Quality M2 Research Articles

Compact Partially End-Pumped Innoslab Laser Based on Micro-Cylindrical Lens Array Homogenizer

We demonstrate a compact, partially end-pumping Innoslab laser based on a micro-cylindrical lens array homogenizer. A dimension of 12 × 0.4 mm2 flat-top pumping line with a Gaussian intensity distribution across the line was simulated by the ray tracing technique. The rate equations considering the asymmetric transverse spatial distributions are theoretically developed. The simulation results are in good agreement with the experimental results. Preliminary data shows that for a pump power of 260 W, a maximum pulse energy of 15.7 mJ was obtained with a pulse width of 8.5 ns at a repetition frequency of 1 kHz. The beam quality M2 factors in the unstable and stable directions were 1.732 and 1.485, respectively. The technology has been successfully applied to temperature and humidity profiling lidar and ozone lidar and has been productized, yielding direct economic value.

Monolithic linear array fiber end cap for spectral beam combination

In this study, a fusion splicing system that facilitates the splicing of a monolithic linear array fiber end cap is constructed. The fusion splicing thermal field of the end cap irradiated by a CO2 laser is theoretically simulated using the finite element method. The experimental fusion splicing temperature agrees well with the simulation results. The splicing strength, misalignment, and high-power withstanding capacity of the fusion-spliced monolithic linear 3-fiber end cap are investigated. The use of the fabricated device in a dual-grating spectral beam combination (SBC) is also demonstrated with three-channel laser beams, achieving a combined beam with near-diffraction-limited beam quality M2=1.101. It shows that the development of the monolithic linear array fiber end cap is meaningful for achieving a compact high-brightness SBC system.

Study on narrow linewidth 2.1 μm self-optical parametric oscillator based on Nd:MgO:PPLN

We report a 2.1 µm miniaturized narrow linewidth self-optical parametric oscillator (SOPO) based on Nd:MgO:PPLN crystal. We attained 2.1 µm narrow linewidth laser output by incorporating an Fabry-Perot (F-P) etalon into the SOPO. By controlling the crystal temperature uniformly, a stable 2.1 µm degenerate light output is obtained at 71 °C. Finally, when inserting the F-P etalon with a thickness of 2.5 mm, a maximum average output power of 0.65 W is obtained, corresponding pulse repetition rate is 60 kHz, the pulse width is 7.77 ns, the degenerate light beam quality M2 < 2. And the linewidth of 2168 nm laser is narrowed from 67.53 nm to 2.23 nm. It is proved by experiments that adding F-P etalon to the SOPO can narrow the linewidth of the 2.1 μm laser and optimize the beam quality. These findings provide technical support for the realization and application of narrow linewidth 2.1 µm laser, which is great significance for the further development of related fields.

Time–Frequency and Spectrum Analyses of All-Solid-State Self-Mode-Locked Burst Pulse Lasers

The theoretical and experimental characteristics of all-solid-state self-mode-locked burst pulse lasers are investigated in this study. The time–frequency and spectrum analyses of the lasers incorporating Fabry–Pérot (F-P) structures are presented, along with the development of the corresponding theoretical model. Self-mode-locked burst pulse lasers are experimentally constructed to reduce intracavity losses using the front and rear end surfaces of the gain media to form F-P structures. When the laser cavity length is 600 mm and the gain media lengths are 5, 6, and 10 mm, each burst pulse produced contains 56, 47, and 28 subpulses, respectively, with the same burst pulse width of 2 ns. The burst pulse train with beam quality M2 = 1.37 and an average output power of 0.23 W is obtained when the gain medium length is 5 mm and the pump power is 4.5 W. The corresponding burst pulse repetition frequency is 0.25 GHz and the subpulse repetition frequency is 13.66 GHz. The time–frequency spectral analyses of the laser signals provide a good representation of laser spectral information that even the currently available highest-resolution spectrometers cannot resolve.

