We report on initial lasing of Tm:Lu2O3 ceramic laser with tunable output in the vicinity of 2 μm. Tm:Lu2O3 ceramic gain materials offer a much lower saturation fluence than the traditionally used Tm:YLF and Tm:YAG materials. The gain element is pumped by 796 nm diodes via a "2-for-1" crossrelaxation energy transfer mechanism, which enables high efficiency. The high thermal conductivity of the Lu2O3 host (~18% higher than YAG) in combination with low quantum defect of ~20% supports operation at high-average power. Konoshima’s ceramic fabrication process overcomes the scalability limits of single crystal sesquioxides. Tm:Lu2O3 offers wide-bandwidth amplification of ultrashort pulses in a chirped-pulse amplification (CPA) system. A laser oscillator was continuously tuned over a 230 nm range from 1890 to 2120 nm while delivering up to 43W QCW output with up to 37% efficiency. This device is intended for initial testing and later seeding of a multi-pass edge-pumped disk amplifier now being developed by Aqwest which uses composite Tm:Lu2O3 disk gain elements.
We report on testing of an edge-pumped ceramic Yb:YAG disk laser having a tailored spatial gain profile for preferential amplification of the TEM00 mode. The disk has a composite construction with a Yb-doped large-aperture central portion cosintered with an undoped perimetral edge. Light from multi-kW diodes is transported though the disk edge and absorbed in the Yb-doped center. This configuration makes it poss¬ible to conveniently arrange the diode light and produce a spatially flat gain profile, such as is desir¬able for the amplification of a spatial flat top beam or a tailored gain profile . Amplified spontan¬eous emis¬sion (ASE) and parasitic lasing is mitigated by the geometry of the laser disk edge, which is designed to efficiently outcouple laser fluorescence .
This work experimentally investigated the tailored spatial gain profile and the lasing performance of TEM00 mode (Gaussian spatial profile) beam without the distorting effects of gain saturation. Compari¬son of the lasing performance of a flat spatial gain to that with tailored gain is presented. This work was supported in-part by the US Department of Energy grants DE-SC0013762 and DE-SC0015834.
1. Drew A. Copeland and John Vetrovec, “Gain Tailoring Model and Improved Optical Extraction
in CW Edge–Pumped Disk Amplifiers,” SPIE Vol. 8235, 82350U (2012).
2. John Vetrovec, Drew A. Copeland, Amardeep S. Litt, Suraj J. Thiagarajan, and Eldridge Briscoe "Stored Energy and Gain in an Edge-Pumped Ceramic Yb:YAG Disk Laser under Intense Pumping," SPIE Vol. 10084, 1008407 (2017).
We report on testing of an edge-pumped ceramic Yb:YAG disk laser for pulse amplification under intense pumping. The disk has a composite construction with Yb-doped central portion cosintered with an undoped perimetral edge. Light from multi-kW pulsed diodes is transported though the disk edge and absorbed in the Yb-doped center. This configuration results in a very simple and compact laser gain module. The disk is operated as a storage amplifier. Amplified spontaneous emission and parasitic lasing is alleviated by the geometry of the laser disk edge rather than absorption cladding. Our test results indicate that this approach offers a robust mitigation of ASE. This work presents results of stored energy, gain, and ASE mitigation in the Yb:YAG disk laser under intense pumping.
Tm:Lu2O3 has a multi–featured absorption spectrum in the usual pump band around 796 nm with peaks and valleys narrower than the bandwidth of conventional pump diodes in this range. As a result, accurate prediction of the spatial deposition of absorbed pump power is rather challenging. This is of particular importance for the edge-pumped disk laser where the spatial gain profile is adjusted by temperature tuning of the laser pump diodes to optimize performance for amplification of pulses with spatial top hat or with spatial Gaussian profiles. The frequently used "lumped-line" pump model was found inadequate for Tm:Lu2O3. This work reports on the development of a spectral absorption model for a more accurate prediction of pump power deposition and its correlation with the gain uniformity and amplifier output pulse energy.
