The laser performance of a resonantly pumped Er3+:YAG solid-state heat-capacity laser (SSHCL) as an eye-safe
high-power laser was investigated experimentally and theoretically using a new analytical quasi-three-level laser
model as well as a fully numerical thermo-optical model. While the analytical model is based on a new spectral
theory that can predict the thermal evolution of the peak absorption and emission cross-sections for pump
and laser transition in a simple mathematical form, the numerical model takes into account the full spatially
resolved temperature dependence of the most important parameters of the gain medium like thermo-mechanical
parameters (e.g. heat conduction and specific heat), spectroscopic and multiphonon-relaxation lifetimes of the
first four manifolds and the full spectrally resolved information of emission and absorption (4I15/2
as well as exited-state absorption and re-emission (4I13/2
↔4I9/2). In the experiments up to 76 W of peak
output power could be achieved with a slope efficiency of 39%. The laser could be operated for about 2 s
with an integrated output energy of 55 J, currently limited by the available pump power with respect to the
temperature-dependent threshold. Cavity parameters like internal losses (approximately 3.6%) and a mode-fill efficiency of up
to 79% were also derived as well as the effective medium energy storage lifetime caused by fluorescence radiation
trapping. The experimental data are compared with the models of the diode-pumped Er3+:YAG SSHCL with
We have measured upconversion fluorescence resulting from the excitation of room temperature 1% and
5% Er:YAG by a 1532 nm nanosecond pump source. Measurements of the fluorescence decay from the
4S3/2 manifolds to the 4I15/2 ground state manifold were observed over a wide range of
excitation pulse fluence values. A unique set of upconversion parameters were extracted from the
measurements using a modification of the traditional rate equation model. Results of calculation are
compared to measurement.
Growing interest to high power lasers in the eye-safe spectral domain initiated a new
wave of activity in developing solid-state lasers based on bulk
Er3+-doped materials. The
resonant pumping of SSL allows for shifting significant part of thermal load from gain
medium itself to the pump diodes, thus greatly reducing gain medium thermal distortions
deleterious to SSL power scaling with high beam quality. The two major resonant
pumping bands in Er:YAG are centered around 1470 and 1532 nm. Pumping into
each of these bands has its pros and contras. The best approach to resonant pumping of
Er:YAG active media in terms of pump wavelength is yet to be determined.
We report the investigation results of high power diode-pumped Er:YAG laser aimed at
direct comparison of resonant pumping at 1470 and 1532 nm. Two sources used for
pumping were: 1530-nm 10-diode bar stack (>300 W CW) and 1470-nm
stack (>650 W CW). Both pumps were spectrally narrowed by external volume Bragg
gratings. The obtained spectral width of less than 1 nm allowed for 'in-line' pumping of
Er3+ in either band. The obtained CW power of over 87 W is, to the best of our
knowledge, the record high power reported for resonantly pumped Er:YAG DPSSL at
We are investigating materials for direct blue solid-state lasers assuming UV excitation with GaN based laser diodes.
Room temperature spectroscopy is reported relevant to a proposed quasi-three level laser from the 4F9/2 level in trivalent
dysprosium. Modeling based on these measurements suggests this is a promising new laser transition.
We report on a novel electronically controlled active heat sink for high-power laser diodes offering
unparalleled capacity in high-heat flux handling and temperature control. The heat sink receives diode
waste heat at high flux and transfers it at reduced flux to environment, coolant fluid, heat pipe, or structure.
Thermal conductance of the heat sink is electronically adjustable, allowing for precise control of diode
temperature and the diode light wavelength. When pumping solid-state or alkaline vapor lasers, diode
wavelength can be precisely temperature-tuned to the gain medium absorption features. This paper presents
the heat sink physics, engineering design, and performance modeling.
Even though Yb-doped fiber lasers are known to be the most powerful and most
efficient among all fiber lasers, recent successes in the eye-safe ~1.5μm Yb-Er-doped
fiber lasers (where Er is excited through Yb-Er energy transfer) are quite impressive.
