Μm Laser Research Articles

Continous-wave and passively Q-switched laser at 1.36 µm of a Nd3+-doped phosphate fiber with a Yb3+-doped inner cladding

All-fiber continuous-wave (CW) and passively Q-switched lasers at 1.36 µm (4F3/2 → 4I13/2) by a Nd3+-doped double cladding phosphate fiber are demonstrated for the first time, to the best of our knowledge. To suppress the competitive 0.9 and 1.05 µm emission, the Yb3+ ions are intentionally introduced into the inner cladding of this Nd3+-doped fiber. CW laser at 1.36 µm with a signal-to-noise ratio over 50 dB is realized by using two fiber-type dielectric films as cavity mirrors. A 4.0% CW laser efficiency is obtained when the Nd3+-doped fiber length is 33 mm. The emission at 0.9 and 1.05 µm is well-suppressed, and no parasitic laser is observed. Taking a commercial semiconductor saturable absorber (SA) mirror as the SA, the compact 1.36-µm Q-switched laser is demonstrated, and the repetition rate of output pulses can be tuned from 230 to 522 kHz with a narrowest pulse duration of 152 ns. Our results may provide a promising way to realize 1.3 µm laser oscillation in Nd3+-doped fibers.

Enhanced the quantum efficiency of Tm3+ ∼2 μm laser in crystal through an energy transfer process of 3H5 level

The concentration dependence of the fluorescence and lifetime evolutions of states relevant to three near-infrared emission bands were measured and analyzed for Tm:SrF2 crystals. The fast quenching of ∼1.2 μm fluorescence (3H5) was observed as the Tm concentration increased. The cross-relaxation and multi-phonon relaxation processes between Tm3+ ions cannot explain this phenomenon. Through spectral and rate-equation analysis, two possible energy transfer mechanisms, cross-relaxation from the 3H5 level and cooperative energy transfer within Tm3+ clusters, are proposed. And based on the new modified model, the quantum efficiency of the Tm ∼2 μm lasers could surpass the traditional 200% limit. This new energy transfer has the potential for exceptionally high efficiency excitation of Tm-doped laser materials.

High beam quality and high peak power 1.6 µm deuterium Raman laser.

In this work, a 1.67 µm laser was generated in the pressurized deuterium pumped by a pulsed 1064 nm laser via the stimulated vibration + rotation Raman scattering (SV-RRS). By the optimization of the deuterium pressure, focal length, and polarization of the pump laser, a 66.2 mJ Raman laser was achieved with the configuration of 1.7 MPa deuterium pressure, 2245 mm focal length, and 220 mJ circularly polarized pump laser. Correspondingly, the photon conversion efficiency was 47.8%, the energy conversion efficiency was 30.5%, the pulse width was 5.4 ns, and the maximum peak power was 12.3 MW. In addition, SV-RRS was found to improve beam quality significantly: from Mx 2 = 2.67 and My 2 = 3.07 for the pump laser to Mx 2 = 1.42 and My 2 = 1.53 for the 1.67 µm Raman laser.

Highly efficient Tm-fiber laser resonantly pumped by a 1.7 µm laser diode

A CW laser diode emitting at 1.7 µm was used to unidirectionally pump a thulium-doped fiber laser. A cladding-pumped fiber laser resonator consisted of a dichroic (high reflectivity at 2 µm, high transparency at 1.7 µm) free-space plane mirror, placed between two lenses used to collimate and to focus the pumping radiation, and Fresnel reflection of an active fiber end that serves as an output coupler. For an absorbed power of 11.5 W, an output power of 5.2 W was achieved at a wavelength 1950 nm with a slope efficiency of 70%. The goal of our work is to attract attention to the possibility of pumping thulium fiber lasers resonantly using laser diodes that are already readily available today. Thanks to resonant pumping, compared to cross-relaxation-assisted pumping at 0.8 µm, higher efficiency and lower heat generation can be achieved, which can help to reach high mean powers from thulium fiber lasers. An important fact is that both the generated laser radiation and pumping radiation belong to the eye-safe spectral region, which reduces the risk of vision damage.

