after selective intraretinal axotomy. Quantitative dynamic analysis revealed that the rate of axonal degeneration was fastest within 40minutes, then decreased exponentially afterwards. Axonal degeneration was constrained within the same axotomized axonal bundles. Remarkably, axon degeneration arising from the site of injury induced a secondary degeneration of distal normal axons. Axonal degeneration in vivo is a progressive process associated with phosphatidylserine externalization, which can propagate not only along the axon but to adjacent uninjured axons. This finding has implications for acute and chronic neurodegenerative disorders associated with axonal injury.

Silicon photonics-based high-energy passively Q-switched laser

Chip-scale, high-energy optical pulse generation is becoming increasingly important as integrated optics expands into space and medical applications where miniaturization is needed. Q-switching of the laser cavity was historically the first technique to generate high-energy pulses, and typically such systems are in the realm of large bench-top solid-state lasers and fibre lasers, especially in the long wavelength range >1.8 µm, thanks to their large energy storage capacity. However, in integrated photonics, the very property of tight mode confinement that enables a small form factor becomes an impediment to high-energy applications owing to small optical mode cross-sections. Here we demonstrate a high-energy silicon photonics-based passively Q-switched laser with a compact footprint using a rare-earth gain-based large-mode-area waveguide. We demonstrate high on-chip output pulse energies of >150 nJ and 250 ns pulse duration in a single transverse fundamental mode in the retina-safe spectral region (1.9 µm), with a slope efficiency of ~40% in a footprint of ~9 mm2. The high-energy pulse generation demonstrated in this work is comparable to or in many cases exceeds that of Q-switched fibre lasers. This bodes well for field applications in medicine and space.