Laser Output Research Articles

In Situ Preparation of Thin-Film Q-Switches Based on Vanadium Dioxide for Pulsed Fiber Lasers

In the presented work, erbium fiber lasers operating in the pulsed mode with a nonlinear element containing a vanadium oxide saturable absorber are demonstrated. The structure of the saturable absorber is based on a segment of thinned silica fiber coated with a thin-film vanadium oxide by the method of metalorganic chemical vapor deposition. A fiber laser scheme is demonstrated that allows controlling the transmission of the internal cavity of the resonator during laser generation and deposition of a thin film. We have demonstrated a method for obtaining and annealing nanocoatings with laser generation control. We controlled the laser output parameters directly during the synthesis of the saturable absorber material. Vanadium oxides obtained in the work demonstrated the Mott–Paierls phase transition practically at room temperature. In this work, the optical characteristics of the output radiation of a fiber laser with a saturable absorber were measured. At temperatures above 70 °C, the coatings demonstrate a passive Q-switch with a repetition rate of 38 kHz and a pulse duration of 3.8 μs. At temperatures below the phase transition, a short-term mode-locking mode occurs. The transmission jump at a wavelength of about 1350 nm during structural rearrangement was 24%. For comparison, VO2 nanopowder in a polydimethylsiloxane elastomer matrix was used as a saturable absorber material. The nanopowder modulator made it possible to obtain pulses with a frequency of 27 kHz and a duration of about 7.2 μs.

Direct generation of watt-level visible-near infrared dual-wavelength Pr3+:LiYF4 lasers pumped by blue laser diode

We report a watt-level visible-near-infrared (NIR) dual-wavelength Pr3+:LiYF4 (Pr:YLF) laser. This is the first report about the realization of visible-NIR dual-wavelength lasing in Pr:YLF crystal. The dual-wavelength lasers of 698 & 868 nm and 721 & 915 nm are directly realized without inserting any elements in the resonant cavity. The maximum output powers of the 698 & 868 nm and 721 & 915 nm dual-wavelength lasers are 1.31 W and 1.74 W, corresponding to slope efficiencies of 25.7% and 23.8%, and laser output power stabilities of 1.18% and 1.21%, respectively. The successful realization of the watt-level high-performance visible-NIR dual-wavelength laser can provide practical applications in medical diagnostics, treatment, and laser precision detection.

Theoretical study on cascade Energy-transfer pumping heavily holmium-doped fluoroindate fiber laser at ∼ 4 μm with high-efficiency

In this article, we propose a cascade pumping scheme that employs 1.945 μm and 1.66 μm fiber laser as the pump sources to realize efficient laser emission at 3.92 μm in the commercially available heavily holmium-doped fluoroindate fibers. Compare to the conventional 888 nm laser diode, longer wavelength pump sources provide higher quantum efficiency, which is critical for the acquisition of high output power at a relatively low input pump power considering the low damage threshold of InF3 glass. Output performance is optimized by conducting detailed investigation on fiber length, output coupler mirror reflectivity and launched pump power. Simulation results show that when employing cladding pump at both 1.945 μm and 1.66 μm, a slope efficiency of 25 % can be achieved with a threshold of 1.6 W for the 1.66 μm pump source. This is attained using a 15 cm-long fiber under a pump power of 5 W at 1945 nm. Furthermore, the maximum optical-to-optical efficiency reaches 11.17 % when considering the total pump power. To our knowledge, the efficiency achieved in this study appears to surpass that of previous works. This research provides a novel approach and valuable guidance for efficient laser output at the important ∼ 3.9 μm wavelength region, for applications in various fields such as free-space communications, remote sensing and medical diagnostics.

High-precision 1.5 µm band tunable single-frequency fluoro-sulfo-phosphate fiber laser based on a self-injection locking scheme

In this paper, a high-precision 1.5 µm band tunable single-frequency Er3+/Yb3+ co-doped fluoro-sulfo-phosphate (EYFSP) fiber laser based on a self-injection locking scheme is experimentally demonstrated. A self-developed 4 cm long EYFSP fiber with a high gain coefficient (3.2–4.7 dB/cm) at the C-band serves as the gain medium for laser output. The single longitudinal mode (SLM) operation is realized via a 15 cm long commercial unpumped gain fiber and a self-injection locking scheme, while flexible wavelength tuning is controlled by a fiber Fabry–Perot tunable filter (FFP-TF). The laser wavelength is tuned from 1528.08 to 1555.55 nm, with a tuning precision of up to 10–18 pm and a tuning speed of 30 nm/s. Throughout the entire tuning range of 27.47 nm, the measured laser linewidth is less than 1.3 kHz, the relative intensity noise remains below −140dB/Hz at frequencies above 3 MHz, and the power fluctuation is as low as 1% over a measurement period of 2 h. These results demonstrate that the high-precision 1.5 µm band tunable single-frequency EYFSP fiber laser is a promising candidate for future coherent optical communication systems and optical fiber sensing.