High-pulse-energy ultrafast 3 µm laser generation through OPG/DFG in PPMgLN

Abstract We report high-pulse-energy ultrafast 3 µm laser generation through optical parametric generation/difference frequency generation (OPG/DFG) in periodically poled magnesium-oxide-doped lithium niobate (PPMgLN). A commercial 1030 nm femtosecond laser is applied as the pump light and a homemade broadband nanosecond pulse laser around 1580 nm is used as the signal light in DFG. The broadband 1580 nm laser has a master oscillator power amplifier (MOPA) structure with a directly modulated superluminescent light-emitting diode (SLED) as the pulse seed and three stages of Er/Yb fiber amplifiers to lift its average power. A portion of the 1030 nm output pulse is converted to an electronic pulse via a pin detector, which is used as the trigger signal of the SLED driving circuit to ensure synchronization between the signal and the 1030 nm pump pulse. When injecting 2.12 W pump light into the PPMgLN, a broadband mid-infrared (MIR) output of 280 mW can be achieved directly through OPG with a center wavelength around 2.94 μm, a pulse width of 1.38 ps and a pulse repetition frequency of 500 kHz. The corresponding MIR pulse energy is 0.56 µJ. When injecting 2.62 W signal light simultaneously, a MIR output of 300 mW is achieved through the DFG process at the same pulse repetition frequency, corresponding to a pulse energy of 0.6 µJ. The conversion efficiency of the ultrafast pump laser to MIR reaches 14.1%. This high-pulse-energy 3 μm ultrafast laser has great prospects for applications in biological tissue ablation.

2.8 μm Laser Realized on a Novel Er:LuYAP Crystal End-Pumped by a 969 nm LD

2.8 μm Laser Realized on a Novel Er:LuYAP Crystal End-Pumped by a 969 nm LD

High power continuous-wave, Q-switched, and quasi-continuous-wave operation of a diode-pumped Tm,Ho:YAG laser oscillator at 2.09 μm

A high-power diode-pumped 2.09 μm Tm,Ho:YAG laser oscillator with multi-regime operation is demonstrated. In the continuous-wave (CW) regime, it delivers 44.68 W output power with M2 = 3.47, yielding a record-high brightness of 87.57 MW/cm2·sr. In the Q-switched mode, stable laser performance across pulse repetition frequencies (PRFs) from 1 kHz to 4 kHz is achieved. At a PRF of 1 kHz, single pulse energy reaches 22.85 mJ with a pulse width of 443.4 ns and M2 = 3.50. In the quasi-continuous-wave (QCW) operation, a pulse energy of 31.85 mJ is obtained at 200 Hz with a 370 μs pulse width and M2 = 4.49. These pulse energies are the highest reported to date for Tm-Ho co-doped laser oscillators at high PRF. This also marks the first demonstration of a versatile 2 μm laser that can operate at room temperature while delivering high-energy, high-repetition-rate pulses in both nanosecond and microsecond durations within a single device, making it highly appealing for scientific and industrial applications.

Laser microwelding of NiTi/PtIr alloys with laser beam offset

The NiTi and PtIr alloy joint has been employed in biomedical devices to combine the superelasticity of NiTi alloy with the X-ray visibility of PtIr alloy. Laser microwelding is usually used for the joints, but there is a risk of forming brittle intermetallic compounds (e.g., Ni3Ti, Ti2Ni, and Ti3Pt) in the fusion zone (FZ), which could deteriorate joint strength. In this study, laser beam offset (laser offset) was implemented for a butt joint of Ni-49.8 at.% Ti and Pt-10.0 at.% Ir alloy wires to control the intermetallic compound formation in the FZ. Welding with 300 μm laser offset on the NiTi side achieved 2.3 times higher joint breaking stress and 13.0 times higher joint breaking strain than welding without laser offset. The joint breaking stress and strain were enhanced from 221 MPa and 0.9% to 502 MPa and 11.7% by 300 μm laser offset on the NiTi side, respectively. In the absence of laser offset, the dissolution of Pt and Ir into the FZ facilitated the M3Ti (M = Ni, Pt, Ir) formation in the FZ, resulting in crack propagation within the M3Ti. In contrast, the 300 μm offset on the NiTi side inhibited the M3Ti formation by mitigating Pt and Ir dissolution into the FZ. Laser offset on the NiTi side can be an attractive option to enhance the strength and ductility of NiTi and PtIr butt joints.

