This PDF file contains the front matter associated with SPIE Proceedings Volume 12310, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

High mode purity of high-power fiber lasers is strongly required in 3-dimensional printing, high brightness beam combing, and high accuracy material processing. Mode decomposition (MD) is an effective technique for diagnosing the mode composition of a high-power fiber laser. In particular, dynamic mode evolution could be commonly generated during power scaling process due to thermal and nonlinear effects. Consequently, the fast and accurate mode decomposition (MD) method is strongly required. The non-iterative fast mode decomposition based on matrix operation method is theoretically a promising technique to achieve ultra-fast MD with high accuracy. However, this technique of realizing MD is mainly limited by the noise of the light-spot image in a practical system. In this report, the effect of the image noise on the noniterative fast mode decomposition technique is carefully investigated. Simulation results show that the decomposition accuracy decreases as the intensity of noise increases. Nevertheless, the effect of image noise on the non-iterative fast mode decomposition method depends not only on the noise intensity but also on the coefficient matrix condition number of the matrix equations. Furthermore, the higher the condition number of coefficient matrix of linear equations is, the more influence of image noise on the non-iterative fast MD accuracy. The results presented could give instructive reference for further optimizing the non-iterative fast mode decomposition technique used in practical high-power fiber lasers.

To achieve multi-petawatt pulses, the generation of high-temporal-contrast few-cycle seed pulses with the central wavelength of 910 nm is the first step. In this research, high-performance seed pulses with a spectrum ranging from 800 nm to 1050 nm and pulse energy of 86 μJ are generated based on the filtered multi-plate spectral broadening and spectral filtering from a Yb-based femtosecond laser system. With self-phase modulation (SPM) induced spectral broadening, the input with relatively narrow spectrum bandwidth is broadened widely, which enables the final output pulse be compressed from full width at half maximum (FWHM) of 190 fs to 11.2 fs and a compression ratio of about 18 after dispersion compensation. The experiments show that the temporal contrast of the final output pulse is improved by at least four orders of magnitude through spectral filtering and new spectral components generated by third-order nonlinear processes such as SPM and self-focusing. Furthermore, taking advantage of single beam and self-focusing process, the final output has high energy stability and spectrum stability. Based on the merits above, together with its simplicity and robustness, this method proposed is expected to be used for the seed pulse generation of 10s-100s petawatt (PW) level laser system in the future.

Generation of 265-fs millijoule pulses at 1940 nm from a solid-state regenerative amplifier has been demonstrated. The system consists of a thulium-doped fluoride (Tm:ZBLAN) fiber oscillator, a two stage Tm:ZBLAN fiber preamplifier, and a regenerative amplifier with a thermoelectrically cooled thulium-doped yttrium aluminium perovskite crystal. The newly developed light source is used for pumping an ultra broadband mid-infrared optical parametric amplifier based on a gallium selenide crystal. The 2.5–4 μm range of a multioctave supercontinuum, generated in a polarization-maintaining ZBALN fiber, is used as the MIR seed. The amplified signal in combination with the corresponding idler pulses spread from 2.5 to 10 μm in a collinear geometry.

This conference presentation was prepared for the Advanced Lasers, High-Power Lasers, and Applications XIII conference at PA22 SPIE/COS Photonics Asia, 2022

We demonstrate comparatively the laser performance of 970 nm laser diode (LD) side-pumped Er:YSGG crystals with a length of 85 mm and diameters of 2, 3, and 4 mm. The maximum average powers of 25.18, 25.74, and 20.41 W are achieved at 150 Hz and 200 μs, corresponding to the slope efficiencies of 30.01%, 31.47%, and 24.38%, respectively. The experimental results show that the Er:YSGG crystal rod with a diameter of 2 mm has no obvious advantage in laser output at low frequency and low pump power because the gain volume is small and the pump power cannot be fully absorbed, resulting in the gain saturation phenomenon. However, it exhibits the best laser output under high repetition rate and high pump power. The average power of 16.47 W obtained at 500 Hz is still not saturated. The beam quality factors M² in the x and y direction are determined to be 3.15/3.12, respectively, which is significantly better than those of the rods with diameters of 3 and 4 mm. All the results indicate that the crystal rod with a smaller diameter has better thermal management due to its larger specific surface area and better cooling ability, which is conducive to improving laser performance under the high repetition rate and high pump power operation.