Output power of Yb-Er fiber lasers reached ~300 W level and their optical-to-optical
efficiency, for somewhat lower power levels, is exceeding 40% . Nevertheless, as far
as real eye safety is concerned, multi-hundred Watt Yb-Er fiber lasers typically carry in
their output a significant fraction of competing 1-μm Yb emission, which totally
compromises an eye-safe side of the application. Ultimate efficiency and thermal
management of Yb-Er approach are also suffering due to: (i), inefficiency of Yb-Er
energy transfer and, (ii), gigantic ~40% quantum defect of Er-doped fiber pumped at
Presented here are very recent and successful results on power scaling of
resonantly pumped Yb-free Er-doped fiber lasers and amplifiers. We are reporting an Ybfree
Er-doped cladding-pumped fiber power scaling to ~50 W with ~57% optical-tooptical
efficiency  in a few first experimental steps. This is clear manifestation of
scaling potential of this most efficient approach to high power
eye-safe fiber laser. The
only competing approach to scalable eye-safe fiber laser implements
pumped at ~790 nm while relying on well known "2-for-1" process leading to quite
efficient excitation of the ~2μm Tm3+ laser operation . This approach has operational
optical-to-optical efficiency quantum limit of ~75% , while resonantly pumped Ybfree
Er-doped fiber laser's optical-to-optical efficiency quantum limit exceeds 95% due
to its low-quantum-defect (QD) pump-lase scheme. Significant scaling potential of
resonantly-pumped Yb-free Er-doped fiber lasers and amplifiers sets a path to an eye-safe
fiber laser concept with drastically relaxed thermal management and nearly diffraction
limited beam quality at ~kW-=-class power levels as well as high electrical to optical
We have designed and developed a grating based thulium (Tm) doped fiber laser with ~150 nm tuning range which is
used as the master oscillator in a master oscillator power amplifier (MOPA) thulium fiber laser system. Due to thermal
instability in the grating used for tuning, the MO could produce a power up to 4.5 W, beyond which the oscillator
became unstable. Injecting the seed laser into a bidirectionally pumped large mode area (LMA) Tm fiber amplifier, a
stable, tunable, narrow linewidth high beam quality amplified signal of >100 W was achieved. In the absence of stable
and sufficiently high power from the seed laser, the amplifier could not be tested to its full potential. The amplifier was
also, converted into an oscillator to investigate its power handling capability. An excellent beam quality and ~200 W of
power were achieved by running the power amplifier as an oscillator. Operation stability of the oscillator was measured
to be more than one hour with a minimum power fluctuation of 0.5%. Currently efforts are underway to increase the seed
laser power to ~10 W, large enough to reduce ASE and mitigate feedback to the master oscillator to demonstrate a 200
W, tunable (150 nm) and narrow linewidth (0.15 nm) MOPA system.
The MOPA system will be one of a number of new state-of-the-art high power lasers to be located at the
Innovative Science & Technology Experimentation Facility, creating a unique laser range facility for next generation
studies and tests across a broad range of sciences and technologies.
Progress is being made developing monolithic, all-fiber 2μm wavelength devices that operate robustly at higher power
levels. This development includes the critical Tm-doped LMA fiber technology, compatible components such as pump
combiners and couplers, along with the optimization of high brightness, high efficiency 790nm pump diodes. In this
paper we present recent CW power scaling results and demonstrate a monolithic MOPA system operating at 400W
output power with around 20% E-O efficiency.
In this paper we present design considerations, thermal and optical modeling results, and device performance for a
ruggedized, compact laser transmitter that utilizes a room temperature quantum cascade (QC) laser source. The QC laser
transmitter is intended for portable mid-infrared spectroscopy applications, where the 3 to 5 μm and 8 to 12 μm
atmospheric transmission window is relatively free of water vapor interference and where the molecular rotational
vibration absorption features can be used to detect and uniquely identify chemical compounds of interest. Initial QC
laser-based sensor development efforts were constrained by the complications of cryogenic operation. However,
improvements in both QC laser designs and fabrication processes have provided room-temperature devices that now
enable significant miniaturization and integration potential for national security, environmental monitoring, atmospheric
science, and industrial safety applications.
