Continuous-wave Output Research Articles

Exploring the criterion for the self-pulsing suppression of mid-IR intracavity OPO with self-Raman scattering.

The stimulated Raman scattering (SRS) from the Nd:YVO4 gain medium is originally employed to eliminate the self-pulsing effect from the intracavity optical parametric oscillator (OPO) for achieving a continuous-wave (CW) mid-infrared output. The SRS with a second-order pump-wave power depletion is applied as the damping for the coupling between OPO pump-wave relaxation oscillation and signal-wave depletion. The SRS threshold conditions for different cavity and diode-pumped mode size designs are theoretically and experimentally explored. By using different resonators, the CW mid-infrared output from 120 mW to 1.56 W at the diode pump power from 3 to 19.3 W can be successfully demonstrated.

Self-frequency-doubling Yb:GdCOB laser intracavity-pumped Pr:YAP laser

Abstract We present for the first time a Pr:YAlO3 (Pr:YAP) laser emitting at 547 nm intracavity-pumped by a self-frequency-doubling Yb3+:Ca4GdO (BO3)3 (Yb:GdCOB) blue laser at 488 nm. We carried out a model to design the system properly, and the laser performance was experimentally investigated. Intracavity sum-frequency mixing at 547 and 488 nm was then realized in a CsLiB6O10 (CLBO) nonlinear crystal to reach the ultraviolet laser at 258 nm. We obtained a continuous wave output power of 575 mW at 258 nm with a pump source, which is a diode-pumped quasi-three-level Sr1-x La x -y Nd y Mg x Al12-x O19 (Nd:ASL) laser emitting 11.2 W at 902 nm.

All-solid-state continuous-wave mode-locked Er:Lu2O3 laser at 3 µm

In this paper, we demonstrated stable continuous-wave passively mode-locked operation of an Er:Lu2O3 laser at 3 µm, utilizing a semiconductor saturable absorber mirror (SESAM). By operating the laser in a dry nitrogen environment and utilizing a thermoelectric cooler (TEC) temperature control device to mitigate the thermal effects of Er:Lu2O3 and enhance laser stability, we further compensated for group delay dispersion within the laser cavity through chirped mirrors, an shortest pulse duration of 12.0 ps at a average output power of 150 mW was achieved, which occurred at a center wavelength of 2844 nm, and a pulse repetition rate of 83.5 MHz. Additionally, we achieved a maximum continuous-wave mode-locked output power of 213 mW at an absorbed pump power of 8.3 W, equivalent to a pulse energy of 1.3 nJ. The RF spectrum analysis of the pulse train indicated a high SNR of nearly 70 dB, signifying excellent stability. To the best of our knowledge, This is the first report on the realization of an ultrashort pulse width mode-locked Er:Lu2O3 laser in the mid-infrared band.

Hybrid integrated GaSb/Si3N4 narrow linewidth (<50 kHz) distributed Bragg reflector laser

A narrow linewidth hybrid integrated distributed Bragg reflector (DBR) laser platform operating at 2 μm wavelength region is demonstrated. The laser architecture comprises AlGaInAsSb/GaSb type-I quantum well reflective semiconductor optical amplifiers butt-coupled to a Si3N4 photonic integrated circuit (PIC), incorporating a narrow-band DBR. The DBR is realized with a long spiral-shaped waveguide structure with periodic circular posts placed adjacent to the waveguide. At room temperature operating conditions, the laser exhibits a maximum continuous wave output power of more than 17 mW for emission near 2 μm. Linewidth properties are analyzed with a heterodyne measurement technique, involving the mixing of the laser signal with a frequency comb phase-locked to an ultra-stable laser. The hybrid laser exhibits a narrow linewidth of ∼8 kHz in 1 ms timescale and ∼50 kHz in 10 ms timescale.