We report on a Yb:YAG laser amplifier for ultrashort pulse applications at kW-class average power. The laser uses two large-aperture, disk-type gain elements fabricated from composite ceramic YAG material, and a multi-pass extraction architecture to obtain high gain in a chirped-pulse amplification system. The disks are edge-pumped, thus allowing for reduced doping of the host material with laser ions, which translates to lower lasing threshold and lower heat dissipation in the Yb:YAG material. The latter makes it possible to amplify a near diffraction-limited seed without significant thermo-optical distortions. This work presents results of testing the laser amplifier with relay optics and passive polarization switching configured for energy extraction with up to 40 passes through the disks. Applications for the ultrashort pulse laser amplifier include producing a laser-induced plasma channel, laser material ablation, and laser acceleration of atomic particles.
We report on the investigation of a novel ceramic Tm:Lu2O3 amplifier lasing at around 2-μm and offering efficient generation of high-energy pulses with high-peak power at high repletion rate, high efficiency, and with near-diffraction-limited beam quality (BQ). The amplifier has a bandwidth of over 300 nm, which offers broad tunability. The bandwidth also supports generation of ultrashort pulses in the femtosecond regime. The “2-for-1” pump architecture of the Tm ion enables high optical-to-optical efficiency while pumping at around 800 nm. High thermal conductivity of the Lu2O3 host supports operation at high-average power. The ceramic nature of the Lu2O3 host overcomes the scalability limits of single crystal sesquioxides.
We report on an investigation of novel 2 μm thulium (Tm)-based laser accelerator driver (LAD) offering efficient generation of high-energy pulses with high-peak power at high pulse repetition rate (PRF), high efficiency, and with near-diffraction-limited beam quality (BQ). Laser acceleration of electrons by ultrashortpulse laser-generated plasmas offers accelerators of much reduced size and cost compared to conventional accelerators of the same energy, thus replacing the traditional mammoth-size and costly accelerator research facilities with room-size systems1. A LAD operating at 2 μm wavelength offers ponderomotive forces four times that of 1 μm wavelength and six times that of a traditional 0.8 μm wavelength LAD. In addition, the Tm bandwidth of nearly 400 nm offers > 15% tunability and generation of ultrashort pulses down to <30 fs. The “2-for- 1” pump quantum efficiency of the Tm ion enables > 20% wall-plug efficiency. This work presents a preliminary analysis of Tm-based LAD configurations.
We report on a Yb:YAG laser amplifier for ultrashort pulse applications at kW-class average power. The laser uses two large-aperture, disk-type gain elements fabricated from composite ceramic YAG material, and a multi-pass extraction architecture to obtain high gain in a chirped-pulse amplification system. The disks are edge-pumped, thus allowing for reduced doping of host material with laser ions, which translates to lower lasing threshold and lower heat dissipation in the Yb:YAG material. The latter makes it possible to amplify a near diffraction-limited seed without significant thermo-optical distortions. This work presents results of testing the laser amplifier with relay optics configured for energy extraction with up to 40 passes through the disks. Applications for the ultrashort pulse laser amplifier include producing laser-induced plasma channel, laser material ablation, and laser acceleration of atomic particles.
We report on a new class of laser amplifiers for inertial confinement fusion (ICF) drivers based on a Yb:YAG ceramic disk in an edge-pumped configuration and cooled by a high-velocity gas flow. The Yb lasant offers very high efficiency and low waste heat. The ceramic host material has a thermal conductivity nearly 15-times higher than the traditionally used glass and it is producible in sizes suitable for a typical 10- to 20-kJ driver beam line. The combination of high lasant efficiency, low waste heat, edge-pumping, and excellent thermal conductivity of the host, enable operation at 10 to 20 Hz at over 20% wall plug efficiency while being comparably smaller and less costly than recently considered face-pumped alternative drivers using Nd:glass, Yb:S-FAP, and cryogenic Yb:YAG. Scalability of the laser driver over a broad range of sizes is presented.
