High-power Single-frequency Research Articles

Detailed performance modeling of a pulsed high-power single-frequency Ti:sapphire laser

Differential absorption lidar (DIAL) is a unique technique for profiling water vapor from the ground up to the lower stratosphere. For accurate measurements, the DIAL laser transmitter has to meet stringent requirements. These include high average power (up to 10 W) and high single-shot pulse energy, a spectral purity >99.9%, a frequency instability <60 MHz rms, and narrow spectral bandwidth (single-mode, <160 MHz). We describe extensive modeling efforts to optimize the resonator design of a Ti:sapphire ring laser in these respects. The simulations were made for the wavelength range of 820 nm, which is optimum for ground-based observations, and for both stable and unstable resonator configurations. The simulator consists of four modules: (1) a thermal module for determining the thermal lensing of the Brewster-cut Ti:sapphire crystal collinear pumped from both ends with a high-power, frequency-doubled Nd:YAG laser; (2) a module for calculating the in-cavity beam propagations for stable and unstable resonators; (3) a performance module for simulating the pumping efficiency and the laser pulse energy; and (4) a spectral module for simulating injection seeding and the spectral properties of the laser radiation including spectral impurity. Both a stable and an unstable Ti:sapphire laser resonator were designed for delivering an average power of 10 W at a pulse repetition frequency of 250 Hz with a pulse length of approximately 40 ns, satisfying all spectral requirements. Although the unstable resonator design is more complex to align and has a higher lasing threshold, it yields similar efficiency and higher spectral purity at higher overall mode volume, which is promising for long-term routine operations.

A High Power Single Frequency Diode Side-Pumped Nd:YAG Ring Laser

We demonstrate a high-power single-frequency diode-side pumped Nd:YAG laser at 1064 nm. A bow-tie ring cavity configuration comprising two plane and two curved mirrors with two-rod birefringence compensation is employed. The influence of length Lx between two curved mirrors on output power and beam quality is investigated theoretically and experimentally while the separation of the flat mirrors is set to be 656 mm and the fold angle is 10°. When the pump powers are 358, 343 and 329 W at 808 nm, the maximal output powers of 31.9, 26 and 14.1 W are obtained with beam quality factors M2 = 1.41, 1.12 and 1.20 for Lx = 205, 215 and 230 mm, respectively.

High-Power Low-Noise Nd:YAP/LBO Laser With Dual Wavelength Outputs

A high-power single-frequency Nd:YAP/LBO laser with stable dual wavelength outputs is designed and built. The laser resonator satisfying optimal coupling condition for second-harmonic generation is in a configuration of a figure “8” shaped ring cavity consisting of two convex mirrors and two concave mirrors. An additional wedge YVO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystal is inserted in the resonator to act as a polarizer, so that the stability of the laser operation is improved. The maximum output powers of 4.5 W at 540 nm and 1.5 W at 1080 nm are simultaneously achieved. The measured power stabilities of the fundamental wave and the second-harmonic wave are ±0.32% and ±0.6% for 3 h, respectively.

High-Power Single-Frequency Thulium-Doped Fiber DBR Laser at 1943 nm

We report on a high-power single-frequency mode-hop-free fiber distributed Bragg reflector (DBR) laser fabricated from Tm-doped photosensitive alumino-silicate fiber and in-band pumped by an Er/Yb fiber laser at 1565 nm. The fiber DBR laser yielded up to 580 mW of single-frequency single-ended output at 1943 nm for ~ 5 W of absorbed pump power. Further scaling of the DBR laser output power was achieved with the aid of a simple Tm-doped fiber amplifier stage spliced directly to the DBR fiber without the need of an optical isolator. The maximum output power from the DBR laser and fiber amplifier was 2.9 W for a combined absorbed pump power of 9 W. The merits of this DBR laser architecture compared to conventional DBR and distributed-feedback laser configurations are discussed.

高功率单频线偏振掺镱全光纤放大器

We report an all-fiber high power, single frequency large-mode area (LMA) linearly polarized ytterbiumdoped fiber amplifiers (YDFA) module, which is based on the master oscillator multi-stage power amplifiers (MOPA). The maximum output power is 43.8 W at a wavelength of 1064 nm when 60-W launched pump light is coupled, with high slope efficiency of 88%, polarization extinction rate (PER) >17.2 dB and nearly diffraction-limited beam quality (M2<1.1).

高功率单频线偏振掺镱全光纤放大器

高功率单频线偏振掺镱全光纤放大器

All-fiber, high power single-frequency linearly polarized ytterbium-doped fiber amplifier

All-fiber, high power single-frequency linearly polarized ytterbium-doped fiber amplifier

掺镱光纤放大器中的热效应分析

In order to study Stimulated Brillouin Scattering(SBS) in Yb3+-doped double clad single-frequency fiber amplifier,thermal effects of the fiber amplifier were analyzed theoretically,based on the rate equations and heat transfer equations.The impacts of the fiber temperature,which can broaden the SBS gain profile and suppress SBS,on the amplifier performances were discussed.The relationships between the SBS and pump power,signal power,heat transfer coefficient were simulated.The results of simulation provide theoretical guide to optimum design of high power single-frequency fiber amplifier.