Hundred-watt Ho:YAG oscillator pumped by high-power Tm:YLF laser with orthogonal cylindrical lenses spot shaping

A hundred-watt, linearly-polarized Ho:YAG oscillator, pumped by a 200 W, home-made and s-polarized Tm:YLF laser, was demonstrated. By utilizing a combination of a half-wave plate (HWP) and a thin-film polarizer (TFP), the Tm:YLF laser was split into two orthogonally polarized parts. Each part was significantly reshaped by a system of orthogonally arranged cylindrical lenses and subsequently used to dual-end pump the oscillator. With a total incident pump power of 183 W, a continuous wave (CW) output power of 101 W at 2.1 μm was achieved, with corresponding slope efficiency and optical-to-optical conversion efficiency (OOCE) of 61.6 % and 55.2 %, respectively. Additionally, the beam quality factors, measured in the x and y directions, were 1.59 and 1.35, respectively. Finally, under Q-switched operation at a repetition rate of 20 kHz, a maximum output power of 97 W was achieved, with a corresponding pulse width of less than 34 ns. The central wavelength of the laser was measured to be 2090.2 nm.

Diode-pumped dual-wavelength Nd:YVO4/Nd:CTGAS laser

LD pumped dual-wavelength lasers have great application potential in scientific and technical scopes. In this paper, we reported a novel dual-wavelength laser by combining Nd:YVO4 and Nd:CTGAS crystals. For 1064 nm and 1068 nm dual-wavelength laser operation, the maximum continuous-wave output power was 929 mW, corresponding to an optical conversion efficiency of 38.7 %. With a Cr:YAG crystal as the saturable absorber, the maximum passively Q-switched output power was 239 mW, giving a shortest pulse width of 20.8 ns and an optical conversion efficiency of 17.1 %.

Cryogenically cooled Yb:KGW oscillator

We demonstrated a cryogenically cooled Yb:KGd(WO4)2 (Yb:KGW) oscillator. At 77 K, a maximum continuous-wave (CW) output power of 10 W with an optical-to-optical efficiency of 69.4% was achieved. The tuned wavelength bandwidth was 5.9 nm at Nm-polarization and 7.7 nm at Np-polarization, which shows the potential for the broadband amplification. Mode-locked pulses were obtained at a 74.4 MHz repetition rate, where the corresponding wavelength was 1020.4 nm, with a spectral bandwidth of 0.148 nm. This is the first experimental demonstrated cryogenically cooled Yb:KGW oscillator, as far as we know.

20 W CW laser operation of Tm:YAP single crystal fiber

We report the development of a low-loss, thulium-doped yttrium aluminum perovskite (Tm:YAP) single-crystal fiber (SCF), fabricated using the Czochralski method. This SCF features undoped YAP end caps that are directly grown on both ends, aimed at improving thermal management and enhancing the guidance of pump light. This innovative design also removes differences in crystallographic orientation, exhibiting a propagation loss of 0.0112 cm−1 at 1.94 µm. When pumped by diode lasers at 788 nm, the SCF laser delivers continuous-wave output powers of 11.9 W and 20.6 W under single-end and double-end pumping configurations, respectively. The slope efficiencies achieved are 53.2 % and 40.7 %, relative to the incident pump power. To the best of our knowledge, this is the inaugural report of a Tm:YAP SCF laser.

Comparison on performances of continuous and pulsed operation in anti-misalignment laser of Er:YAG and Er:LuAG crystals

The thermal focal lengths, absorption efficiencies, and laser performances of Er:YAG and Er:LuAG crystals are systematically demonstrated within an anti-misalignment double corner-cube-prisms resonator. The maximum continuous-wave output power of 5.12 W at 1645.39 nm and 6.43 W at 1650.33 nm are obtained, with slope efficiencies of 16.29 % and 36.78 %. In pulsed operation, Er:YAG yielded a maximum pulse energy of 5.1 mJ, and Er:LuAG delivered 4.7 mJ, both at the pulse repetition rate of 200 Hz. The beam qualities, represented by M2 factors, are measured at 1.52 for Er:YAG and 1.44 for Er:LuAG.

Blue GaN-based DFB laser diode with sub-MHz linewidth

Distributed feedback laser diodes (DFBs) serve as simple, compact, narrow-band light sources supporting a wide range of photonic applications. Typical linewidths are on the order of sub-MHz for free-running III-V DFBs at infrared wavelengths, but linewidths of short-wavelength GaN-based DFBs are considerably worse or unreported. Here, we present a free-running InGaN DFB operating at 443 nm with an intrinsic linewidth of 685 kHz at a continuous wave output power of 40 mW. This performance is achieved using a first-order embedded hydrogen silsesquioxane (HSQ) surface grating. The frequency noise is measured using a cross-correlated self-heterodyne frequency discriminator, and two estimations of integrated linewidth are evaluated using 1/π integration and β-separation line integration methods.

