Diffraction-limited Beam Quality Research Articles

9-W Output Power From an 808-nm Tapered Diode Laser in Pulse Mode Operation With Nearly Diffraction-Limited Beam Quality

808-nm tapered diode lasers are fabricated based on a super-large optical-cavity (SLOC) structure with very small divergence of 18deg full width at half-maximun (FWHM). A 16-W overall output power with 9 W of nearly diffraction-limited beam quality in pulse mode operation is obtained.

Simultaneous direct amplification and compression of picosecond pulses to 65-kW peak power without pulse break-up in erbium fiber

Picosecond pulses at 1.56 micro mm wavelength are directly amplified with a diffraction limited beam quality in a core-pumped Er fiber with an 875 micro m(2) effective area. The interplay between nonlinear spectral broadening and anomalous fiber dispersion compresses the input pulse duration during amplification so that 42 nJ energy pulses with approximately 65 kW peak power are achieved without pulse break-up.

Generation of hard X-rays using an ultrafast fiber laser system

We report the first hard X-ray source driven by a femtosecond fiber laser. The high energy fiber CPA system incorporated a 65mum LMA fiber amplifying stage which provided 300-fs recompressed pulses and diffraction limited beam quality with M(2) < 1.07. A deformable mirror was used to optimize the wavefront and the spot size was focused down to 2.3 mum with an f/1.2 paraboloidal mirror. 50muJ was deposited on the nickel target with 2x10(15)-W/cm(2) focal intensity and a distinctive Ni K(alpha)-line (7.48 keV) emission was measured with 5x10(-8) energy conversion efficiency.

Power scaling of semiconductor laser pumped Praseodymium-lasers

We report on efficient lasing of Pr-doped fluoride materials with cw output powers up to 600 mW in the visible spectral range. Praseodymium doped LiYF(4) and LiLuF(4) crystals were pumped either by an intracavity frequency doubled optically pumped semiconductor laser with output powers up to 1.6 W and nearly diffraction limited beam quality or by a multimode GaN-laser diode with an output power of about 370 mW. Furthermore, intracavity frequency doubling of the red Pr-laser radiation to 320 nm reaching output powers of more than 360 mW with a conversion efficiency of 61% and an optical-to-optical efficiency of 22% are presented.

Composite Yb:YAG/Cr^4+:YAG ceramics picosecond microchip lasers

Efficient laser-diode pumped picosecond self-Q-switched all-ceramic composite Yb:YAG/Cr(4+):YAG microchip lasers with 0.72 MW peak power has been developed. Lasers with nearly diffraction-limited beam quality (M(2) < 1.09), oscillate at stable single- and multi- longitudinal-modes due to the combined etalon effects in the Yb:YAG and Cr(4+):YAG parts of its binary structure.

High Power Femtosecond Fiber Chirped Pulse Amplification System for High Speed Micromachining

The need for improved precision in a wide variety of micromachining applications has driven scientific interest in ultrashort pulse lasers. Despite numerous demonstrations of reduced heat effect and improved processing quality, the utility of such lasers has been limited by the heavy demands placed upon laser performance. In addition to high contrast laser pulses with minimal pulse-to-pulse fluctuation, an ultrashort pulse laser must provide near diffraction-limited beam quality and robust long-term laser operation with high repetition rate for high processing speeds. We report here on a research prototype, high power femtosecond fiber chirped pulse amplification system. The system produces compressed pulses with energies >50 µJ at >15 W with M 2 1000:1 temporal contrast despite significant self-phase modulation during amplification corresponding to a nonlinear phase delay of ~6π. As a demonstration of high speed femtosecond micromachining, we drill and cut 0.5-mm thick metal, semiconductor and dielectric targets.

Subnanosecond diode-pumped passively Q-switched Nd:GdVO4 laser with peak power &amp;gt;1MW

The authors report on a passively Q-switched diode-pumped Nd:GdVO4 miniature laser generating 0.5mJ pulses at 1063nm, with 420ps time duration and 1.2MW peak power, at a repetition rate up to 200Hz and with a nearly diffraction-limited beam quality (M2≈1.1).