Assessing the effect of sample storage time on viral detection using a rapid and cost-effective CTAB-based extraction method

BackgroundCassava leaf samples degrade quickly during storage and transportation from distant areas. Proper sampling and efficient, low-cost storage methods are critical for obtaining sufficient quality DNA and RNA for plant virus epidemiology and improving disease control understanding. This is useful when samples are collected from remote areas far from a laboratory or in developing countries where money and materials for virus diagnostics are scarce.ResultsThe effect of sample storage duration on nucleic acid (N.A.) quality on virus detection was investigated in this study. A simple, rapid, and cost-effective CTAB-based approach (M3) for single N.A. extraction was optimized and tested alongside two existing CTAB-based methods (M1 and M2) for N.A. extraction from fresh and herbarium cassava leaves stored for; 1, 8, 26, and 56 months. The amount and quality of DNA and RNA were determined using Nanodrop 2000 c U.V.–vis Spectrophotometer and agarose gel electrophoreses. The sample degradation rate was estimated using a simple mathematical model in Matlab computational software. The results show no significant difference in mean DNA concentration between M1 and M2 but a significant difference between M3 and the other two methods at p < 0.005. The mean DNA concentration extracted using M3 was higher for 1 and 8 months of leave storage. M3 and M2 produced high concentrations at 26 and 56 months of leave storage. Using a developed scale for quality score, M3 and M2 produced high-quality DNA from fresh samples. All methods produced poor-quality DNA and RNA at 8 and 26 months of leave storage and no visual bands at the age of 56 months. Statistically, there was a significant difference in the mean DNA quality between M1 and M2, but there was no significant difference between M3 and the other two methods at p < 0.005. However, Cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) were readily detected by RT-PCR from RNA isolated using M3. The quality of DNA declined per storage time at 0.0493 and 0.0521/month, while RNA was 0.0678 and 0.0744/month. Compared to the existing two methods, modified CTAB extracted enough high-quality N.A. in one-third the time of the existing two methods.ConclusionOur method provides cost-effective, quick, and simple processing of fresh and dry samples, which will quicken and guide the decision on when and what type of sample to process for plant disease management and surveillance actions.

High-power polarization-maintaining LP11-mode fiber laser based on long-period fiber grating for precise welding.

An LP11-mode output all-fiber laser was presented, utilizing long-period fiber gratings (LPFGs) and polarization-maintaining optical fiber (PMF). The LPFG was designed and fabricated, achieving a 90.56% efficiency in LP01 to LP11 mode conversion. Furthermore, the transmission stability of LP11-mode in the PMF was also explored, with the spatial mode overlap ratio exceeding 0.95. Ultimately, the high-power polarization-maintaining (PM) fiber laser, capable of the LP11 mode output, was constructed, with the output power of 600 W and the beam quality M2 of 2.84. During the process of welding a thick Al-plate, the LP11 fiber laser exhibits a notable 1.88 times greater depth of fusion compared to the commercial single-mode fiber laser, when operating at the laser welding head speed of 100 mm/s. For applications demanding non-circular symmetric high-order modes, this research holds substantial potential for widespread adoption within the field of industrial processing.

High brightness edge-emitting laser diode with wavelength self-organization in ultra-broad emitting area.

We have proposed and experimentally demonstrated an efficient method for generating high power and brightness based on an ultra-broad area laser diode (UBALD). We have developed a single-emitter UBALD capable of self-organization multi-wavelength emissions for two stripe widths of 2 and 5 mm, respectively. The 2 mm UBALD delivers an output power of 55 W with a beam quality M2 of 1.3 × 25.3 and a brightness of 179 MW/(cm2·sr). The 5 mm UBALD produces an output power of 121 W with a beam quality M2 of 2.1 × 32.7 and a brightness of 192 MW/(cm2·sr). To the best of our knowledge, these results represent the highest output power and highest brightness ever achieved from a single edge-emitting LD emitter to date.