A passively Q-switched dual-wavelength laser with pulsed LD coaxial end-pumped configuration was demonstrated. A theoretical model was built to simulate the dynamic process of the pulsed LD coaxial end-pumped dual-wavelength laser. Experimental verifications were carried out based on Nd:YAG/Nd:YAP crystals. When the reflectivity of the output mirror and the initial transmission of the saturable absorber were both 50%, the maximum output single-pulse energy of pulsed-pumped passively Q-switched dual-wavelength laser was 304 μJ, which was obviously enhanced compared with that in the CW pumping.

High power narrow-linewidth fiber lasers have been highly desired for various applications. In this paper, we presented new considerations of high power narrow-linewidth fiber amplifiers operating within 1030~1060 nm by using newgeometry active fiber, and the power-breakthrough operating at 1050 nm was achieved. We also reported our recent achievements on power scaling of high-power narrow-linewidth fiber lasers which operates within 1060~1080 nm based on system-optimized step-index and confined-doped active fibers, including linear-polarized and stochastic-polarized ones. Meanwhile, our new progress on special designed active fibers assisted high power fiber amplifiers with sub-GHz to within 1.5 GHz were demonstrated. Besides, the basic considerations of end-reflection on the SBS and SRS effects will be discussed, which provide a new insight for the suppression of SBS and SRS effects.

Based on the rate equation of passively Q-switching, the effects of pump rate on the pulse timing jitter was simulated. The evolution of pulse jitter versus initial transmittance of the saturated absorber and pump power were experimentally investigated using different Nd:YAG/Cr:YAG bonded crystals. By adopting reasonable parameters, it was proved that the pulse jitter of passively Q-switching could be controlled within hundreds of nanoseconds. If an actively Q-switched laser was used as the seed laser for a passively Q-switched microchip laser, the pulse jitter could be reduced down to ~5 ns, and the output characteristics of the passively Q-switched laser with seed injection were discussed.

We demonstrate single-longitudinal-mode and wavelength-tunable operation of Er:Y₂O₃ ceramic laser at ~1.6 μm using in-house fabricated low scattering loss ceramic sample and in-band pumped by an Er,Yb fiber laser at 1535 nm. Narrow linewidth and tunable laser operation has been realized using intracavity etalon of proper thickness for wavelength tuning and mode selection, yielding a wavelength tuning span of ~89 nm in the range of 1574.4 nm–1581.1 nm, 1599.4 nm-1601 nm, 1637 nm-1641.8 nm, and 1661.4 nm–1663 nm, respectively. Single-longitudinal-mode operation was confirmed using a scanning Fabry–Perot interferometer in the whole wavelength tuning range when output powers lower than ~35 mW.

With the help of multimode fibers (MMFs), spatiotemporal mode-locked (STML) lasers emerged recently, with promising applications and abundant high-dimensional nonlinear dynamics inside the cavities. Various STML MMF lasers have been experimentally demonstrated, with different cavity structure and different MMFs. Some theoretical models have been proposed for STML MMF lasers. However, these models are only applicable to the MMF lasers with specific cavity structure and limited parameter space. In this paper, a general theoretical model is presented, considering the linear and nonlinear gain, linear dispersion and nonlinear optical effects, spectral and spatial filtering effects, and the refractive index distribution of the MMF. Based on the theoretical modes, the influences of cavity parameters on the 3D soliton dynamics of the MMF cavities is demonstrated.

We propose and demonstrate a simple method to generate an all-fiber CVBs and LP₀₁ mode switchable laser using a few-mode fiber Bragg grating. A few-mode circulator is used to output the excited high-order modes. By adjusting the temperature to change the laser wavelength in the cavity, switching of the fundamental mode and the radial and azimuthally polarized laser is realized and their efficiencies are 10.76% and 5.55%, respectively. The purity of the radial and the azimuthally polarized beam is higher than 98%. The working wavelength of the radial and the azimuthally polarized beam is 1549.6nm. The 30 dB bandwidth is less than 0.15 nm, and the side mode suppression ratio is more than 73dB.

This conference presentation was prepared for the Advanced Lasers, High-Power Lasers, and Applications XIII conference at PA22 SPIE/COS Photonics Asia, 2022

Laser performance of Yb³⁺-doped silica fiber laser at 980 nm and 1064 nm was investigated theoretically and experimentally. Significantly degraded laser output power at 980 nm was analyzed with photodarkening characterization of the Yb³⁺-doped silica fiber when lasing at 980 nm and 1064 nm, which shows that the Yb³⁺-doped fiber laser power difference between simulation and experiment is proportional to the level of photodarkening related to population inversion.