The HALNA project: Diode-pumped solid-state laser for inertial fusion energy

High-enery, rep.-rated, diode-pumped solid-state laser (DPSSL) is one of leading candidates for inertial fusion energy driver (IFE) and related laser-driven high-field applications. The project for the development of IFE laser driver in Japan, HALNA (High Average-power Laser for Nuclear Fusion Application) at ILE, Osaka University, aims to demonstrate 100-J pulse energy at 10 Hz rep. rate with 5 times diffraction limited beam quality. In this article, the advanced solid-state laser technologies for one half scale of HALNA (50J, 10 Hz) are presented including thermally managed slab amplifier of Nd:phosphate glass and zig-zag optical geometry, and uniform, large-area diode-pumping.

Diffraction analysis of aberrated laser resonators

A numerical analysis of laser resonators with aberrations is presented. The analysis shows that aberrations lead to large diffraction losses of laser resonators which are laid out to produce diffraction-limited beam quality. Static or dynamic compensation of the aberrations is possible and would yield much higher output power.

Ultrafast high power fiber laser systems

Fiber laser systems offer unique properties for the amplification of ultrashort pulses to high powers. Two approaches are discussed, the amplification of linearly chirped parabolic pulses and a fiber based chirped pulse amplification system. Using the first method, we succeeded to generate 17-W average power of linearly chirped parabolic pulses at 75 MHz repetition rate and diffraction-limited beam quality in a large-mode-area ytterbium-doped fiber amplifier. The recompression of these pulses with an efficiency of 60% resulted in 80-fs pulses with a peak power of 1.7 MW. Furthermore, we report on a diode-pumped ytterbium-doped double-clad fiber based chirped pulse amplification system delivering 220-fs pulses, at 1040 nm wavelength, 73 MHz repetition rate and up to 131 W average power, corresponding to a peak power of 8 MW. Key element is a diffraction grating compressor consisting of highly efficient transmission gratings in fused silica allowing the recompression at this high power. To cite this article: J. Limpert et al., C. R. Physique 7 (2006).

High-power ultrafast fiber laser systems

The recent demonstration of rare-earth-doped fiber lasers with a continuous wave output power well above the kilowatt level with diffraction-limited beam quality has proven that fiber lasers constitute a power-scalable solid-state laser concept. To generate intense pulses from a fiber, several fundamental limitations have to be overcome. Nevertheless, novel experimental strategies and fiber designs offer an enormous potential toward laser systems with high average powers and high pulse energies. This paper reviews the challenges, achievements, and perspectives of ultrashort pulse generation and amplification in fibers.

High-power 808-nm tapered diode lasers with nearly diffraction-limited beam quality of M/sup 2/=1.9 at P=4.4 W

High-power 808-nm tapered diode lasers mounted as single emitters with very good brightness were manufactured and analyzed. The beam propagation ratio M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> is 1.9 at 4.4 W; a very low beam propagation ratio M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 1.3 is achieved at 3.9 W. At 808 nm, the high brightness of 460 MWmiddotcm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> sr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> never reported before is a step forward toward new applications of tapered diode lasers

High-Power fiber amplifier with widely tunable repetition rate, fixed pulse duration, and multiple output wavelengths

We report a pulsed, fiber-amplified microchip laser providing widely tunable repetition rate (7.1 - 27 kHz) with constant pulse duration (1.0 ns), pulse energy up to 0.41 mJ, linear output polarization, diffraction-limited beam quality (M(2) < 1.2), and < 1% pulse-energy fluctuations. The pulse duration was shown to minimize nonlinear effects that cause temporal and spectral distortion of the amplified pulses. This source employs passive Q-switching, single-stage single-pass amplification, and cw pumping, thus offering high efficiency, simplicity, and compact, rugged packaging for use in practical applications. The high peak power and high beam quality make this system an ideal pump source for nonlinear frequency conversion, and we demonstrated efficient harmonic generation and optical parametric generation of wavelengths from 213 nm to 4.4 mum with Watt-level output powers.