22 瓦高功率全光纤单频MOPA激光器

We demonstrate a high-power single-frequency master oscillator power amplifier (MOPA) fiber laser. The central wavelength of the single-frequency fiber laser seed is 1 063.8 nm, with a linewidth narrower than 20 kHz and output power of 120 mW. By using two-stage amplification, a single-frequency fiber laser with an output power of 122 W is obtained, and the optical-optical conversion efficiency is 72%. No significant amplified spontaneous emission (ASE) or stimulated Brillouin scattering (SBS) is observed. The output power can be further increased by launching more pump power.

Limits of Stimulated Brillouin Scattering Suppression in Optical Fibers With Transverse Acoustic Waveguide Designs

A major approach investigated recently for stimulated Brillouin scattering (SBS) suppression in fiber amplifiers for high power single frequency fiber lasers is to explore designs of acoustic waveguide in optical fibers. This acoustic waveguide can be implemented to some extent independent of the optical waveguide by using a combination of dopants which modify the host glass by varying levels in acoustic and optical properties. Although this approach provides some SBS suppressions, the new analysis described in this work, considering the often omitted leaky acoustic modes, demonstrates its limit. A complex acoustic mode solver, reported in details elsewhere, was recently developed to find solutions for simultaneous longitudinal and shear acoustic wave equations which satisfy rigorous boundary conditions in an arbitrary circular acoustic waveguide. By taking advantage of this new tool, it is possible to find the leaky acoustic modes for acoustic waveguides designed for SBS suppressions. In these acoustic waveguides, the guided acoustic modes often have a reduced overlap with the optical modes by design and, sometimes, do not exist at all, while the leaky acoustic mode can have a significant stronger overlap with the optical modes and, consequently, can play a dominant role in the SBS gain spectrum. It is, therefore, critical to consider the leaky acoustic modes in these cases. Two prominent transverse acoustic waveguide designs proposed recently for SBS suppression in optical fibers are studied here. This work reports, for the first time, the limits of these designs for SBS suppression. With consideration of the leakage acoustic modes, some new insights are provided on the underlying physics as well as on how to optimize these designs for optimal SBS suppression.

High-power linearly-polarized single-frequency thulium-doped fiber master-oscillator power-amplifier

We report a high power narrow-linewidth source at approximately 2 microm based on a Tm-doped fiber distributed-feedback master-oscillator and three Tm fiber amplifier stages. The master-oscillator and first two amplifier stages were in-band pumped by Er,Yb fiber lasers operating at 1565 nm, and the final stage amplifier was cladding-pumped at 795 nm by two spatially-combined diode-stacks. The MOPA yielded 100 W of single frequency output at 1943 nm with a beam propagation factor (M(2)) of 1.25 and with a polarization extinction ratio of >94%. The output power was limited by thermally-induced damage in the final amplifier stage. The prospects for further power scaling are considered.

High power narrow linewidth single-frequency line-polarized fiber amplifier based on master-oscillator power amplifier technology

High power single-frequency (SF) lasers are of great significance in science, industry, and defense applications such as gravitational wave detection, free apace optical communication, range finding, lidar, parametric wavelength conversion in resonant cavities. We report on a high power single-frequency linearly polarized radiation with a nearly diffraction-limited beam quality by use of a two-stage fiber master-oscillator power amplifier system. The master oscillator is an SF distribution feedback fiber laser with polarization maintaining (PM) and single mode (SM) fiber pigtailed output power of about 10 mW at 1064 nm, and its line-width is of 20 kHz. This light power is amplified to about 1 W by the first stage of all-fiber SM/PM amplifier and then seeded at the second stage of high power main amplifier with large mode area (LMA) ytterbium-doped fiber (YDF). The pumping diode laser of the main amplifier is fiber-coupled (the core diameter is 400 μm and corresponding numerical aperture is 022) with a max emitting power as high as 190 W at 976 nm. By employing the co-pump configuration with a space coupling efficiency of about 85%, we demonstrate that the power output from the LMA/PM YDF (core diameter is 20 μm, inner cladding diameter is 400 μm) reaches 128 W and its corresponding overall slope-efficiency is 85% of the launched pump power. The beam profile is diffraction-limited and linearly polarized with a polarization extinction ratio over 12 dB. There is observed neither amplified spontaneous emission nor stimulated Brillouin scattering phenomenon, which means that the substitution of the pump source with the more powerful one can further enhance power output if LMA YDF with a larger core size, shorter fiber length and higher doping efficiency is used.