Diode-pumped high-peak-power nanosecond Nd,Y: SrF2 regenerative laser amplifier

We demonstrate a regenerative laser amplifier based on laser-diode-pumped Nd, Y:SrF2 crystals with an output of approximately 9.78 mJ/10 Hz. A specially designed birefringent filter was inserted into the cavity to compensate the gain narrowing and amplify the seed pulse with a center wavelength of 1053.3 nm. To optimize the design of the resonator, the thermal wavefront of the laser gain module was simulated and experimentally measured. When a laser pulse with a duration of 9 ns and energy of 1 nJ was injected into the regenerative amplifier, the output energy was 9.78 mJ with peak power of 1.1 MW. The energy stability was 0.72 % RMS. The horizontal and vertical beam quality M2 was 1.18 and 1.23 respectively. The results show the potential of the developed amplifier for application in high-power laser facilities.

Brightness enhancement on random-distributed-feedback Raman fiber lasers pumped by multimode diodes

Abstract The power scaling on short wavelength (SW) fiber lasers operating around 1 μm are in significant demand for applications in energy, environment and industry. The challenge for performance scalability of high-power SW lasers based on rare-earth-doped fiber primarily lies in the physical limitations, including reabsorption, amplified spontaneous emission and parasitic laser oscillation. Here, we demonstrate an all-fiberized, purely passive SW (1018 nm) random-distributed-feedback Raman fiber laser (RRFL) to validate the capability of achieving high-power output at SWs based on multimode laser diodes (LDs) direct pumping. Directly pumped by multimode LDs, the high-brightness RRFL delivers over 656 W, with an electro-optical efficiency of 20% relative to the power. The slope efficiency is 94%. The beam quality M2 factor is 2.9 (which is ~20 times that of the pump) at the maximum output signal power, achieving the highest brightness enhancement of 14.9 in RRFLs. To the best of our knowledge, this achievement also represents the highest power record of RRFLs utilizing multimode diodes for direct pumping. This work may not only provide a new insight into the realization of high-power, high-brightness RRFLs but also is a promising contender in the power scaling of SWs below 1 μm.

Tracing the origins of mode coupling for beam quality optimization in high-power fiber laser delivery systems

Abstract Suppressing mode degradation is the key issue for high-power laser delivery; however, diagnosing mode degradation in its entirety, ranging from the contents and origins to locations, has always been a major obstacle. Here, a versatile approach for tracing the origins of mode coupling is demonstrated through addressing the differential intermodal dispersions of fiber modes. Full recognition for modal contents and the origins of mode degradation are experimentally completed in a two-mode fiber laser delivery system, which assists a significant improvement of beam quality M2 from 1.35 to 1.15 at the highest power of over 300 W. This method yields a quantitative characterization for manipulating the individual mode of dual-mode coupling origins or their combinations. This work points toward a promising strategy for the online tracing of mode coupling in cascade fiber links, thus enabling further pursuit of seeking extreme beam quality in high-power fiber laser systems.

All-solid-state CW Pr3+:YLF green laser at 522 nm end-pumped by a high-power fiber-coupled 444 nm blue LD module

Continuous wave (CW) green lasers have a lot of important applications in many fields, including holography, interferometry, atom cooling and trapping, and quantum optics, and they are usually achieved by frequency-doubling 1 µm lasers based on the Nd3+ gain media. In this paper, we present an all-solid-state CW green laser with an output wavelength of 522 nm, which was directly attained by employing a Pr3+:YLF crystal pumped with a high-power fiber-coupled blue laser diode (LD) module as the gain medium. Due to the negative thermal lens effect of the Pr3+:YLF crystal, the designed laser resonator had to be lengthened with the increase in the incident pump power. As a result, when a 0.5% doped Pr3+:YLF crystal was employed as the gain medium and the incident pump power was 12 W, the length of the resonator was optimized to 311.3 mm and the maximum output power of 522 nm green laser was up to 886 mW. The obtained conversion efficiency and beam quality M2 were 11.25% and 1.15, respectively. The long-term power stability within 4.5 h was better than ±1.5% at an output power of 700 mW. The obtained watt-level green laser can also be used to generate high power CW deep UV laser for laser processing of silicon and organic materials, inspection, etc.