The mode-locked lasers based on nonlinear polarization rotation (NPR) are applied in many fields such as optical communication, precision metrology and material processing due to simple structure, low cost and versatile states. In this paper, a compact Erbium-doped all-fiber mode-locked laser based on NPR is presented. The ring laser cavity consists of only a single in-line integrated device. The repetition of the laser is ~209MHz with 50 nm spectrum width and 236 fs pulse width. The laser can be utilized in the fields of precision measurement, optical sensing, optical communication, material processing and medical imaging.

This conference presentation was prepared for the Advanced Lasers, High-Power Lasers, and Applications XIII conference at PA22 SPIE/COS Photonics Asia, 2022

This conference presentation was prepared for the Advanced Lasers, High-Power Lasers, and Applications XIII conference at PA22 SPIE/COS Photonics Asia, 2022

We propose and experimentally demonstrate a stable and tunable PT-symmetric single-longitudinal-mode (SLM) fiber ring laser using a nonreciprocal Sagnac loop. To suppress multiple-longitudinal-mode oscillation, the Sagnac loop only including a 3-dB optical coupler (OC) and a polarization controller (PC) is incorporated into the fiber ring cavity, which induces nonreciprocal light transmission and coupling between the frequency-degenerate clockwise (CW) and counterclockwise (CCW) resonator modes. The two light paths traveling along the CW and CCW directions in the Sagnac loop are defined as the gain loop and loss loop, respectively. By adjusting the polarization states of the two light waves, when the gain and loss coefficients are larger than the coupling coefficient, the PT symmetry is broken, singlemode lasing is thus generated in the fiber laser cavity.

We report on gain- and Q-switched operation of Er:Y₂O₃ ceramic laser at 1640 nm using in-house fabricated lowscattering-loss, 0.25-at.% Er³⁺ -doped ceramic sample. Stable gain-switched operation in pulse repetition frequencies(PRFs) of 5-50 kHz has been demonstrated using an acousto-optic modulator switched 1535 nm fiber pump source, resulting in a peak power of 16 times higher than that for CW operation. Q-switched operation in 0.5-10 kHz repetition rate has been demonstrated with AO switcher, generating stable pulses of 94 ns duration and 0.5 mJ energy at 0.5 kHz for 5.7 W of absorbed pump power, corresponding to a peak power of 5.2 kW.

In this paper, a 1 kW fiber laser with phase-change cool storage technique is proposed and demonstrated. The phase change materials (PCMs) containing copper foam are filled into the heat sink of the fiber laser. The waste heat can be quickly diffused into the PCMs due to the high thermal conductivity and enormous surface area of copper foam. The fiber laser has a maximum output power of 1.2kW, an electro-optical efficiency of roughly 38%, a weight of roughly 17kg, and a dimension of 330×370×86 mm³ . The fiber laser can operate at maximum power for more than 5 minutes. The power-to-weight ratio of the fiber laser is around 70W/kg (not include power supply equipment).

We introduce the concept of frequency stepwise fiber laser and its potential application in gas spectroscopy with simple time-domain retrieval. Three different setups of the in-loop frequency shifter are demonstrated with different options of frequency step sizes. Spectroscopy in O₂ and CO₂ is carried out in gas cell to verify the spectral retrieval capability. The retrieved curves are in good agreement with the calculated results from HITRAN database. The output wavelength band of such a frequency stepwise fiber laser can be further extended with different in-loop gain fiber and/or nonlinear frequency conversion, providing promising solutions to practical spectroscopy of many important gases.

Efficient orthogonally polarized lasers (OPLs) with power balance is of great significance in many fields. A gain-selfbalanced coaxial-end-pumped orthogonally polarized laser is proposed in this presentation. Using the orthogonal Nd:YVO₄ crystal arrangement and a quarter wave plate, different waves were amplified by both crystals and the OPL could operate under the optimized condition. Compared with traditional methods, the beam quality and the coherence of the OPL were greatly improved and the coherence could also be actively switched by pump conditions. Theoretical explanations and discussions were given from the view of thermal effects and laser resonators. It is believed the gain-self-balanced coaxialend-pumped OPL has broad application prospects in precision measurement and other fields.

Combining the respective advantages of Nd:YAG and Nd:YVO4 crystals in achieving the 1.06-μm band laser, we proposed and demonstrated a highly efficient acousto-optically (AO) Q-switched dual-crystal hybrid gain laser. It not only had excellent power performance but also exhibited satisfactory polarization characteristics across a broad pulse repetition frequencies (PRFs) range. Under 42.00-W incident pump power, the maximum average output powers were 12.10 W and 19.64 W at the PRFs of 10 kHz and 200 kHz, respectively. The corresponding optical-to-optical efficiency rose from 28.81% to 46.76%. The results were significantly better than those of the conventional single-crystal laser in our control experiments. The laser polarization ratios at maximum average output power were ~7.6:1 and ~11:1 when the PRFs were 10 kHz and 200 kHz, respectively.