We report on initial testing of an edge-pumped erbium-based disk laser operating at 1.53 micron. The laser uses a single laser disk having a composite glass construction with erbium-ytterbium co-doped center and undoped perimetral edge designed to channel pump light. Erbium is pumped to a laser transition by 940-nm diode radiation, which is first absorbed by ytterbium with subsequent energy transfer to erbium. This work presents results of initial testing of the laser with resonator optics configured for power extraction with two passes through the disk.
We report on the development of a novel, ultra-low thermal resistance active heat sink (AHS) for thermal management of high-power laser diodes (HPLD) and other electronic and photonic components. AHS uses a liquid metal coolant flowing at high speed in a miniature closed and sealed loop. The liquid metal coolant receives waste heat from an HPLD at high flux and transfers it at much reduced flux to environment, primary coolant fluid, heat pipe, or structure. Liquid metal flow is maintained electromagnetically without any moving parts. Velocity of liquid metal flow can be controlled electronically, thus allowing for temperature control of HPLD wavelength. This feature also enables operation at a stable wavelength over a broad range of ambient conditions. Results from testing an HPLD cooled by AHS are presented.
We report on initial testing of an edge-pumped Yb:YAG disk laser having a composite ceramic construction
with undoped perimetral edge. The edge is designed to channel pump light while efficiently outcoupling
amplified spontaneous emission (ASE). Edge-pumping allows for reduced doping of crystals with
laser ions, which translates to a lower lasing threshold in Yb:YAG material and much reduced waste heat
flux. Uniform gain and stable lasing were achieved.
We report on initial testing of an edge-pumped Yb:YAG disk laser. The assembled laser uses two laser
disks having a composite ceramic construction with undoped perimetral edge designed to channel pump
light while efficiently outcoupling amplified spontaneous emission (ASE). Edge-pumping allows for
reduced doping of crystals with laser ions, which translates to a lower lasing threshold in Yb:YAG
material and much reduced waste heat flux. This work presents results of initial testing of the laser with
one Yb:YAG laser disk and resonator optics configured for power extraction with two passes through the
The effect of gain tailoring upon the optical extraction and OPD in a CW edge-pumped disk amplifier is examined using
a two-dimensional model of diode pumping coupled with a two-dimensional, geometric model of optical extraction by a
Gaussian profile beam from a Yb:YAG medium1. The gain medium is described by the well-known quasi-three level
model of Beach2,3. Gain tailoring is accomplished by focusing the diode pump beam using cylindrical lenses. The diode
pump beam, optical extraction, and gain medium models are described after which the pump absorption efficiency, energy
deposition uniformity, output energy, and maximum peak-to-valley (PV) OPD are examined as a function of the
pump lens focal length and output aperture radius as well as amplifier input seed energy, number of roundtrip amplifier
passes, and diode pump power. It is shown that using pump beam focusing to tailor the gain radially deposits more energy
in the central region of the disk and thus results in improved optical extraction because a Gaussian input optical
beam preferentially accesses the central region of the disk. With gain tailoring one can achieve the same amplifier output
energies as without gain tailoring but using less pump power and/or amplifier seed energy, resulting in reduced disk
heating and diode-pump waste heat. Although the maximum PV OPD is larger, the central region of the thermally-induced
OPD remains relatively uniform, allowing one to increase the output energy with only modest increases in the effective
We report on the development of a novel active heat sink for high-power laser diodes offering unparalleled
capacity in high-heat flux handling and temperature control. The heat sink employs convective heat transfer
by a liquid metal flowing at high speed inside a miniature sealed flow loop. Liquid metal flow in the loop is
maintained electromagnetically without any moving parts. Thermal conductance of the heat sink is
electronically adjustable, allowing for precise control of diode temperature and the laser light wavelength.