The mid-infrared spectral region is of significant interest due to the atmospheric absorption lines present in this region.
We report the development of a compact, highly efficient, high power intra-cavity pumped all-solid-state optical
parametric oscillator (OPO) producing nanosecond pulses with an output tunable from 1.5 microns to 3.4 microns with
pulse energies ranging from 0.5mJ to over 4mJ over the entire range at kHz repetition rates. We have built both watercooled
and air-cooled versions of the OPO for various power level requirements.
In this contribution, we demonstrate that spectral beam combining in an external cavity (EC), a technique which has been
applied previously to shorter wavelength diode laser bars , is also applicable to mid-infrared QC lasers. Within this
concept, the output of multiple emitters from a 4.6 μm emitting QC laser chip is combined in a single, collinear beam.
The average power of an EC-QC laser module realized that way surpasses the output of a corresponding single emitter
by more than a factor of 4. Furthermore, the EC-concept allows a certain degree of wavelength tuning during operation.
The EC, consisting of a collimating lens, a grating and a partially reflecting outcoupling mirror, forces each laser to emit
at a unique wavelength defined by its offset relative to the main optical axis. The EC approach further ensures the
collinear directional and spatial overlap of the individual QC laser output beams forming a single combined output beam.
A simple scheme for efficient generation of mid-IR laser radiation is reported. Using a 50 W thulium fibre laser to pump
a Q-switched Ho:YAG laser 27.3 W of average output power is achieved with an M2 of 1.5 (optical to optical conversion
efficiency 65%) at a wavelength of 2.1 μm. The holmium laser is used to pump a ZGP OPO generating 12.6 W of
average output power in the 3-5 μm waveband (optical to optical conversion efficiency 52%) with a worst case M2 of
2.7. These efficiencies were maintained at 25% and 50% duty cycle operation.
Commercially available quantum cascade gain media has been integrated with advanced coating and die attach
technologies, mid-IR micro-optics and telecom-style assembly and packaging to yield cutting edge performance. When
combined into Daylight's external-cavity quantum cascade laser (ECqcL) platform, multi-Watt output power has been
obtained. Daylight will describe their most recent results obtained from this platform, including high cw power from
compact hermetically sealed packages and narrow spectral linewidth devices. Fiber-coupling and direct amplitude
modulation from such multi-Watt lasers will also be described. In addition, Daylight will present the most recent results
from their compact, portable, battery-operated "thermal laser pointers" that are being used for illumination and aiming
applications. When combined with thermal imaging technology, such devices provide significant benefits in contrast and
The threat posed to aircraft by shoulder-fired missiles has increased to the point where initial testing of laser-based
IRCM systems on commercial aircraft is underway. However, the laser sources used in this testing are complex and
costly. Consequently, the need for a simpler, cost-effective, compact, and power-efficient laser source technology is
urgent. Over the last two years, quantum cascade (QC) lasers have advanced in performance and reliability to the point
where a thorough, experimentally based assessment of the applicability of these lasers as IRCM sources is called for. In
this talk, I will describe Maxion's development of a
wavelength-beam-combined laser source module capable of
emitting, in principle, multi-Watt-levels of optical power in a single, near-diffraction-limited beam. Details of the single
emitter performances in the linear QC laser array are provided as well as the power performance and optical beam
characteristics of the WBC system.
Leveraging Pranalytica's fundamental research into high power and high wallplug efficiency QCL devices and high
performance/reliability QCL packaging technologies, we developed several models of turn-key QCL systems for
security-related applications. Our tabletop high power system produces, at room temperature, more than 2W of
nominally collimated continuous wave radiation at 4.6 μm. Our flashlight-size portable illuminator at 4.6 μm produces
over 100 mW average power portable illuminator at 9.6 μm produces more than 20 mW, both with runtime of ~10 hrs.