高功率单频主振荡光纤功率放大器研究进展

高功率单频主振荡光纤功率放大器研究进展

Single-frequency phosphate glass fiber laser with 100-mW output power at 1535 nm and its polarization characteristics

We demonstrate a high power single-frequency fiber laser. By using phosphate glass fiber as its gain media, the laser can achieve high output power of 100 mW in centimeter-long linear cavity. Single-frequency single-polarization operation with <5 kHz linewidth and 65-dB signal-to-noise ratio (SNR) is realized by using external cavity polarization feedback technology.

高功率单频光纤放大器中温度分布对受激布里渊散射的影响

高功率单频光纤放大器中温度分布对受激布里渊散射的影响

Comprehensive Modeling of Single Frequency Fiber Amplifiers for Mitigating Stimulated Brillouin Scattering

A universal model capable of handling various operating conditions has been developed for designing of high power single frequency fiber amplifiers. The model analyzes the impacts of pump configurations, fiber lengths, and fiber temperatures on amplifier performance. It shows that counter-pumped amplifiers are capable of generating several times more output than co-pumped amplifiers. To fully take their advantages and deliver the laser output, a delivery fiber should be properly designed to avoid unwanted SBS which can significantly undermine the amplifier performance. On the other hand, for applications requiring delivery fiber at relative low power, the co-pumped amplifier can be an alternative since it can use the gain fiber as the delivery fiber and thus eliminate requiring an additional delivery fiber. The model also analyzes possible approaches for suppressing SBS, such as applying additional heating, the use of SBS suppressing fiber, and increasing core diameter. It shows that applying additional heating to a co-pumped amplifier can increase the output by a factor of 1.7. Finally, the model concludes that a single frequency amplifier can achieve multiple kilowatts output by carefully choosing amplifier design and utilizing SBS suppression technique.

High power single–frequency continuously–tunable compact extended–cavity semiconductor laser

We demonstrate high power high efficiency (0:3 W) low noise single frequency operation of a compact extended-cavity surface-emitting-semiconductor-laser exhibiting a continuous tunability over 0:84 THz with high beam quality. We took advantage of thermal lens-based stability to develop a short (< 3 mm) plano-plano external cavity without any intracavity filter. The structure is optically pumped by a 1 W commercial 830 nm multimode diode laser. No heat management was required. We measured a low divergence circular TEM(00) beam at the diffraction limit (M(2) < 1:05) with a linear light polarization (> 37 dB). The side mode suppression ratio is 60 dB. The free running laser linewidth is 850 kHz limited by pump induced thermal fluctuations. Thanks to this high-Q external cavity approach, the frequency noise is low and the dynamics is in the relaxation-oscillation-free regime, exhibiting a low intensity noise, with a cutoff frequency approximately 250 MHz above which the shot noise level is reached. We show that pump properties define the cavity design and laser coherence.

Narrowband Pulsed THz Source Using Eyesafe Region Fiber Lasers and a Nonlinear Crystal

We report a high-power single-frequency fiber laser system in the eyesafe wavelength region that pumps a GaSe crystal through difference frequency generation, producing narrowband terahertz (THz). Two single-frequency continuous-wave fiber seed lasers are modulated, then amplified with a three-stage single-mode amplifier. The resulting pulses are transform-limited and high power, producing a peak THz power of 26.4 mW with narrow linewidth. This is significantly higher than earlier THz sources based on narrowband fiber lasers in the eyesafe region.

Brillouin scattering spectra in high-power single-frequency ytterbium doped fiber amplifiers

We report on theoretical and experimental investigations on spontaneous and stimulated Brillouin scattering during operation of a high-power single-frequency polarization-maintaining ytterbium doped fiber amplifier. For different amplifier configurations with co- and counter-propagating seed and pump radiation the evolution of Brillouin scattering spectra was investigated with a heterodyne detection scheme. Spontaneous Brillouin gain spectra at low powers were additionally investigated using a pump-probe technique. The data obtained from these experiments have been compared with a theoretical model based on coupled intensity equations. A Brillouin scattering suppression has been investigated theoretically and experimentally with externally applied temperature gradients along the fiber resulting in up to 3.5 dB suppression and 115 W of amplifier output power.

High peak power single frequency pulses using a short polarization-maintaining phosphate glass fiber with a large core

We report a high power, single frequency 1.5μm pulsed fiber master oscillator-power amplifier laser source using a large core, polarization-maintaining phosphate glass fiber. The phosphate glass fiber produces high powers with low nonlinearities using high Er–Yb codoping and short length. Using this fiber, we were able to generate single frequency pulses with peak powers up to 51.5kW. This is the highest reported peak pulse power for eye safe single frequency fiber laser systems.