Influence of the magnetic field on the emission of hot electrons and ions from ablative plasma produced from a disc-coil target irradiated by the 3rd harmonic of the PALS iodine laser

Abstract Experimental and theoretical study of plasma processes affected by strong laser generated magnetic fields is reported. The PALS laser system operating at 3ω (438.5 nm) delivered intensities up to 1×1016 W/cm2 on targets. By using a special target system consisting of a Cu foil connected to a sub-mm coil, magnetic fields up to the level of 10 T were generated. This is 1.4 times higher than the field generated with a 1.315 μm (1ω) laser beam at a comparable intensity. We found that these fields were sufficiently strong to modify plasma blow-off from the foil which resulted in the changed expansion dynamics and increased energy of hot electrons by 20-40% compared to the plasma unaffected by the magnetic field. To obtain complementary experimental data, a complex diagnostic system was used enabling the visualization of the plasma expansion process both in visible light (3-frame composite interferometry) and in the soft X-ray region (4-frame pinhole X-ray camera) together with measurements of the hot electron parameters using two-dimensional imaging of the Kα line emission from the Cu target and electron spectroscopy. Experimental data obtained from the angular distribution of electron energy spectra were used for three-dimensional (3D3V) numerical PIC simulations using a modified EPOCH code. By including interactions between ions, protons, hot and thermal electrons in forward and backward propagating particles, the effects of the magnetic field on the flux of hot electrons were visualized and compared with the experiment. The PIC simulation confirmed that the interaction of the hot electron flux with the magnetic field generated by the target-coil system leads to an increased flux energy. However, this increase is accompanied by increased complexity of the spatial structure and heterogeneity of the flux as well as its angular divergence.

Mechanoluminescence and Optically Stimulated Antistokes Luminescence of Composites Based on Epoxy Resin and Strontium Aluminate Phosphors SrAl<sub>2</sub>O<sub>4</sub>:Eu<sup>2+</sup>,Dy<sup>3+</sup> and Sr<sub>4</sub>Al<sub>14</sub>O<sub>25</sub>:Eu<sup>2+</sup>, Dy<sup>3+</sup>

Composite mechanoluminescent materials (composites) based on epoxy resin transparent in the visible range of spectrum and fine-dispersed powders of mechanoluminescent phosphors SrAl2O4:Eu2+, Dy3+ and Sr4Al14O25:Eu2+, Dy3+ were obtained. The mechanoluminescence and photoluminescence spectra of composites under the combined influence of short-wave (λ = 405 nm) and long-wave (λ = 1.06 µm) laser radiation were studied. The attenuation of optically stimulated antistokes luminescence of the composite under the influence of a sequence of pulses of longwave laser radiation was investigated. The composite was pre-irradiated with shortwave laser radiation. The obtained composite was used to visualize heat propagation and thermal deformations in metal plates arising under the action of powerful laser pulses and distribution of deformations under mechanical impact. For this purpose, a thin layer of the composite was applied to the surface of the materials under study. The composite had good adhesion to the surface of the materials and a high yield of mechanoluminescence, which allowed to visualize the distribution of temperature and surface deformations with a good spatial and temporal resolution.

Assessment of Weld Microstructure Through Sound Velocity Measurements for Power Plant Applications

This research study employed an immersion-based micro-resolution ultrasonic velocity measurement technique (MUVT) to evaluate Grade 91 (9Cr-1Mo-V) steel welds. This process utilized a 20 MHz focused ultrasonic beam with a spot size of 250 µm, a 6 µm laser vibrometer spot size for detection, and an automated 3-axis raster scanner to accurately collect ultrasonic velocity data from two Grade 91 steel welds fabricated using cold metal transfer (CMT) and flux-cored arc welding (FCAW) processes. By analyzing the MUVT data, the Poisson’s ratio (υ) and modulus of elasticity (E), which are important mechanical properties for weldments, were calculated. The correlation between mechanical properties and ultrasonic velocity was examined. The results indicated that longitudinal ultrasonic velocity could effectively identify base metal, heat-affected zone (HAZ), and weld metal areas, showing a strong correlation with hardness. In particular, the distinctive V-shaped dip in velocity and hardness data across the HAZ areas of both samples highlighted changes in the microstructure of creep strength–enhanced ferritic steel welds. Importantly, the immersion-based MUVT demonstrated high accuracy in small sections of the weld, surpassing the conventional contact ultrasonic testing method in spatial resolution detection.

Lasing at 2.1 µm pumped by a simultaneous-gain clad laser.

We obtained lasers based on the simultaneous-gain clad pump laser in a fluorotellurite fiber. Using a secondary suction method, we prepared a fluorotellurite double-clad preform with a Ho3+-doped core surrounded by a Tm3+-doped inner cladding, which we then drew into fibers. Tm3+ ions generate a 1.94 µm laser by pumping the inner cladding with a 1570 nm fiber laser. This is followed by further pumping of the Ho3+-doped core, and a 2.06 µm laser is obtained. Our results validate cladding simultaneous-gain feasibility of producing core lasers in a fluorotellurite fiber.