These systems are opening the window of QCL acceptance into
real-world security and defense applications. At chip
level, we have demonstrated 3W of CW power at room temperature from a single, high reflectivity coated chip.
Frequency noise reduction of semiconductor lasers using electrical feedback from an optical frequency
discriminator is an efficient and simple approach to realize narrow linewidth lasers. These lasers are of great
interest for applications such as LIDAR, RF photonics and interferometric sensing. In this paper, we review
the technological choices made by TeraXion for the realization of its Narrow Linewidth Laser modules. The
method enables to decrease the linewidth of DFB lasers from several hundreds of kHz to a few kHz. We
present the work in progress to integrate such system into a miniature package and to incorporate advanced
functionalities such as multi-laser phase locking.
In this paper we present the use of high power diode arrays, spectrally stabilised using chirped Volume Bragg Gratings
as a pump source for a Nd:YAG based laser. The temperature dependant performance of a series of different stabilised
diodes, and the side pumped Nd:YAG slab resonator was measured over a 55°C temperature range. The best performing
stabilised LDAs exhibited Q-switched output energy consistent over 80% of the temperature range, and drop off by 40%
at the higher temperature extremes. Beam parameters of the laser such as divergence were found to drop in combination
with input energy. Factors such as spectral drifting of the diodes are also considered and the effect on the resonator is
Compact, efficient visible lasers are important for heads up displays, pointing and illumination, undersea
communications, and less than lethal threat detection. We report on high power red, green, and blue lasers with output
powers above 3 watts and efficiencies greater than 20%, 15%, and 5% respectively.
We report on the progress of highly-reliable, high-efficiency 885-nm diode laser bar arrays. Conduction-cooled hardsoldered
bars rated to 60W and 57% conversion efficiency demonstrate >30,000 device hours under 1-sec on, 1-sec off
hard pulse conditions failure-free. Microchannel-cooled bars rated to 100W and 62% efficiency demonstrate >100,000
accelerated device hours failure-free. Integrated volume Bragg grating fast axis lenses provide wavelength stabilization
at low cost. Vertically stacked arrays (seven bars each) of such configuration are demonstrated with a 0.8 nm FWHM
spectral width and rated to 700W, 53% conversion efficiency.
We report on the development of ultra-high brightness laser diode modules at nLIGHT Photonics. This paper
demonstrates a laser diode module capable of coupling over 100W at 976 nm into a 105 μm, 0.15 NA fiber
with fiber coupling efficiency greater than 85%. The high brightness module has an optical excitation under
0.13 NA, is virtually free of cladding modes, and has been wavelength stabilized with the use of volume
holographic gratings for narrow-band operation. Utilizing nLIGHT's Pearl product architecture, these
modules are based on hard soldered single emitters packaged into a compact and passively-cooled package.
These modules are designed to be compatible with high power 7:1 fused fiber combiners, enabling over
500W power coupled into a 220 μm, 0.22 NA fiber. These modules address the need in the market for high
brightness and wavelength stabilized diode lasers for pumping fiber lasers and solid-state laser systems.
High Power Laser Diode Arrays developed and produced at SCD-SemiConductor Devices support a number of
advanced defence and space programs. High efficiency and unsurpassed reliability at high operating temperatures are
mandatory features for those applications. We report lifetime results of high power bar stacks, operating in QCW mode
that rely on a field-proven design comprising Al-free wafer material technology and hard soldering robust packaging. A
variety of packaging platforms have been implemented and tested at very harsh environmental conditions.
Results include a long operational lifetime study totaling 20 billion pulses monitored in the course of several years for
808 nm QCW bar stacks.. Additionally, we report results of demanding lifetime tests for space qualification performed
on these stacks at different levels of current load in a unique combination with operational temperature cycles in the
range of -10 ÷60 °C.
Novel solutions for highly reliable water cooled devices designed for operation in long pulses at different levels of PRF,
are also discussed. The cooling efficiency of microchannel coolers is preserved while reliability is improved.
