This paper presents the results of welding tests performed with a 1kW blue laser to determine the power and spot characteristics necessary to be able to perform all the welds required in a battery and battery pack. The results of this study indicate that a minimum of 1,500 Watts with a nominal beam parameter product of 11 mm-mrad is required to interface with a scanner and achieve all of the welds required by this application. Several other key industrial applications are discussed, and the welding performance is characterized for various materials. These results are used to define the optimum laser system parameters to serve a broad range of applications. A new blue laser product architecture is presented that is capable of scaling to multi-kW power levels in order to meet the target performance. The building block for this architecture is a 400-Watt blue laser module. These units can be combined to produce systems of any power level in 400- Watt increments with excellent beam quality. The 1,500-Watt product being developed has a beam parameter product of less than 17 mm-mrad.
We developed a cryogenically cooled Yb:YAG laser as the pump beam for a pulsed Raman laser based on CVD grown
diamond crystals. The Q-switched cryogenic Yb-doped YAG 1030 nm pump laser delivered 340 W at 40 kHz with
diffraction-limited beam quality, with an optical efficiency of 80%. The record average power of 24.5 W was generated
from the Raman laser at 1193 nm. Modeling of the performance confirmed the corresponding Raman gain coefficient,
13.5 cm/GW. The laser was operated at room temperature and under cryogenic cooling at 77 K, with equal performance.
Sandia National Laboratories' program in high-power fiber lasers has emphasized development of enabling technologies
for power scaling and gaining a quantitative understanding of fundamental limits, particularly for high-peak-power,
pulsed fiber sources. This paper provides an overview of the program, which includes: (1) power scaling of diffraction-limited
fiber amplifiers by bend-loss-induced mode filtering to produce >1 MW peak power and >1 mJ pulse energy
with a practical system architecture; (2) demonstration of a widely tunable repetition rate (7.1-27 kHz) while
maintaining constant pulse duration and pulse energy, linear output polarization, diffraction-limited beam quality, and
<1% pulse-energy fluctuations; (3) development of microlaser seed sources optimized for efficient energy extraction; (4)
high-fidelity, three-dimensional, time-dependent modeling of fiber amplifiers, including nonlinear processes; (5)
quantitative assessment of the limiting effects of four-wave mixing and self-focusing on fiber-amplifier performance; (6)
nonlinear frequency conversion to efficiently generate mid-infrared through deep-ultraviolet radiation; (7) direct diode-bar
pumping of a fiber laser using embedded-mirror side pumping, which provides 2.0x higher efficiency and much
more compact packaging than traditional approaches employing formatted, fiber-coupled diode bars; and (8)
fundamental studies of materials properties, including optical damage, photodarkening, and gamma-radiation-induced
We report on the pulse shape of an actively Q-switched fiber laser. This master oscillator power amplifier architecture
generates pulses with multiple peaks due to its intrinsic dynamics. Modeling and experimental results provide us a
detailed understanding of the relative importance of the different time constants on the dynamics of the laser, which
allows us to define optimized design parameters that lead to smooth and controlled pulse shapes. This solution is simple
and robust; operation over a broad range of repetition rate and output power is achieved without any adjustment of the
laser settings, and the corresponding variation of the optical performances is minimal.
We summarize the performance of mode-filtered, Yb-doped fiber amplifiers seeded by microchip lasers with
nanosecond-duration pulses. These systems offer the advantages of compactness, efficiency, high peak power,
diffraction-limited beam quality, and widely variable pulse energy and repetition rate. We review the fundamental limits
on pulsed fiber amplifiers imposed by nonlinear processes, with a focus on the specific regime of nanosecond pulses.
Different design options for the fiber and the seed laser are discussed, including the effects of pulse duration,
wavelength, and linewidth. We show an example of a microchip-seeded, single-stage, single-pass fiber amplifier that
produced pulses with 1.1 MW peak power, 0.76 mJ pulse energy, smooth temporal and spectral profiles, diffractionlimited
beam quality, and linear polarization.
We have developed a single-emitter multi-mode laser-diode-pump platform for high efficiency, brightness and high
reliability in a small form factor. This next-generation package is scalable to higher optical power and offers a low-cost
solution for industrial applications, such as fiber lasers, graphic arts and medical. The pump modules employ high
coupling efficiency, >90%, high power-conversion efficiency, >50%, and low thermal resistance, 2.2°C/W, in an
electrically-isolated package. Output powers as high as 18W have been demonstrated, with reliable operation at 10W
CW into 105μm core fiber. Qualification results are presented for 0.15NA and 0.22NA fiber designs.
We present an experimental and theoretical analysis of four-wave-mixing (FWM) in nanosecond pulsed fiber amplifiers
FWM leads to a saturation of the in-band amplified pulse energy and to distortions of the spectral and temporal profiles,
and it is the main limiting effect in the ~1 ns temporal regime. A simple model considering both Raman and FWM
contributions provides a good description of the measured behaviours, allowing optimization and design tradeoffs to be
explored for mitigating FWM.
We report a pulsed, Nd:YAG (1064 nm) microchip laser amplified by a mode-filtered, Yb-doped fiber amplifier. The
system provided a 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, and <1% pulse-energy fluctuations. Detailed
spectral and temporal characterization of the output pulses revealed the effects of four-wave mixing and stimulated
Raman scattering, and we investigated the effects of fiber length and Yb-doping level on system performance. The
amplifier output was efficiently converted to a variety of wavelengths between 213 and 4400 nm by harmonic generation
and optical parametric generation, with Watt-level output powers. The laser system employs a simple architecture and is
therefore suitable for use in practical applications.