Analysis of output characteristics of LD end-pumped 2.94 μm continuous-wave Er:YAG laser

Abstract Considering self-saturation effect and thermal effect, a detailed theoretical analysis of the output characteristics of the 2.94 μm continuous-wave (CW) Er:YAG laser with a 10 mm long 50 at.% Er:YAG crystal end-pumped by a 976 nm LD is carried out by solving transient rate equations and heat conduction equations. It is shown that there is a minimum pump power threshold of 0.27 W for the 2.94 μm CW Er:YAG laser. The main factor which limits the significant increase of pump power is the thermal damage risk of the crystal’s pump end-face coating. To minimize the risk, the CW operating temperature of the pump end-face coating is set to be no higher than 200 °C, and therefore the value of the pump beam waist radius is limited to 40 μm ⩽ w 0 ⩽ 490 μm. Within the range, a maximum 2.94 μm CW laser output power of 4.03 W is achieved with a pump beam waist radius of 100 μm. By bonding a 2.5 mm long YAG crystal at the pump-end of the Er:YAG crystal, the CW operating temperature of the pump end-face coating is reduced to the room temperature of 20 °C. Under this condition, the limiting factor for a substantial increase of pump power is the thermal damage risk induced by large interior thermal stress of the Er:YAG crystal. Assuming the interior thermal stress of the CW operating Er:YAG crystal is less than 341 MPa according to the material characteristics, the pump power can be increased by increasing the pump beam waist radius. When the beam waist radius is 430 μm, a maximum 2.94 μm CW laser output power of 38.7 W is obtained. Compared with the unbonded condition, the output power level of the 2.94 μm CW Er:YAG laser is promoted.

Research on LD-pumped single-frequency laser based on twisted-mode-cavity and RVBG

Abstract Single-frequency lasers have the advantages of good spectral purity, high peak spectral density, long coherence distance and low phase noise. They are widely used in fields such as laser spectroscopy, laser lidar, sodium guide stars, coherent optical communication and high-resolution measurement. We designed an all-solid-state single-frequency laser based on twisted-mode-cavity (TMC) structure and used a reflective volume Bragg grating (RVBG) to replace the ordinary output mirror. Through the composite mode selection effect of the twisted-mode-cavity and RVBG, the occurrence of multi-longitudinal mode oscillation is eliminated successfully, and precise optical frequency selection is achieved. When the pump power reached 88.0 W, the output power was 1.6 W, allowing for stable single-frequency laser operation at 1064.44 nm, with an output laser linewidth of 9.77 × 10−3 pm, the corresponding slope efficiency was 10.00%, and the light-to-light conversion efficiency was 1.82%. The power instability was less than 4.44% and the beam quality factor were M x 2 = 1.35 , M y 2 = 1.38 . Experimental results show that compared with using a RVBG or twisted-mode-cavity individually, the combination of the two methods can significantly compress the laser linewidth and achieve single-frequency laser output.

Bleaching effect of radiation-induced darkening in Yb3+-doped large mode area photonic crystal fiber based on deuterium and hydrogen loading.

We report the radiation-induced darkening (RD) effect caused by X-ray radiation and the bleaching effect caused by D2/H2/N2 loading in self-developed Yb3+-doped large mode-area photonic crystal fibers (LMA PCFs). The decrease in the slope efficiency caused by irradiation decays exponentially with an increase in the X-ray radiation doses, and the radiation-induced gain variation (RIGV) showed a linear decay trend with increasing irradiation doses. The slope efficiency of Yb3+-doped LMA PCF, which significantly degraded from 71.00% to 50.42% after 50 Gy irradiation, can be significantly restored after D2 loading to 97.21% of the slope efficiency of pristine fiber. However, the slope efficiency of the PCF loaded by H2 can be recovered to 88.54% that of the pristine. These results suggest that D2 loading has a more pronounced bleaching ability than H2, while N2 does not exhibit any bleaching effect. Based on the all-fiber modular amplification experiment, an average amplified output power of 41.4 W at the pump power of 62.3 W was achieved from Yb3+-doped LMA PCFs irradiated with 50 Gy followed by D2 loading. The slope efficiency (with respect to the pump power) was 69.05%, with the laser beam quality factor M2 of 1.2. No obvious power decaying of the laser output was observed for about 10 h. RD and bleaching effects of the Yb3+-doped LMA PCF core glass have been thoroughly investigated using the absorption, radiation-induced attenuation (RIA), continuous wave electron paramagnetic resonance (CW-EPR), emission, Raman, and Fourier transform infrared (FTIR) spectra.