This paper presents the principles and challenges of liquid metal cooling, and data from testing at high heat
flux and high heat loads.
We report on the development of a novel 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 output light wavelength. When pumping solid-state lasers, diode wavelength can be precisely
tuned to the absorption features of the laser gain medium. This paper presents the AHS concept, scaling
laws, model predictions, and data from initial testing.
We report on the development of a ytterbium-based disk amplifier for an ultra-short pulse laser using
edge-pumped architecture and offering excellent scalability to high-average power in the kW-range. The
disk has a composite construction with undoped perimetral edge designed to channel pump light while
efficiently outcoupling amplified spontaneous emission. Uniform extraction of waste heat together with
uniform pumping offers very low optical path distortion and allows for amplification of near diffraction
limited beams in nanosecond-class pulses. This work discusses performance modeling of the edgepumped
disk amplifier using a newly developed time-dependent 2-dimensional (spatial) model for
dynamic pumping and extraction. Selection of laser materials and an innovative two-disk amplifier
architecture for multiple extractions are also presented.
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.
We report on a novel heat sink for high-power laser diodes offering unparalleled capacity in high-heat flux
handling and temperature control. The heat sink uses a liquid coolant flowing at high speed in a miniature closed
and sealed loop. Diode waste heat is received at high flux and transferred to environment, coolant fluid, heat pipe,
or structure at a reduced flux. When pumping solid-state or alkali vapor lasers, diode wavelength can be
electronically tuned to the absorption features of the laser gain medium. This paper presents the heat sink
physics, engineering design, performance modeling, and configurations.
We report on a novel high-performance active heat sink (AHS) offering unparalleled capacity in high-heat flux
handling, heat spreading, and temperature control. AHS couples directly to standard high-brightness light
emitting diodes (LED) packages. It efficiently removes high-flux waste heat from the LED slug and transfers it to
ambient air. AHS has variable thermal conductance that can be electronically adjusted to compensate for changes
in ambient temperatures or to adjust the light color. This paper presents AHS physics, engineering design, and
results from numerical simulations. Applications to screw-in replacements for the R30 lamp are discussed.
We report a novel coolant recirculation loop for high-power laser diodes which allows operating diode bar heat exchangers at their design coolant Reynolds number while consuming as little as 20% of their nominal coolant supply inflow. While operating in a single-phase regime, the new concept uses low coolant flow-rates comparable to proposed evaporative coolers. Unlike evaporative coolers, the new concept is compatible with many standard microchannel or impingement-type heat exchanger designs. The theory, design, and applications are presented.
We report on a novel resonantly-pumped, erbium (Er)-based, gas-cooled disk laser (GCDL) scalable to highaverage
power (HAP). The GCDL uses edge-pumped composite laser disks known for their near perfect
pump uniformity and compact configuration. Edge pumping enables a long path for pump absorption, which
permits using low Er concentration and limits upconversion losses. Resonant operation reduces the waste
heat load and enables the use of gas rather than liquid for disk cooling. These attributes make it possible to
engineer a lightweight and compact laser device operating at eye-safer wavelengths. This paper presents a
GCDL concept design and evaluates its performance for several host materials and operating conditions.
This work describes recent progress in the development of a solid-state disk laser that uses composite laser disks in active mirror configuration, edge-pumping, and cooling by microchannel-type heat exchanger. An innovative pressure clamping technique was used to mitigate thermo-mechanical distortions in the disk. A test article
Yb:glass disk was operated at a thermal load corresponding to about 1 kW laser output in a steady-state regime with surface temperatures around 90°C while exhibiting less than λLaser/10 rms phase error. Measured pump uniformity approaching 90% validated the edge-pumping architecture.
This work presents a comparative study of gain media for diode-pumped, high-average power solid-state disk lasers. Relative performance of Nd and Yb doped into several host media is evaluated under several pump and lasing conditions.