Compact Q-switched Tm:YLF laser with high slope efficiency, high power stability and high beam quality

This paper presents a high-efficiency and actively Q-switched Tm:YLF laser with a compact design by arranging the optical elements closest to each other in a linear cavity. With a flat output coupler (OC), slope efficiency of 74.7% and output power of 12.41 W were achieved in continuous-wave operation. Using a volume Bragg grating (VBG) as the OC and wavelength selector, the output power and slope efficiency of the 1.908 μm laser were 10.65 W and 67.3%, respectively. The corresponding beam quality M2 was about 1.5 at the maximum power. The Tm:YLF laser with VBG revealed high stability with a power fluctuation of 0.45% and central wavelength variation of 0.23 nm for one-hour continuous testing. In pulsed operation at 10 kHz, average power of 10.07 W and slope efficiency of 66.0% were obtained. This actively Q-switched Tm:YLF laser of 10-W level will be an ideal pump source for compact and high-efficiency mid-infrared optical parametrical oscillators for practical applications.

Mitigation of TMI in an 8 kW tandem pumped fiber amplifier enabled by inter-mode gain competition mechanism through bending control.

In this work, the impact of fiber bending and mode content on transverse mode instability (TMI) is investigated. Based on a modified stimulated thermal Rayleigh scattering (STRS) model considering the gain competition between transverse modes, we theoretically detailed the TMI threshold under various mode content and bending conditions in few-mode fibers. Our theoretical calculations demonstrate that larger bending diameters increase the high order mode (HOM) components in the amplifier, which in turn reduces the frequency-shifted Stokes LP11o mode due to the inter-mode gain competition mechanism, thus improving the TMI threshold of few-mode amplifiers. The experimental results agree with the simulation. Finally, by optimizing the bending, an 8.38 kW output tandem pumped fiber amplifier is obtained with a beam quality M2 of 1.8. Both TMI and stimulated Raman scattering (SRS) are well suppressed at the maximum power. This work provides a comprehensive analysis of the TMI in few-mode amplifiers and offers a practical method to realize high-power high-brightness fiber lasers.

Nanosecond pulsed narrow-linewidth all-fiber source for ZGP-OPO pumping

We demonstrate a pulsed three-stage master oscillator power amplifier (MOPA) at a wavelength of 2047 nm and its application for mid-IR generation via pumping a ZnGeP2 (ZGP) optical parametric oscillator (OPO). A maximum MOPA output power of 19.8 W is reached while achieving a diffraction limited beam quality M2 &lt;1.1. By applying the MOPA setup to pump a ZGP crystal in a linear OPO cavity, a combined signal and idler mid-IR output power of 8.1 W is reached. For the highest mid-IR output power, a mid-IR conversion efficiency of 44 % and beam quality factors M2 of 2.2 and 2.0 are determined for signal and idler, respectively.

Dual-wavelength laser source by spectral beam combining of two Nd:YAG pulse lasers.

We present a dual-wavelength laser source obtained by spectral beam combining of two solid-state Nd:YAG pulsed lasers. The central wavelengths were locked at 1061.5 and 1064.6nm. The output energy was the sum of the energy of the individually locked Nd:YAG lasers. The beam quality M 2 of the combined beam is 2.8×2.2, which is nearly the same as that of a single Nd:YAG laser beam. This work should be helpful to provide an effective dual-wavelength laser source for applications.

