Brian J. Comaskey

Modular microchannel cooled heatsinks for high average power laser diode arrays

Detailed performance results for an efficient and low thermal impedance laser diode array heatsink are presented. High duty factor or CW operation of fully filled laser diode arrays is made possible at high average power. Low thermal impedance is achieved using a liquid coolant and laminar flow through microchannels. The microchannels are fabricated in silicon using an anisotropic chemical etching process. A modular rack-and-stack architecture is adopted for the heatsink design, allowing arbitrarily large two-dimensional arrays to be fabricated and easily maintained. The excellent thermal control of the microchannel cooled heatsinks is ideally suited to pump array requirements for high average power crystalline lasers. >

Optical parametric chirped-pulse amplifier as an alternative to Ti:sapphire regenerative amplifiers

We demonstrated a high-pulse energy, femtosecond-pulse source based on optical parametric chirped-pulse amplification. We successfully amplified 1-microm broadband oscillator pulses to 31 mJ and recompressed them to 310-fs pulse duration, at a 10-Hz repetition rate. The gain in our system is 6 x 10(7), achieved by the single passing of only 40 mm of gain material pumped by a commercial Q-switched Nd:YAG laser. This relatively simple system replaces a more complex Ti:sapphire regenerative-amplifier-based chirped-pulse amplification system. Numerous features in design and performance of optical parametric chirped-pulse amplifiers make them a preferred alternative to regenerative amplifiers based on Ti:sapphire in the front end of high-peak-power lasers.

High average powers diode pumped slab laser

The authors have developed and tested stackable microchannel cooled laser bar diode pump packages suitable for direct pumping of slab lasers at high duty factor. A stack of 41 diode packages gives a pump array of 13.5 cm/sup 2/ and produces a peak power of 4000 W and an average power of 1000 W for an average irradiance of 75 W/cm/sup 2/. A high average power, total internal reflection face pumped Nd:YAG laser using 80 diode packages has been constructed. Preliminary testing of the slab laser using a 20% subset of diode packages arranged to pump a 4 mm*4 mm*80 mm volume of the slab has been completed. Seventy watts average power is obtained at 2.5 kHz pulse repetition rates and 100 mu s pulse widths. >

Characterization of the heat loading of Nd-doped YAG, YOS, YLF, and GGG excited at diode pumping wavelengths

The parameter /spl xi/ (xi) is proposed as an alternative to the traditional solid-state laser media heating parameter, /spl chi/ (chi). /spl xi/ is the ratio of heat produced to energy absorbed, and /spl chi/ is the ratio of heat produced to the maximum stored energy in the upper laser level. The parameter /spl xi/ is particularly relevant to diode pumped systems. We demonstrate an experimental /spl xi/ characterization based on the determination of the steady state cooling rate (hence heating rate) of small sample crystals subjected to pump laser heating. Using measured fluorescent lifetimes of the samples and near zero doping (intrinsic) values, the doping independent (zero doping or zero quenching) parameters /spl chi//spl phi/ and /spl xi//spl phi/ are determined. The results for all samples are in excellent agreement with calculations based solely on energy defect and nonradiative quenching of the upper level. >

Angular effects and beam quality in optical parametric amplification

Advances in optical parametric devices, in particular those requiring high conversion efficiency, rely on pump laser and gain medium properties. We describe and theoretically model the source of dephasing due to angular deviation from ideal phase matching in optical parametric amplification. Real laser beams have angular content, which is described by their spatial frequency spectrum. Such beams cannot be treated as single plane waves in nonlinear interactions. Our mathematical model is based on a plane wave decomposition of Gaussian and top-hat beams into their components in spatial frequencies. Several popular nonlinear materials (beta-barium borate, lithium borate, and potassium dihydrogen phosphate) are examined for phase matching angles and dephasing is rigorously calculated. The impact of the beam angular content on small signal gain and on conversion efficiency in the strongly depleted regime is evaluated numerically. In addition, a criterion is formulated for beam quality tolerance in optical parametric amplifiers, for critical and noncritical phase matching. The impact of initial conditions in optical parametric amplification is considered. Our calculations are intended primarily for devices pumped with long (nanosecond) pulses.

Microchannel heatsinks for high average power laser diode arrays

Detailed performance results and fabrication techniques for an efficient and low thermal impedance laser diode array heatsink are presented. High duty factor or even CW operation of fully filled laser diode arrays is enabled at high average power. Low thermal impedance is achieved using a liquid coolant and laminar flow through microchannels. The microchannels are fabricated in silicon using a photolithographic pattern definition procedure followed by anisotropic chemical etching. A modular rack-and-stack architecture is adopted for the heatsink design allowing arbitrarily large two-dimensional arrays to be fabricated and easily maintained. The excellent thermal control of the microchannel cooled heatsinks is ideally suited to pump array requirements for high average power crystalline lasers because of the stringent temperature demands that result from coupling the diode light to several nanometers wide absorption features characteristic of lasing ions in crystals.

High‐reliability silicon microchannel submount for high average power laser diode arrays

A simple and highly reliable package consisting of a 1‐cm‐long AlGaAs laser diode array mounted directly on a silicon microchannel cooler has been demonstrated. 3.4×109 shots were logged on this device at an average optical output of 8.75 W with only a 6% increase in current required to hold the light output constant. This extrapolates to a current doubling lifetime of 1.6×1011 shots. The thermal impedance was also measured to be 0.014 °C/(W/cm2).

The ionization potential of neutral iron, Fe i, by multistep laser spectroscopy

Three-step laser excitation was used to populate and observe members of Rydberg series in neutral iron with high effective quantum numbers. These series converge to the ground and to the first excited state of singly ionized iron. The photoionization threshold was also observed. Analyses of the Rydberg series yield the value 63 737(1) cm−1 or 7.9024(1) eV as the ionization potential of neutral iron.

24-W average power at 0.537 μm from an externally frequency-doubled Q-switched diode-pumped Nd:YOS laser oscillator

A diode-pumped single Nd:YOS rod laser is operated at 110 Hz with 830-mJ free-lase pulses and 380-mJ, 13-ns (FWHM) Q-switched pulses. External doubling with an 8-mm-long KTP crystal results in 24 W at 0.537 µm after thermalization.

One-kilowatt average-power diode-pumped Nd:YAG folded zigzag slab laser

High average power Nd:YAG lasers are increasingly interesting for industrial applications such as drilling and machining. Diode pumping of this solid state medium offers longer services intervals, reduced thermal optical distortions, higher system efficiency and more compact packaging than lamp pumping. The zigzag slab geometry is well suited for applications where the average power exceeds a few hundred watts and a good beam quality is desired, particularly if the laser pumping level is to be varied. We present the status of our latest upgrade to our (originally 300 watt1) diode pumped slab laser. In what follows we first describe the diode pump source. We then discuss the zigzag slab laser design and its present performance.