This work describes recent progress in the development of solid-state laser using a composite disk the active mirror configuration. Pump diode arrays are placed around the perimeter of the disk and pump light is injected into the undoped edge. Uniform laser gain can be achieved with proper choice of lasant doping level, diode placement, and diode divergence. Effective reduction of thermo-optical distortions makes this laser suitable for pulse amplification at high-average power.
High-average power solid-state lasers use Nd or Yb lasants doped into a variety of host materials. Desirable properties for such materials include favorable spectroscopy, thermomechanical and thermo-optical parameters, and availability of the host material in large size and good quality. A laser designer often faces difficult choices because no combination of dopant and host materials incorporates all of the most desirable properties. This work presents a comparative study of gain media for diode-pumped, high-average power solid-state disk lasers. Relative performance of Nd and Yb doped into several host media is evaluated under several pump conditions.
This work presents an improved disk laser concept, where a diode- pumped disk is hydrostatically clamped to a rigid substrate and continuously cooled by a microchannel heat exchanger. Effective reduction of thermo-optical distortions makes this laser suitable for continuous operation at ultrahigh-average power.
This paper describes a high-energy laser (HEL) concept based on a disk-type solid-state laser operating in active mirror mode. The gain medium disks have high-performance real-time cooling that allows the laser to operate continuously. This configuration of the laser shows excellent scalability to high-average power required for directed energy applications and can be integrated into a simple, compact, lightweight, and affordable unit. The paper also discusses engineering concepts for integrated HEL, power-size-weight scaling model, as well as options for prime power and thermal management.
This work presents concept and scaling considerations for a solid-state laser with a gain medium disk operating in the active mirror mode. The disk is of composite construction formed by bonding undoped optical medium to the peripheral edges of a gain medium disk. Pump diode arrays are placed around the perimeter of the composite disk and pump light is injected into the undoped edge. With proper choice of lasant doping, diode placement and diode divergence, a uniform laser gain can be achieved across large portions of the disk. To mitigate thermal deformations, the gain medium disk is pressure-clamped to a rigid, cooled substrate. Effective reduction of thermo-optical distortions makes this laser suitable for operation at high-average power.
This work presents a concept and scaling considerations for a diode-pumped solid-state laser operating in the active mirror mode. The laser uses relatively thin gain medium with large aperture that is pressured-clamped onto a transparent substrate with an internal microchannel type heat exchanger. Pump radiation is injected through the transparent substrate into the back face of the gain medium. Effective reduction of transverse temperature gradients makes this laser suitable for operation at high-average power while delivering good beam quality.
The Chemical Oxygen-Iodine Laser (COIL) has been studied for several industrial applications. Recent demonstrations have shown that lasers can be highly effective for size-reduction cutting of radioactivelycontaminated structures.
This work describes a conceptual design of a chemical oxygen-iodine laser (COIL) where diluent gas is continuously recirculated in a closed cycle. Scaling laws, component design, and expected performance are discussed.
This work examines the prospects of generating gas-phase O2(1Æ) from thermal decomposition of (C6H5O)3PO3 for use in the oxygen-iodine laser. The process promises major advantages over the traditional production of O2(1Æ) from the reaction of C12 with basic hydrogen peroxide, namely (1) producing O2(1Æ) from a single liquid fuel (as opposed to reacting liquid fuel and oxidant gas), (2) fuel with a long storage life, (3) up to four times lower heat release which greatly reduces needs for refrigeration, and (4) simple hardware.
In a chemical oxygen-iodine laser (COIL), chemically prepared, gaseous gain medium at 3-10 Torr pressure is drawn through the laser cavity by vacuum suction. Multiple-stage vacuum pumps such as Roots blowers or steam ejectors are typically used to receive and compress the gas flowing from the laser and exhaust it to the atmosphere. The size and weight of such vacuum pumps present a significant challenge to engineering and packaging a transportable COIL system.