In recent years, layered transition metal sulfides (TMDCs) exhibit excellent nonlinear saturable absorption properties in laser modulations. Nevertheless, few of them are applied to the optimization of optical parametric oscillators (OPOs). In this work, we prepared a 12.5 nm-thickness platinum disulfide (PtS₂) saturable absorber (SA) by a combination of electron beam evaporation (EBE) and post-vulcanization method. The nonlinear transmittance is measured, which exhibits the SA characteristic of PtS₂ film. The acousto-optic (AO) Q-switch and the prepared PtS₂ SA are used to realize the operation of active and passive Q-switched OPO, and the mid-infrared idler pulse with nanosecond width is obtained. By measuring the experimental output results, the optimizations of PtS₂ SA to OPO’s operation are analyzed, including the stabilization of pulse train by 240%, the compression of idler-light pulse by 59.7%, the improvement of peak power by 198%. As a result, the improvement of nonlinear conversion is attained by 16.9%. The phenomenon may be due to the excellent saturable absorption effect of PtS₂ SA to the fundamental light. This paper shows the optimization effect of the prepared layered transition metal sulfide for laser intracavity modulation on the nonlinear frequency conversion process, especially for the improve of nonlinear conversion effect.

Based on the high photoluminescence quantum yield, broad absorption spectrum, and narrow symmetrical emission spectrum, perovskite quantum dots (QDs) have been adopted in pulsed laser generation as a saturable absorber, either organic or inorganic perovskites. In the paper, we improved the nonlinear absorption of CsPbBr₃ QDs by non-covalent doping of Au particles, and the nonlinear absorption properties of the prepared Au-doped CsPbBr₃ saturable absorber(SA) were characterized using the Z-scan system. A Q-switched laser output characteristics were obtained by building a Nd:YLF laser. We obtained a stable output average power of 815 mW and the minimum pulse width was 304ns. It shows that quantum dots can be modified to obtain better nonlinear coefficients by doping, showing potential application in the field of laser modulation.

Q-switched laser is one of the important techniques to achieve high-energy laser pulses and greatly promotes the development and application of the field of optical engineering. With the modulation of cavity loss by optical switch in the laser cavity, the energy output by the laser is compressed into a pulse with a very short duration. For passively Q-switched lasers, saturable absorbers (SAs) with nonlinear saturable absorption are commonly used as optical switches. In recent years, 2D materials are used widely as SAs, such as topological insulators, black phosphorous, transition metal dichalcogenides and transition metal oxides. As one of the TMDs, the antimonous sulfide (Sb₂S₃) with smaller band gap as well as excellent nonlinear optical properties is a promising SA material. In this paper, we demonstrate a passively Q-switched erbium-doped fiber laser based on Sb₂S₃ SA, which could generate stable short pulses. By utilizing the Sb₂S₃ SA fabricated with optical deposition method, an all-fiber cavity is built. In the experiment, a stable Q-switched pulse trains with a repetition frequency of 30 kHz, a central wavelength of 1558.4 nm and a pulse width of 6.4 μs are obtained at a 980 nm pump power of 35 mW. The signal-to-noise ratio of radio-frequency spectrum at the fundamental frequency is about 50 dB, indicating the high stability of the Q-switched pulse. To the best of our knowledge, this is the first demonstration of Q-switched fiber laser based on Sb₂S₃ material, which could contribute as a new potential SA material for pulsed fiber lasers.

We experimentally demonstrated a fiber laser with tunable linewidth based on self-injection locking (SIL) and the stimulated Brillouin scattering (SBS) effect. The linewidth-tuning operation is achieved by limiting injection power within the third regime of the feedback effect. SBS can realize single longitudinal mode (SLM) by the ultra-narrow gain range, and generate ultra-narrow laser linewidth because of the high Q value. Additionally, we use Brillouin erbium fiber laser (BEFL) to replace the ordinary Brillouin ring cavity to obtain better SLM property. The lasing with ultra-narrow linewidth is steadily emitted after eliminating the mod-hopping caused by SIL and confirming the stable occurrence of SBS. In addition, The Lorentzian linewidth of DFB (1.7 kHz) and SIL with different injection power are measured by the delayed self-heterodyne interferometry (50 km delay fiber). The Lorentzian linewidth of the BEFL (60 Hz) is accurately measured by the Voigt fitting.

