Disk Laser System Research Articles

Diode pumped solid state kilohertz disk laser system for time-resolved combustion diagnostics under microgravity at the drop tower Bremen

We describe a specially designed diode pumped solid state laser system based on the disk laser architecture for combustion diagnostics under microgravity (μg) conditions at the drop tower in Bremen. The two-stage oscillator-amplifier-system provides an excellent beam profile (TEM00) at narrowband operation (Δλ < 1 pm) and is tunable from 1018 nm to 1052 nm. The laser repetition rate of up to 4 kHz at pulse durations of 10 ns enables the tracking of processes on a millisecond time scale. Depending on the specific issue it is possible to convert the output radiation up to the fourth harmonic around 257 nm. The very compact laser system is integrated in a slightly modified drop capsule and withstands decelerations of up to 50 g (>11 ms). At first the concept of the two-stage disk laser is briefly explained, followed by a detailed description of the disk laser adaption to the drop tower requirements with special focus on the intended use under μg conditions. In order to demonstrate the capabilities of the capsule laser as a tool for μg combustion diagnostics, we finally present an investigation of the precursor-reactions before the droplet ignition using 2D imaging of the Laser Induced Fluorescence of formaldehyde.

Yb:YAG ceramics application for high energy cryogenic disk amplifier development

AbstractUsing two 20 mm in diameter, 1.4 mm thick, 5 at% doping Yb:YAG ceramic active elements (AEs) we reached 233 mJ at 143 Hz in the output with 70 ns, 30 mJ input pulses. According to our 3D calculations we extracted about half of the stored energy. To our knowledge, this output result is the best among all high repetition rate cryogenic pulse Yb:YAG ceramic thin disk laser systems.

The quasi-cavity performance in a back-reflection regenerative pumping system for high power disk laser systems

A quasi-cavity equipped on both sides with mirrors that have a transparent hole at their centers is used for a back-reflection regenerative pumping system for a thin-disk solid state laser instead of the multipass pumping system. We have investigated thermo-optical and thermo-mechanical properties of the quasi-cavity by employing finite element analysis (FEA) numerical method in a cylindrical and a rectangular quasi-cavity. Temperature, displacement distribution and variation of refractive index of the rectangular quasi-cavity in different pump powers have been calculated for several materials. We recommend a combination of diamond/YAG crystal in making quasi-cavity for better performance in high power quasi-end-pumped thin disk laser.

Extending the narrow-bandwidth tunability of a thin disk Yb:YAG laser regenerative amplifier

We investigate the characteristics of a thin disk laser system based on the master oscillator-power amplifier design. The amplifier emits parasitic laser oscillation (PL) when the wavelength of the tunable narrow-bandwidth seed pulse is detuned more than 4 nm from the gain maximum at 1030 nm. For suppression of this unwanted PL, a birefringent filter (Lyot filter) was inserted into the amplifier cavity in order to generate wavelength selective losses, especially at the gain maximum of the Yb:YAG crystal. It is shown that the tunability range of the laser system can be extended by a factor of 4, when a properly chosen Lyot filter is applied and its angle of rotation is adapted to the seed wavelength of the system.

Flame turbulences recorded at 1 kHz using planar laser induced fluorescence upon hot band excitation of OH radicals

Laser-induced fluorescence (LIF) in flames is excited by a diode-pumped all-solid-state disk laser system which operates at a pulse repetition rate of 1 kHz and a tunable wavelength around 1030 nm. The laser fundamental is converted to 343 nm and used to excite into the hot band transition $A^2\Sigma^{+}(v^{\prime}=0)\gets{X}^{2}{\Pi}(v^{\prime\prime}=1)$ of OH radicals in H2/O2 diffusion flames of an industrial burner and in the premixed flame of a microburner. The OH radical emission around 308 nm is resolved spectrally and spatially using a light-sheet technique. Imaging of the planar LIF (PLIF) by a gated camera visualizes the turbulent flame behavior on the millisecond time scale without averaging. To our knowledge this is the first time that an all-solid-state laser providing at the same time a kHz repetition rate as well as pulse energies of up to 5.5 mJ is available for PLIF observation of OH radicals.

All-optical bistability in nematic liquid crystals at 20 μW power levels

Optical switches at power levels as low as 14 μW, allowing bistable operation with compact disk laser systems, are reported in optimized cavities containing planar-aligned nematic liquid crystals.

Intensity variation of reflected energy from spherical glass shell laser fusion targets

The fraction of the energy reflected by spherical glass shell targets irradiated with 1.06-μm laser pulses is measured for average intensities up to 4×1015 W/cm2. The on-target energies ranged up to 230 J with laser pulse half-widths of from 0.03 to 1.0 nsec. The glass shells ranged in diameter from 57 to 553 μm. Using the KMS Fusion two-channel disk laser system, the shells were illuminated at 1.06 μm from opposite sides at near-normal incidence. Two illumination systems were investigated. In the first, the target was illuminated with a pair of f/0.6 lenses providing approximately 80° per side (full cone angle) of near-normal incidence. In the second, the f/0.6 lenses were used in conjunction with an ellipsoidal mirror system which provides 144° per side (full cone angle) of normal illumination to with 18°. The fraction of the energy reflected from the targets was found to vary as a power of the average intensity on target over the range 4×1013 to 4×1015 W/cm2. Within this range no sudden onset of enhanced energy absorption or reflection by the targets was observed. Measurements were also made of the 1.06-μm radiation scattered from the target at 45° and 90° to the laser axis. The scattering was roughly isotropic. The light reflected from the targets was found to be approximately 20% depolarized.

Superfluorescence Limitations on the Inversion Process in Large-Aperture Laser Amplifiers

A Monte Carlo computation procedure has been used to study the effect of superfluorescence losses upon the design of a large-aperture disk laser system in terms of the enhanced photon flux density. This parameter is indicative of the maximum attainable population inversion. It was found that laser disks up to 6 in. in diam are capable of useful optical energy storage. The technique can also be applied to other laser geometries to estimate superfluorescence effects more readily than previous numerical integration methods.

A large-aperture disk laser system

A large-aperture disk laser system