High continuous-wave power surface emitting terahertz lasers integrated with multimode interferometer

Distributed feedback (DFB) surface emitting semiconductor laser realizes power extraction by periodic photonic heterostructure. A direct method to increase the output power is scaling up the area of active region, however, the length of the device is restricted by the coupling strength of the DFB grating. Herein we develop a high-power single-mode surface emitting scheme by monolithically integrating second-order DFB terahertz quantum cascade laser and a multimode interferometer, which can significantly enhance the optical power by increasing photon density and altering field distribution in the grating region. Application of this concept leads to high continuous-wave (CW) surface emitting power of 55 mW, with single-lobed far-field pattern and single-mode operation at about 3.9 THz, which is among the best reported results. Such an integrated scheme can be combined with any one-dimensional photonic heterostructure, which has great potential in further improving the pulsed and CW output power of single-mode semiconductor lasers.

High-efficiency and high-brightness broad area laser diodes with buried implantation current blocking

Buried-regrown-implant-structure (BRIS) technology combines two-step epitaxial regrowth with an intermediate ion implantation step in order to realise a buried current aperture close to the active region of a laser diode. In this paper we carry out a systematic performance comparison demonstrating the benefit of BRIS technology in single emitter broad-area lasers (BALs). We investigate stripe width W = 100 μ m and resonator length L = 4 mm single emitter lasers emitting at wavelength λ = 915 nm, comparing the performance of BRIS devices with different implantation depths with reference devices with only contact layer implantation. We show that using BRIS technology we achieve a continuous wave output power of 20 W at 57% efficiency, with a peak efficiency of 68%, and maintain a lateral brightness of 3.4 mm · mrad up to 19 W, improved over the reference devices due to reduced lateral current spreading in the BRIS devices. Further, we show results of ongoing aging experiments, which has shown no device degradation up to 5000 hours from BRIS devices.

4.3 µm high-power amplified spontaneous emission fiber source based on CO2-filled nested hollow-core anti-resonant fiber

We report a 4.3 µm mid-infrared (mid-IR) high-power amplified spontaneous emission (ASE) fiber source based on CO2-filled nested hollow-core anti-resonant fiber (Nested HC-ARF). The pump source is a homemade hundred-watt-level wavelength-tunable 2 µm single-frequency fiber laser. A 5.7 m long 8-tube Nested HC-ARF is used as the gas cell, with a core diameter of 110 µm and cladding diameter of 400 µm, which exhibits transmission loss of 0.1 dB/m at 2 µm and 0.24 dB/m at 4.3 µm respectively. To improve the coupling efficiency of the high-power pump laser and reduce the influence of the thermal effect at the input end of the hollow-core fiber, the fiber is designed for multimode transmission at the pump wavelength. A continuous wave output power of 6.6 W at 4.3 µm is achieved, and the slope efficiency is 17.05%. To the best of our knowledge, it is the highest output power for such gas-filled HC-ARF ASE sources in 4∼5 µm. This work demonstrates the great potential of gas-filled HC-ARF generating high-power mid-IR emission.

Wavelength-switching performance and thermal lens effect of cryogenic Yb:YAG lasers

Wavelength-switching performance and thermal lens effect of cryogenic Yb:YAG lasers pumped by a 940 nm laser diode are presented. A maximum continuous wave output power is reached 13.16 W at 80 K with an optic-optic efficiency of 25.6% at an incident pump power of 60 W. The wavelength-switching performance is observed and explained by absorbed pump power threshold behavior as temperature. Moreover, we directly characterize the thermal lens effect by wavefront measurement with a Shack-Hartmann wavefront sensor. The wavefront peak-to-valley value (PV) is 0.338 µm (about 0.33λ) at 80 K, corresponding to a thermal lens dioptric power of 0.15 m-1. The substantial decrease of the thermal lens effect contributes to the significant improvement of laser performance, which is consistent with the brilliant beam quality factor M2 of about 1.10 at both x and y directions.