In this paper, the rate equation of ytterbium ion concentration in the upper level and the transmission equations of seed signal, pump, and amplified spontaneous emission (ASE) are solved simultaneously by the explicit Runge Kutta method. Finally, a full spectral range of 1000~1130 nm seed power spectrum simulation is achieved. This paper focuses on the amplification of the seed signal at different peak wavelengths in different fiber lengths. The main works are as follows: The accuracy of calculation results by the iterative method has been improved. By constructing 3D data structure of seed signal, a parallel computing work on the propagation process of Gaussian-lineshape seed spectrum with a peak wavelength of 1020–1100 nm in ytterbium-doped fiber with a length of 1–30 m has been done, which makes the calculation time is significantly reduced. Finally, the reabsorption effect of seed signal at different peak wavelengths and the competition between the seed signal and ASE has been analyzed, and the optimal gain fiber length corresponding to the different peak wavelengths of the seed signal has also been discussed.

A diode pumped alkali laser (DPAL) provides a significant potential for construction of high-powered lasers. To realize the scaling of a DPAL, heat management should be optimized. In this paper, a new kind of gas-flowing DPAL was proposed, in which a small cross-flow fan with diameter of 125 mm was set in the center of a cylindrical vapor cell whose diameter and thickness is 160 mm and 55 mm, respectively. The gain medium of cesium and the buffer gas of ethane were filled in the vapor cell with the total pressure is about 1 atmosphere. A mathematical model was constructed to systematically study the influence of the rotate speed on the internal temperature distribution and the output features of the laser. And then, the experimental study of the laser system was then carried out, in which the output laser at 894.3 nm with power of 32 W was obtained. The results show that both the velocity distribution and temperature distribution are greatly influenced by the rotate speed of the cross-flow fan, and then the heat generated from the DPAL can be took away efficiently, which is very important to the output performance of the laser system. These results indicate that this new type of gas-flowing DPAL might be a good choice for power scaling of DPALs.

It is known that in the optical range quadratic nonlinear effects in solids appear at relatively low radiation intensities, while the radiation intensity required for a significant manifestation of cubic effects is much higher and can reach the damage threshold values. In this regard, quadratic effects dominate over cubic ones. In this work, it is analytically demonstrated that in the terahertz range the intensities required for the manifestation of cubic effects are much lower than in the optical range. In addition, their contribution to nonlinear effects can exceed the quadratic one by several orders of magnitude.

We study an opportunity to obtain low-threshold random Raman lasing in multimode diode-pumped graded-index (GRIN) fiber with enhanced backscattering in artificial fs-inscribed random structure. Proof-of-principle experiments have been performed with a 1-km multimode GRIN fiber of 100-µm core directly pumped by three fiber-combined high-power 940- nm LDs. The laser has half-open all-fiber cavity consisting of highly-reflective FBG which is UV-inscribed in GRIN fiber near the LD input and artificial random reflector near its output end. Different types of random structures were formed by the point-by-point femtosecond-pulse technique in the near-axis area of GRIN fiber core (different pitch, length and transverse profile). Comparison of their lasing properties in the multimode diode-pumped GRIN fiber has been performed. The lowest threshold of ~140 W and the highest output power of 6.2 W (at ~180 W pumping) with the beam quality M²~3.3 is achieved for 2D structure. It is shown that the quality is improved to M²~2.4 for 1D structure at the expense of slight reduction in output power (5.5 W).

The report considers prospects of development, on the basis of fibre lasers, of an ‘incoherent laser’ producing noise-like pulses. The possibility is demonstrated of a radically new radiation source occupying, in terms of output properties, an intermediate place between incandescent bulb and laser. Combination in such a laser of high output beam directivity, brightness and incoherent character of the radiation is quite important in many applications where speckle patterns of the light field are an undesirable effect.

We report on the investigation of a 7-core Yb-doped fiber laser based on femtosecond pulse written fiber Bragg gratings. The fabricated FBG arrays are used as a complex high-reflective mirrors, whereas output coupling is provided by ~4% Fresnel reflection from the normally cleaved end of the fiber. At cladding pumping by a 976-nm laser diode, the cores generate independently with linear total power growth up to 33 W at 50 W pump power. The individual generation spectra slowly broaden to ~0.15 nm whereas net spectrum at maximum power is ~0.2 nm broad thus demonstrating high-power narrowband generation in multicore active fiber.