300?W quasi-continuous-wave diffraction-limited output from a diode-pumped Nd:YAG master oscillator power amplifier with fiber phase-conjugate stimulated Brillouin scattering mirror

A master oscillator power amplifier system comprising a cw Nd:YAG master oscillator, a quasi-cw diode-pumped power amplifier, and a fiber-based stimulated Brillouin scattering phase-conjugate mirror is reported. A 12-pass amplifier configuration is employed to achieve high gain in a small-length slab amplifier. Residual and pump-induced optical inhomogeneities in the slab are corrected by the fiber phase conjugator to achieve diffraction-limited output beam quality. 300 W quasi-cw output and a maximal attainable gain of approximately 150 for the system are obtained.

The renaissance and bright future of fibre lasers

The first rare-earth-doped fibre lasers were operated in the early 1960s and produced a few milliwatts at a wavelength around 1 µm. For the next several decades, fibre lasers were little more than a low-power laboratory curiosity. Recently, however, fibre lasers have entered the realm of kilowatt powers with diffraction-limited beam quality. In this paper we review the reasons for this power evolution. Beyond this, we will discuss how the next generation of fibres, so-called photonic crystal fibres, enable upward power scaling and therefore open up the avenue to new performance levels of solid-state lasers.

LD side-pumped passively Q-switched Yb:YAG slab laser

A quasi-continuous wave laser diode side-pumped passively Q-switched Yb:YAG slab laser with Cr 4+:YAG saturable absorber has been demonstrated in order to understand the pulse properties of Yb:YAG crystal. To our knowledge the maximum 69% extraction efficiency is achieved by the system. 44 μJ pulse energy and 1.64 KW peak power with near diffraction-limited beam quality are presented at 25 Hz repetition rate. The build-up time of the Q-giant in the passively Q-switched laser is shown.

Micro- and Nano-Structured Optical Fibers - Artificial Media for Amplification of Light.

ABSTRACTIn experiments with rare-earth-doped fibers impressively results have been demonstrated and shown that fiber lasers and amplifiers are an attractive and power scalable solid-state laser concept. With ytterbium-doped large-mode-area double-clad fibers, output powers approaching the kW-range with diffraction limited beam quality have been realized in the continuous regime. Also in the pulsed regime, even for femtosecond pulse duration average output powers in the range of 100 W have been demonstrated. Further power scaling is limited by the end facets damage, thermo-optical problems or nonlinear effects. To overcome these restrictions microstructured fibers can be used. This type of fibers has several new preferable features. In our contribution we will discuss the advantages of microstructured fibers to reduce nonlinear effects inside the fiber and the possibility to scale the output power of fiber lasers and amplifiers with excellent beam quality. We also show fiber based chirped pulse amplification system (CPA-System) with ultra short pulses, pulse energies of up to 100 μJ and high repetition rates.

Ytterbium-doped large-core fiber laser with 1.36 kW continuous-wave output power

We have demonstrated a highly-efficient cladding-pumped ytterbium-doped fiber laser generating 1.36 kW of continuous-wave output power at 1.1 mum with 83% slope efficiency and near diffraction-limited beam quality. The laser was end-pumped through both fiber ends and showed no evidence of roll-over even at the highest output power, which was limited only by available pump power.

Ytterbium-doped large-core fibre laser with 610 W of near diffraction-limited output power

A cladding-pumped ytterbium-doped fibre laser, generating up to 610 W of continuous-wave output power at 1.1 µm with slope efficiency of 80% and near diffraction-limited beam quality (M2=1.3) is reported. No undesirable roll-over was observed in output power with increasing pump power.

100-W single-frequency master-oscillator fiber power amplifier.

We report the efficient generation of 100-W single-frequency radiation with diffraction-limited beam quality at the 1064-nm wavelength by use of a master-oscillator fiber power-amplifier system, consisting of a diode-pumped monolithic nonplanar ring laser as the master oscillator and an Yb-doped large-mode-area fiber as the power amplifier. The emission spectrum, the intensity noise behavior, and further power-scaling possibilities to the >200-W level, which are determined by the threshold of stimulated Brillouin scattering in the fiber amplifier, are discussed.