InP based diode lasers are required to realize the next generation of eyesafe applications, including direct rangefinding
and HEL weapons systems. We report on the progress of high power eyesafe single spatial and longitudinal mode
1550nm MOPA devices, where we have achieved peak powers in excess of 10W with 50ns pulse widths. A conceptual
model based on our recent MOPA results show the path towards scaling to high powers based on spatial beam
combination with operating conditions suitable for direct rangefinding applications. We also report on the progress
towards high power 14xx and 15xx nm pump lasers for eyesafe HEL systems.
Directional Infrared Countermeasures (DIRCM) is an effective technique to defeat heat-seeking missiles. The major
problem of existing DIRCM is that it may work like a beacon for threats that are not susceptible to the jamming code
implemented: attracting a missile instead of re-directing it away from the aircraft. Ultra-fast laser pulse technology is
discussed as an alternative to a conventional laser DIRCM. An
ultra-fast laser is capable of providing a different type of
countermeasure which is compatible with existing laser based DIRCM pointing systems as it requires much less peak
power than damage inducing systems. A foundation of ultra-fast technology is its unique ability to alter the intrinsic
characteristics of the semiconductor. In this paper, we will only consider the effects of a mild lattice disturbance caused
by relatively low energy ultra-fast (femto-second) and, to some extent, fast (pico-second) laser pulses.
Few cost-effective methods exist for measuring the wave front of
mid- and long-wave infrared beams that span 3-5 and
8-12 μm, respectively. One obvious need within the infrared laser community is the ability to measure the degree of
collimation of an infrared laser beam, e.g. that formed by a beam expanding telescope used with a CO2 laser or a system
of lenses used to collimate a Quantum Cascade Laser (QCL). An ideal approach for this type of metrology is the use of
a lateral shearing interferometer (LSI). An LSI uses various methods to displace ("shear") a beam with respect to itself to
create an interferogram that can subsequently be used for diagnosing the wavefront quality of the beam. Since this type
of interferometer is of the common path variety, it is insensitive to vibration making it ideal for field applications, where
vibration isolation may neither be possible nor practical. In this paper we present and demonstrate, through laboratory
measurements and computer ray tracing simulations, a low-cost LSI using a single commercial off-the-shelf uncoated
ZnSe window in conjunction with an infrared camera. This plane parallel plate LSI configuration was used to
interactively collimate a LWIR beam and also provide quantitative transmitted wavefront error data using static fringe
analysis software. We also present a self-contained review of the theory of lateral shearing interferometry, including the
necessary design equations as applicable to this LSI configuration, to enable researchers to construct a similar beam
diagnostic shearing interferometer from readily available components.
Chalcogenide fibers display a wide transmission window ranging from
2-10.6 μm, ideally suited to the development of
passive and active mid-infrared (MIR) sensors. They are essential building blocks for the integration and miniaturization
of laser-based MIR optical systems for terrestrial, airborne and space-based sensing platforms. Single-mode
chalcogenide fibers have only recently become commercially available and therefore performance data and standard
reproducible processing techniques have not been widely reported. In this paper we present a method for producing high
quality cleaved facets on commercial single-mode As-Se fibers with core and cladding diameters of 28μm and 170μm
respectively. The emitted beam profile from these fibers, using the 9.4μm line of a tunable CO2 laser, showed the
presence of leaky cladding modes due to waveguiding conditions created by the protective acrylate jacket. These
undesirable cladding modes were easily suppressed by applying a gallium coating on the cladding near both input and
output facets. We provide experimental data showing efficient mode suppression and the emission of a circular nearperfect
Gaussian beam profile from the fiber. Furthermore, analyses of the beam, acquired by scanning an HgCdTe
detector, yielded a 1/e2 numerical aperture of 0.11 with a full width half maximum divergence of 11° for these fibers.
The availability of single-mode MIR fibers, in conjunction with recent advances in room temperature quantum cascade
lasers (QCL), could provide compact and light-weight transmitter solutions for several critical defense and nuclear nonproliferation