Five-Ce:Nd:YAG-rod solar laser approach with TEM00-mode collection efficiency of 51.7 W/m2

One of the major goals of solar-pumped lasers is to improve TEM00-mode collection and conversion efficiencies. Several studies have explored multi-rod designs with the aim of enhancing laser output and thermal management by distributing the absorbed solar energy across multiple rods. In this work, we introduced a concept comprising four Fresnel lenses with a total collection area of 3.14m2 and four aspherical lenses, which concentrated the sunlight into a water-flooded cylindrical cavity housing five side-pumped Ce:Nd:YAG rods. A beam-merging scheme was also proposed to generate a single output beam. Simulations performed with Zemax and LASCAD demonstrated that this configuration could produce a total TEM00-mode laser output of 162.3 W. The corresponding collection efficiency reached 51.7W/m2, with a solar-to-laser power conversion efficiency of 5.44%, representing improvements of 3.13 and 2.64 times, respectively, compared to the record experimental results from a system using a single Ce:Nd:YAG crystal and a Fresnel lens. Moreover, even when compared to a more complex seven-rod configuration, both efficiencies exhibited a 1.50 times increase.

High-contrast front end based on Yb: YAG solid-state laser for PW-level Ti: sapphire laser.

In this paper, we demonstrate a high-contrast front-end laser system based on Yb: YAG solid-state laser for Ti: sapphire terminal amplification. An ultrafast Yb: YAG solid-state laser is used to generate a broad-spectrum seed through white light generation (WLG), and then the signal light near 1600 nm is amplified by three-level colinear optical parametric chirped pulse amplification (OPCPA). Finally, a fs second harmonic generation (SHG) is used to obtain a laser output with a central wavelength of 795 nm, a pulse width of 40.2 fs, a contrast baseline of nearly 10-12 within 1 ns, and almost no ps pedestal. We used this laser system as a seed to amplify it to about the theoretical estimated 30 TW level, showing good dispersion properties and contrast preservation capabilities.

High-Energy Burst-Mode 3.5 μm MIR KTA-OPO

In this paper, a high energy 3.5 μm mid-infrared (MIR) burst-mode KTA optical parametric oscillator (OPO) was demonstrated. Utilizing a quasi-continuous wave (QCW) laser diode (LD) side-pump module and electro-optic (EO) Q-switching technique, a high beam quality 1064 nm burst-mode laser was achieved as the fundamental source, generating 30 mJ high-energy pulses at burst repetition rates of 100 Hz and 200 Hz with sub-burst repetition rates of 20 kHz, 40 kHz, and 50 kHz. The KTA-OPO produced a 3.5 μm MIR burst-mode laser output with 4 to 11 sub-pulses per pulse envelope. The output energies were 2.9 mJ, 2.81 mJ, and 2.79 mJ at 100 Hz, as well as 2.8 mJ, 2.75 mJ, and 2.72 mJ at 200 Hz, with corresponding conversion efficiencies of 9.6%, 9.3%, and 9.3% at 100 Hz, as well as 9.3%, 9.2%, and 9.1% at 200 Hz, respectively. Our results pave a new way for generating burst-mode MIR lasers.

Generation of 16 Micrometer IR Laser by theOptical Pumping of CF4 Gas Molecules

We report here the observation of 16 µm superradiance laser action generated from optical pumping of CF4 gas molecules (which is cooled to 140 Kº by a boil-off liquid-N2) by a TEA-CO2 laser 9R12 line. Output laser pulses of 7 mJ and 200 ns have been obtained.

Impact of chaotic semiconductor laser output power on the time-delay-signature of chaos and random bit generation

Impact of chaotic semiconductor laser output power on the time-delay-signature of chaos and random bit generation

Enhanced high brightness DBR tapered diode laser based on polarization match.

Tapered diode lasers, composed of an index-guided ridge waveguide and a gain-guided tapered amplifier, are affected by polarization mismatch between the ridge and tapered sections. Beam quality deterioration is caused by TM high-order modes generated in the ridge section. Under high current injection, these TM modes are further amplified in the tapered section due to polarization mismatch, leading to a decrease in the laser output brightness. In this paper, a combination of deep etching in the ridge section and compressive stress in the tapered section is employed to obtain a fundamental mode seed source with a high TE degree of polarization (DOP), simultaneously improving the polarization match between the ridge and tapered sections. The fabricated tapered diode laser achieves a beam quality factor of M2(1/e2) = 1.2 at an output power of 11.57 W. The peak electro-optical efficiency is 59.8%, and the maximum output brightness reaches 936 MW·cm-2·sr-1.