Effects of “blue” (λ = 450 nm) and pulsed periodic CO2 (λ = 10.6 μm) laser light at the skin of laboratory animals. A comparative experimental study

Effects of “blue” (λ = 450 nm) and pulsed periodic CO2 (λ = 10.6 μm) laser light at the skin of laboratory animals. A comparative experimental study

Crystal growth and the enhanced 1.55 μm fluorescence emission in Ce3+, Yb3+, Er3+ Co-doped KBaCaY(MoO4)3 laser crystal

1.55 μm laser technology has been widely applied in many fields such as military, information and communications, and biomedical. With the continuous progress in these fields, the demand for new 1.55 μm laser gain media has become stronger. However, the small non-radiative transition probability and long fluorescence lifetime between the 4I11/2 and 4I13/2 energy levels of Er3+ ions lead to up-conversion loss, which in turn reduces the luminescence efficiency in the 1.55 μm band. To address this problem, this paper introduces a novel Yb3+, Er3+ and Ce3+ co-doped KBa0.94Ca0.06Y(MoO4)3 crystal and explores the relationship between its structure and spectral properties. By doping Ce3+ ions, the non-radiative transition probability between the 4I11/2 and 4I13/2 energy levels of Er3+ ions is effectively increased, which significantly enhances the emission intensity of Er3+ ions in the 1.55 μm band. Meanwhile, the near-infrared luminescence mechanism of Er3+ ions and its complex competition with up-conversion and mid-infrared luminescence are elaborated in detail. In addition, the doping of Ce3+ ions also significantly enhances the energy transfer efficiency between Yb and Er, from 39.6 % to 94 %. At a Ce3+ ion concentration of 4 mol%, the crystals exhibit optimal emission intensities, indicating their great potential as laser gain media. The research presented here not only provides a comprehensive analysis of the spectral properties of the new laser gain material but also contributes to the advancement of all-solid-state laser gain media suitable for the 1.5 μm spectral range.

A 1.55 μm laser gain medium based on Yb3+ and Er3+ co-doped KBa0.94Ca0.06Y(MoO4)3 crystal with in-situ operating temperature self-monitoring capability

The 1.55 μm laser technology is widely applied in military, information communication, biomedicine and other fields. With the deepening development of these application areas, the demand for novel 1.55 μm laser gain media is becoming increasingly urgent. This study reports a novel Yb3+, Er3+ co-doped KBa0.94Ca0.06Y(MoO4)3 (KBCYM) crystal. In this crystal, Yb3+ serves as a sensitizer, significantly enhancing the emission intensity of Er3+ in both visible and near-infrared bands. Notably, when the concentration of Yb3+ reaches 6 mol%, the emission intensity peaks at 1.55 μm. Optical cross-section calculations reveal that the crystal exhibits a low laser pumping threshold at this concentration, demonstrating its potential as a laser gain medium. However, the crystal inevitably generates thermal effects during operation, which may adversely affect its performance. Therefore, real-time monitoring of the operating temperature is crucial. The thermal stability of the crystal was evaluated by measuring the temperature dependence of its luminescence intensity in the near-infrared band. Remarkably, even when the temperature rises to 553 K, the emission intensity at 1.55 μm only decreases by 10.9%. Additionally, the temperature sensing performance was evaluated using fluorescence intensity ratio techniques, yielding absolute and relative sensitivities of 0.00981 K–1 at 453 K and 1.32%/K at 303 K, respectively, highlighting its potential for optical temperature sensing. Finally, through leveraging the unique properties of Yb3+, Er3+: KBCYM crystals, we successfully developed 1.55 μm luminescent optical devices with practical applications. These devices not only exhibit efficient luminescent performance, but also possess a self-temperature measurement function, opening up new avenues for the further development of laser technology.

2.7μm luminescence and structural properties of Er3+-doped fluorotellurate glass

In this paper, the thermal properties and internal structures of fluorotellurate glasses with different concentrations of TeO2 were studied. Glass samples with a concentration of 30mol% TeO2 were doped with different concentrations of Er3+ (1,2, 3,3.5,4,4.5,5mol%) and their luminescence characteristics were analyzed. The fluorotellurate glass possess high infrared transmittance (93 %), thermal stability (ΔT>110 °C), and low phonon energy (821 cm−1). Er3+ doped fluorotellurate glass exhibits high fluorescence lifetime of 4I11/2 level (1.59 ms), large emission cross-section (5.98 × 10−21cm2), and achieves a quantum efficiency of up to 30 %. These experimental findings suggest promising prospects for the utilization of Er3+ doped fluorotellurate glass in 2.7 μm laser applications.