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

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

High-power ultra-wideband power-combining technique based on microstrip line and ridge waveguide

ABSTRACT Based on microstrip-line power divider and ridge-waveguide power combiner, a high-power ultra-wideband solid-state power-combining amplifier is designed and fabricated. The Measured results show that the continuous wave output power of the ultra-wideband solid-state power-combining amplifier reaches over 100 W within the frequency range of 6–18 GHz, the maximum output power is nearly 200 W, the power-combining efficiency is approximately 80%, and the power-added efficiency is better than 14%.

Numerical analysis of cascade lasing in Ho:ZBLAN fiber lasers with efficient output at ∼750 nm

Recent advances in blue-emitting laser diodes (LDs) have enabled visible laser operation in rare-earth-doped fluoride fibers. Therefore, investigation of the power scaling of visible fiber lasers enabled by direct blue diode pumping is significant. In this study, we numerically investigated the performance of a continuous-wave (CW) Ho:ZBLAN fiber laser operating at approximately 750 nm for the 5F4,5S2→5I7 transition using a cascade lasing process. Direct diode pumping at 450 nm is used in conjunction with double-clad fiber geometry. Simultaneous lasing for the mid-IR 5I7→5I8 transition effectively depopulated the 5I7 level and significantly enhanced efficiency and power scalability. A slope efficiency of 49% was associated with the calculated CW output power of 14.2 W at a launched pump power of 30 W. This study demonstrates the significance of depopulating the lower laser level in the development of an efficient Ho:ZBLAN 750 nm fiber laser and offers an alternative approach for developing high-power visible laser sources.

Multi-stage coherent beam combination of semiconductor optical amplifiers in ready-made fiber couplers

We report on multi-stage coherent beam combination (CBC) of continuous-wave (CW) outputs from semiconductor optical amplifiers (SOAs) in ready-made fiber couplers. The first CBC stage combines two 120-mW outputs from SOAs seeded by an extended-cavity diode laser (ECDL) at 1458 nm in a 2×2 50%:50% fiber coupler. Two beams generated by two such CBC setups are then combined in the second stage. By concatenating three stages we obtained an output power of 723 mW at 1458 nm from eight SOAs with a total combining efficiency of 75.3%. Stable power generation without interrupts nor degradation over three days was successfully implemented using a simple low-bandwidth servo system. An averaged single-stage combining efficiency of 89.5% deduced from seven CBC setups constituting the three-stage CBC is used to estimate scaling to further stages. As a practical application the output is used to second harmonic generation (SHG) in a nonlinear crystal to achieve an output power of 239 mW at 729 nm.

Compact Diode-Pumped 946 nm Nd:YAG Laser with Good Beam Quality

A continuous-wave (CW), high-power, quasi-three-level Nd:YAG laser operating at 946 nm is reported. The beam quality of the laser is greatly improved. The laser consists of a composite Nd:YAG rod end pumped by a fiber-coupled diode laser inside a simple concave-plane cavity. At an incident pump power of 31 W, a maximum CW output of 9.98 W was obtained at 946 nm, with a beam quality factor of M2~5. The corresponding optical-to-optical efficiency was 32.2% with respect to the incident pump power. To the best of our knowledge, this is the highest output power at 946 nm with such a beam quality ever generated by diode-pumped Nd:YAG laser with bulk crystals.

Continuous-wave and SESAM mode-locked operation of a Yb:YSr3(PO4)3 laser.

We report on the continuous-wave (CW) and, for what we believe to be the first time, passively mode-locked (ML) laser operation of an Yb3+-doped YSr3(PO4)3 crystal. Utilizing a 976-nm spatially single-mode, fiber-coupled laser diode as pump source, the Yb:YSr3(PO4)3 laser delivers a maximum CW output power of 333 mW at 1045.8 nm with an optical efficiency of 55.7% and a slope efficiency of 60.9%. Employing a quartz-based Lyot filter, an impressive wavelength tuning range of 97 nm at the zero level was achieved in the CW regime, spanning from 1007 nm to 1104 nm. In the ML regime, incorporating a commercially available semiconductor saturable absorber mirror (SESAM) to initiate and maintain soliton-like pulse shaping, the Yb:YSr3(PO4)3 laser generated pulses as short as 61 fs at 1062.7 nm, with an average output power of 38 mW at a repetition rate of ∼66.7 MHz.