Breathers in Mode-Locked Lasers Based on Saturable Absorbers

Breathing pulses, as a unique nonlinear pulse phenomenon, play a key role in laser performance optimization, nonlinear optical processes, and complex signal transmission. Unlike stable solitons, the energy of breathing pulses fluctuates periodically over time, exhibiting periodic changes in both pulse frequency and amplitude. Through appropriate nonlinear effects, lasers can generate stable breathing pulses, achieving a mode-locked state that demonstrates a periodic "breathing" pattern. Based on this, a fiber laser incorporating a saturable absorber as the mode-locking element was designed and built, and stable breathing states were successfully observed at lower pump power levels. High-speed detection techniques and time-stretched dispersive Fourier transform (TS-DFT) technology were used to time-amplify and spectrally analyze the rapid pulses, while monitoring the evolution of the breathing pulse in both time and frequency domains. Experimental results indicate that changes in pump power significantly affect the periodic modulation induced by additional oscillations, thereby controlling the breathing ratio and ultimately leading to the formation of a stable soliton. When the pump power is between 470 <i>mW</i> and 480 <i>mW</i>, the formation of the breathing pulse was first observed, with a breathing ratio of up to 4.5. As the pump power increases, the breathing effect gradually diminishes, and at 510 <i>mW</i>, it completely disappears, with the breathing ratio dropping to 1.<br>These results confirm the critical role of pump power in controlling the breathing pulse state and its transition, demonstrating the potential for controlling pump power in ultrafast laser technology and nonlinear optics. The breathing pulse phenomenon, as a periodic pulse behavior, reflects the complex dynamical characteristics between nonlinear optical effects and cavity parameters. When combined with the natural synchronization system formed between the breathing frequency and the cavity frequency (determined by the cavity length), the periodic change of the breathing pulse becomes a crucial factor for controlling laser output. By adjusting parameters such as the laser’s nonlinearity and dissipation, the characteristics of the breathing pulse and breathing ratio can be precisely controlled, thus achieving precise control of the laser output. The periodic oscillatory characteristics of the breathing pulse inside the laser cavity lead to the non-uniform distribution of pulses, a feature that demonstrates enormous potential in pulse shaping, ultrashort pulse generation, and precise frequency comb control. Additionally, the presence of the breathing pulse may impact the stability and energy conversion efficiency of the laser, offering new perspectives for laser design and optimization.

Ultrafast laser frequency tuning based on equivalent optical phase sampling and accumulation

Ultrafast laser frequency tuning is a crucial function in numerous applications, including light detection and ranging (LiDAR), optical coherence tomography (OCT), and spectroscopy. In general, laser frequency tuning is realized via the motion of mechanical structures, frequency-swept optical filters, or the Pockels effect in the laser cavity. Nevertheless, the maximum frequency tuning rate and sweep rate are smaller than 107 THz/s and 1 GHz, respectively, due to the inherent speed limitation of the existing tuning mechanisms. Here, we propose and demonstrate a brand-new concept for ultrafast laser frequency tuning, which is realized based on equivalent optical phase sampling and accumulation in the laser cavity. By inserting an electro-optic phase modulator (PM) into the laser cavity and properly setting the period of the driving signal applied to the PM to make its integer multiple slightly deviate from the round trip time of the laser cavity, a linear mapping from the voltage of the driving signal to the output laser frequency is realized via equivalent optical phase sampling and accumulation. This remarkable feature provides a rapid way to manipulate the laser frequency, breaking the frequency tuning speed limitation of the existing approaches. In the experiment, a record-breaking frequency tuning rate of 1.522 × 109 THz/s and a sweep rate of 2223.97 MHz are simultaneously realized. Moreover, the center wavelength and the frequency tuning range can be easily reconfigured. This work paves the way for ultrafast laser frequency tuning in a customized wavelength range.