5.3 W/265 μJ Mid-IR All-Fiber Er3+:ZBLAN Gain-Switched Laser Based on Dielectric Fiber Mirror and Fiber-Tip Protection

We report a 2.8 μm all-fiber high-power and high-energy gain-switched Er3+:ZBLAN laser based on dielectric fiber mirror and fiber-tip protection. The fiber pigtail mirror, specifically designed for dichroic operation (i.e., anti-reflection at 976 nm pump wavelength and high-reflection around 2.8 μm laser wavelength), shows high damage density of >10 MW/cm2. An anti-reflection protective film is coated on the input tip of Er3+:ZBLAN fiber and an AlF3 endcap is spliced to the output tip of Er3+:ZBLAN fiber for mitigating the fiber-tip photodegradation and high-power catastrophic failure at 2.8 μm. The compact all-fiber cavity is formed by efficiently connecting the Er3+:ZBLAN fiber with dielectric fiber mirror using the standard FC/PC fiber adaptor. When the 976 nm pump operates in pulsed regime, the all-fiber mid-infrared gain-switched laser can be attained with two states of single-pulse and pulse-burst output. The extracted maximum pulse energy is 4.8 μJ in the single-pulse state, and the shortest pulse width is 426 ns. The pulse-burst mode can generate a maximum average power of 5.291 W and burst energy of 264.55 μJ. This work may offer a promising way to realize the low-cost, all-fiber, high-power and high-energy gain-switched laser at MIR wavelengths.

Enhancing 2.7 µm emission of Er3+ in bismuth glass by introducing ZnO

In recent years, 2.7 μm lasers have attracted the attention of many researchers due to their wide application in military, medical, aerospace and other fields. This study investigates the gain effect of ZnO on Er3+-doped bismuthate glasses by partially replacing GeO2 in the glass with ZnO. It is found that under 980 nm pump excitation, with the increase of ZnO, the emission of Er3+ at 1.5 μm and 2.7 μm was enhanced. This result is consistent with the changing trend of J-O parameter Ω2. All these results confirmed that the introduction of ZnO into bismuthate glasses is a reasonable and effective method to enhance the mid-infrared 2.7 μm emission in Er3+-doped bismuthate glasses. Therefore, the current research indicates that an appropriate amount of ZnO in Er3+-doped bismuthate glasses is a suitable materials for 2.7 um fiber lasers.

Nested hollow-core anti-resonant fiber with elliptical cladding for 2 µm laser transmission

In this work, a nested hollow-core anti-resonant fiber (HC-ARF) with an elliptical cladding for high-power lasers for 2 µm laser transmission was proposed and theoretically investigated. The dual-layer elliptical tubes nested within the fiber enable the low-loss single-mode transmission. The finite element method (FEM) was employed to analyze and optimize the structure of fiber, with a total loss of less than 5 × 10−4 dB/m across the wavelength range of 1920nm to 2040nm. An extremely low loss of 1.22 × 10−5 dB/m at 1948nm was realized. A high-order mode extinction ratio (HOMER) exceeding 3 × 104 was maintained across a significant bandwidth and a size tolerance ratio under 15%. Furthermore, a low loss of 5 × 10−5 dB/m at 1948nm with a bending radius over 15 cm was obtained, indicating high bending resistance. It was demonstrated that the proposed fiber has exceptional transmission performance for 2 µm laser transmission.

Broadband rapid-scanning phase-modulated Fourier transform electronic spectroscopy

We present a phase-modulated approach for ultrabroadband Fourier transform electronic spectroscopy. To overcome the bandwidth limitations and spatial chirp introduced by acousto-optic modulators (AOMs), pulses from a 1 µm laser are modulated using AOMs prior to continuum generation. This phase modulation is transferred to the continuum generated in a yttrium aluminum garnet crystal. Separately generated phase-modulated continua in two arms of a Mach-Zehnder interferometer interfere with the difference of their modulation frequencies, enabling physical under-sampling of the signal and the suppression of low-frequency noise. By interferometrically tracking the relative time delay of the continua, we perform continuous, rapid-scanning Fourier transform electronic spectroscopy with a high signal-to-noise ratio and spectral resolution. As proof of principle, we measure the linear absorption and fluorescence excitation spectra of a laser dye and various biological samples.