The dismantlement of obsolete nuclear facilities is a major challenge for both the US Department of Energy and nuclear power utilities. Recent demonstrations have shown that lasers can be highly effective for size reduction cutting, especially for the efficient storage and recycling of materials. However, the full benefits of lasers can only be realized with high average power beams that can be conveniently delivered, via fiber optics, to remote and/or confined areas. Industrial lasers that can meet these requirements are not available now or for the foreseeable future. However, a military weapon laser, a Chemical Oxygen Iodine Laser (COIL), which has been demonstrated at over a hundred kilo Watts, could be adapted to meet these needs and enable entirely new industrial applications. An 'industrialized' COIL would enable rapid sectioning of thick and complex structures, such as glove boxes, reactor vessels, and steam generators, accelerating dismantlement schedules and reducing worker hazards. The full advantages of lasers in dismantlement could finally be realized with a portable COIL which is integrated with sophisticated robotics. It could be built and deployed in less than two years, breaking the paradigm of labor-intensive dismantlement operations and cutting processing times and costs dramatically.
The chemical oxygen-iodine laser (COIL) uses a reaction of gaseous chorine and aqueous solution of basic oxygen peroxide (BHP) to produce oxygen singlet delta molecules, O2(1(Delta) ). Quenching of O2(1(Delta) ) during its extraction from the BHP solution and quenching of excited atomic iodine I* by water vapor from the O2(1(Delta) ) production process are well-known parasitic effects in COIL. This paper shows that both of these effects can be significantly reduced by replacing the hydrogen 1H1 isotope atoms in BHP by the 1H2 isotope atoms. In addition to restoring laser power lost to parasitic quenching, use of basic deuterium peroxide (BDP) rather than BHP is expected to allow generation of O2(1(Delta) ) at elevated temperature. This approach promises to save refrigerant, reduce the risk of BDP freezing, and delay precipitation of salt form BDP solution. Methods for producing BDP are outlined.
This work describes a conceptual design of an industrial chemical oxygen-iodine laser and its applications to dismantlement of nuclear reactors and to aluminum cutting and welding. Choices of specific technologies and system components are made with the aid of a system cost model.
This work describes a configuration of an electrochemical apparatus for production chlorine and basic hydrogen peroxide and discusses its use in a continuously operating COIL system consuming only electric power and air.
Over the last several years, Rocketdyne has conducted a number of experiments on advanced jet generators. Both cross flow jet generator and counter flow jet generators have been tested. We have made laser power measurements at our Continuous Wave Chemical Laser Facility (CWLL) and at the Air Force Phillips Laboratory RADICL test facility. A test there resulted in a measured chemical efficiency of 29.6%. This is the highest efficiency reported for a supersonic oxygen-iodine chemical laser.
The chemical oxygen-iodine laser derives its energy from the reaction of basic hydrogen peroxide with chlorine. The traditional oxygen-iodine laser uses an 'open loop' cycle, in which fresh reactants are furnished in bulk form. This approach is not suitable for a continuously operating laser because supplying fresh reactants and disposing of reaction products are expensive and require significant logistics. This work describes a new concept for continuous in-situ regeneration of chlorine and basic hydrogen peroxide.
This paper discusses the use of high-power lasers to remotely process material for decommissioning and dismantlement of nuclear facilities. Process requirements are established and suitable laser systems are compared. The chemical oxygen- iodine laser was identified as the leading candidate for long term dismantlement activities because it offers a high-power, high-brightness beam that can be remotely delivered into radiation containment by optical fibers.
This work evaluates the prospects of developing a chemical oxygen-iodine laser which could be used for cutting, welding, and other material processing applications that can benefit from a high-power, high-brightness, fiber-delivered laser beam. It shows how application-specific requirements drive the technological and economic considerations of the iodine laser.