Sub-nanosecond, 41 mJ pulse energy, passively Q-switched Nd:YLF laser

A sub-nanosecond, diode-stack side-pumped, passively Q-switched Nd3+:YLF4/Cr4+:YAG Laser is reported in a compact cavity design, generating one pulse of 41 mJ with a pulse width of 894 ps, achieving a peak output power of 46 MW and beam quality M2 of 5.4 × 5.9 (HxV). The number of pulses in the pulse train could be adjusted from one pulse to ten pulses of 111 mJ total output energy and 23.7 % optical efficiency by adjusting the focus distance while maintaining sub-nanosecond pulse duration. This resonator can also be used for high-power simultaneous Q-switched laser emission at 1047 nm and 1053 nm.

A 115 ps, 100 Hz high-beam-quality laser based on transient stimulated Brillouin scattering pulse compression

Abstract This work demonstrates the generation of short pulse duration and high-beam-quality laser pulses using transient stimulated Brillouin scattering at a high repetition rate. Thermal effects and optical breakdown are identified as the main factors that restrict energy reflectivity and beam quality under high repetition rates and transient situations. Through experimental analysis, the interaction length and focal point size are determined to be the key parameters in reducing the thermal effect by reducing the absorption of the laser pulse by the medium. The obtained results show that pulses with a duration of 175 ps and beam quality M2 of around 1.2 can be achieved with a maximum energy reflectivity of over 40% under an interaction length of 50 mm. Furthermore, at an interaction length of 90 mm, a pulse output with a minimum duration of 115 ps (0.5τQ) is achieved.

High efficiency and high beam quality Er:YSGG Mid-infrared continuous-wave laser

We demonstrated an LD end-pumped Er:YSGG mid-infrared (MIR) continuous-wave (CW) laser based on optimized LD pump wavelength with less absorption coefficient and thermal problems. A composite crystal YSGG/Er:YSGG/YSGG with a size of 3 × 3 × 14 (2 + 10 + 2) mm3 was employed, and its central part had an erbium ion doping concentration of 38 %. The maximum output power of 2.8 μm MIR laser is 2.01 W, corresponding to a slope efficiency of 28.89 %, at which the beam quality M2 of the laser is 1.19. Compared with other Er3+-doped laser, we achieved a CW MIR laser with higher efficiency and better beam quality. The results suggest that optimizing the wavelength of the pump source and adopting the crystal bonding technology could effectively improve the performance of the LD end-pumped Er:YSGG CW MIR laser.

Unmanned airborne miniaturized pulsed CO2 laser with wavelength automatic tuning

This paper presents a miniaturized mechanically Q-switched pulsed CO2 laser with wavelength automatic tuning, which could be used in unmanned airborne lidar system. A three-mirror cavity structure with real focus in the cavity is designed to provide a stable resonator, which has short beam transit time for mechanically Q-switched laser. The matching relationship between the beam in the resonant cavity and the aperture of the optical chopper is experimentally studied, the CO2 laser pulse output with good waveform is obtained, and the wavelength automatic tuning is realized. The CO2 laser produces a maximum output peak power of 3.7 kW at 10.59 μm for pulse width of 350 ns, corresponding beam quality M2 of 1.75, and the laser weight is about 18 kg.

Efficient Tm:LuYAG laser resonantly pumped by an Er:LuYAG laser

We demonstrate an efficient continuous-wave (CW) and Q-switched Tm:LuYAG laser that was resonantly pumped by an Er:LuYAG laser. The maximum CW output power was 3.12 W, and the corresponding slope efficiency relative to the incident pump power was 51.4%. In the Q-switched mode, a stable laser pulse was achieved from 1 to 10 kHz repetition frequency under the maximum incident pump power of 7 W. The narrowest pulse width of 94 ns with a pulse energy of 2.12 mJ was obtained at 1 kHz, resulting in the highest single pulse peak power of 22.5 kW. The Tm:LuYAG laser was centered at 2018.37 nm with a high-beam quality M2 < 1.2.