A Study on the Chemical Oxygen Iodine Lasers

Abstract: An example of a near-infrared chemical laser is a chemical oxygen iodine laser (COIL). The beam is invisible to the human eye since it is infrared. In continuous mode, its output power can scale up to megawatts. Its output wavelength is 1315 nm, which equals atomic iodine's transition wavelength.[23] The Air Force Research Laboratory created the chemical oxygen iodine laser (COIL), an infrared chemical laser, in 1977 mainly for military use. The laser's output power can be up to megawatts when operating in continuous mode. [22]

Analysis of Low-Threshold 1D Perovskite Photonic Crystal Laser

By using the bandgap effect and light localization effect, photonic crystal lasers can decrease the optical mode volume and lower the laser threshold, so satisfying the requirements for device shrinking and photonic integration. Given their wide range of potential applications in fields including light-emitting diodes and sensors, they are attracting considerable interest. The laser threshold is the minimum energy density required to cause laser oscillation and is a crucial specification for the practical application of laser devices. Perovskite materials, equipped with their exceptional optical gain characteristics, are well-suited for the development of low-threshold lasers. By combining them with photonic crystal lasers, it is possible to realize low-threshold or even threshold-free pumped lasers. This paper categorizes photonic crystal lasers according to their photonic crystal structures and examines the advancements in research on perovskite photonic crystal lasers in attaining low minimum thresholds. This work investigates the prospective capabilities of perovskite photonic crystal lasers, with the objective of achieving laser output that is low-threshold or near-zero-threshold, high-power, and of high quality.

Exploring Organic-Based Saturable Absorption Focusing on Spider Silk in Q-Switched Pulse Fiber Laser Applications: A Mini Review

The fiber laser combines the fiber gain medium's function as a fiber amplifier, transforming it into laser output through integration within a cavity configuration. Meanwhile, a pulsed fiber laser is capable of generating short bursts of laser emission characterized by high peak power levels. This concept is known as Q-switching. A saturable absorber material is essential for passive Q-switching, as it is integrated into the laser cavity to produce an instantaneously Q-switched pulse fiber laser. While these materials have been effective in generating pulsed lasers, they often come with unresolved issues, such as long-term exposure to two-dimensional materials can pose health risks. To address this gap, researchers have shifted their interest toward natural or organic materials in the quest for new saturable absorbers. This mini-review provides a comprehensive overview of the saturable absorber mechanism, including essential theoretical equations and key measurement parameters. The next section continues by exploring the fundamentals and early development of saturable absorbers, followed by an in-depth explanation of the Q-switched pulse generation process using erbium-doped fiber as the gain medium and saturable absorber. Critical parameters influencing the performance of Q-switched pulse fiber lasers are discussed, with special attention given to recent advancements in organic-based saturable absorbers for Q-switching. The potential of spider silk as an innovative saturable absorber in Q-switched pulse fiber laser applications is highlighted. Finally, the review delves into the wide-ranging applications of these lasers, including tunable and switchable dual-wavelength fiber lasers with sensor for temperature measurement and to detect adulteration in pure kelulut honey and sucrose solution.

All-fiber E + S band continuously tunable bismuth-doped germanosilicate fiber laser

In this Letter, we present an all-fiber bismuth (Bi)-doped germanosilicate fiber laser that is continuously tunable within the range of 1425–1475 nm, enabled by a tunable optical filter. A maximum output power of 86.4 mW was achieved at 1450 nm with a slope efficiency of 13.7%. It is, to the best of our knowledge, the first demonstration of an all-fiber tunable continuous-wave (CW) bismuth-doped fiber laser (BDFL) operating in the E + S band. Moreover, a bismuth-doped fiber amplifier (BDFA) was constructed to further scale the laser output power to 159.2 mW with a 21% slope efficiency. Across the 1425–1475 nm range, we achieved >117 mW output power with >50 dB in-band optical signal-to-noise ratio (OSNR).

Study on the Effect of Laser Power on the Microstructure and Properties of Cladding Stellite 12 Coatings on H13 Steel.

To address the issue of cracking in aluminum extrusion dies during operation, this study employs laser cladding technology to modify the surface of these dies. This modification aims to enhance their hardness and friction resistance. Laser cladding technology was utilized to coat the surface of H13 steel with Stellite 12, a cobalt-based alloy, at varying laser power levels. The surface formation quality, microstructural organization, phase composition, microhardness, and wear resistance of the coatings were investigated using optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction (XRD), microhardness testing, and confocal microscopy. The results indicated that as the laser power increased, the surface formation quality of the coating gradually improved, while the dilution rate of the coating increased. Changes in the phase composition and microstructure were not significant, and both microhardness and wear resistance initially increased before decreasing. Optimal process parameters for achieving good surface formation quality, high microhardness, and strong wear resistance were found to be a laser output power of 2200 W, scanning speed of 10 mm/s, feeding rate of 1.2 r/min, and overlap rate of 40%. The results indicate that the coating applied to the surface of H13 steel using Stellite 12 enhances the performance of aluminum extrusion dies.