Gunnar Arisholm

Midinfrared laser source with high power and beam quality

A simple scheme for generation of high power in the midinfrared is demonstrated. By using a 15 W thulium-doped fiber laser emitting at 1907 nm to pump a Q-switched Ho:YAG laser, we obtained 9.8 W at 2096 nm at a 20 kHz pulse repetition rate with excellent beam quality. The output of this laser was used to pump a doubly resonant zinc germanium phosphide based optical parametric oscillator, and we obtained 5.1 W average power in the 3-5 microm range with M2 approximately = 1.8.

Powerful red-green-blue laser source pumped with a mode-locked thin disk laser

We present a red-green-blue laser source with average powers of 8 W in the red, 23 W in the green, and 10.1 W in the blue. The entire pump power for the nonlinear conversion stages is provided by a single laser oscillator without any amplifier stages. Our system does not require any synchronized cavities, and all nonlinear crystals except one are critically phase matched at room temperature.

Measurement of the nonlinear coefficient of orientation-patterned GaAs and demonstration of highly efficient second-harmonic generation

Quasi-phase-matched (QPM) GaAs structures, 0.5 mm thick, 10 mm long, and with 61-mum grating periods, were grown by a combination of molecular-beam epitaxy and hydride vapor phase epitaxy. These were characterized by use of mid-IR second-harmonic generation (SHG) with a ZnGeP(2) (ZGP) optical parametric oscillator as a pump source. The SHG efficiencies of QPM GaAs and QPM LiNbO(3) were directly compared, and a ratio of nonlinear coefficients d(14)(GaAs)/d(33) (LiNbO(3))=5.01+/-0.3 was found at 4.1-mum fundamental wavelength. For input pulse energies as low as 50muJ and approximately 60-ns pulse duration, an internal SHG conversion efficiency of 33% was measured in QPM GaAs.

General numerical methods for simulating second-order nonlinear interactions in birefringent media

Two computational methods are common for simulating the evolution of three beams propagating in a birefringent medium and interacting through a second-order nonlinearity: the split-step method and solution of the coupled equations for the amplitudes of the spatial frequency components of the beams (Fourier-space method). I (i) compare the accuracy and computational cost of both methods, (ii) investigate the effect of using a first-order expansion for the refractive index as a function of propagation direction, and (iii) generalize both methods to handle arbitrary propagation directions in biaxial crystals. It turns out that the Fourier-space method with a Runge–Kutta solver gives best accuracy, but a symmetrized split-step method may be faster when low accuracy is sufficient. The first-order expansion for the refractive index gives a very small error for well-collimated beams, but the approximation is not important for computational efficiency. Modeling of parametric amplification outside the principal planes of a biaxial crystal is demonstrated, and to the authors knowledge this process has not been modeled in such detail before.

A 22-watt mid-infrared optical parametric oscillator with V-shaped 3-mirror ring resonator

We report on a ZnGeP(2)-based optical parametric oscillator (OPO) with 22 W of output power in the 3-5 µm range and a beam quality factor M(2) ≈1.4. The OPO uses a novel V-shaped 3-mirror ring resonator that allows two passes of the beams through the same nonlinear crystal. The pump is a 39 W hybrid Tm:fiber laser/Ho:YAG laser.

Quantum noise initiation and macroscopic fluctuations in optical parametric oscillators

The signals in an optical parametric oscillator (OPO) build up from quantum noise. In pulsed OPO’s this can lead to fluctuations in such macroscopic signal properties as rise time, pulse energy, frequency spectrum, and transverse profile. The strength of these fluctuations is investigated by use of simulation models that include quantum noise, multiple longitudinal modes, dispersion, birefringence, arbitrary output coupling, and transverse pump profile. The results are compared with results obtained with classical deterministic models to find out how well such models can estimate expectation values of signal observables.

Ultra-broadband chirped-pulse optical parametric amplifier with angularly dispersed beams

We propose a BBO-based chirped-pulse optical parametric amplifier employing an angularly dispersed signal beam to yield a full-octave gain bandwidth, sufficient for the direct amplification of sub-10-fs pulses. Numerical simulations show that this power-scalable amplifier configuration has a small-signal gain of 10(7) at a pumping intensity of 45 GW/cm(2). The additional phase-matching flexibility compared to alternative configurations permits the suppression of parasitic second harmonic generation of the signal beam.

High power and efficient long wave IR ZnGeP2 parametric oscillator

A high power, efficient, and tunable laser source in the 8-10 microm range, based on a ZnGeP(2) optical parametric oscillator (OPO) pumped by a hybrid 2.1 microm laser is demonstrated. The hybrid laser consists of a Q-switched Ho:YAG laser pumped by a 15 W CW thulium fiber laser. With 8.9 W of 2.1 microm pump power we obtained 0.95 W at 8 microm with an M(2)-value of 2.7 from an OPO with two walk-off compensating crystals.

Optical parametric master oscillator and power amplifier for efficient conversion of high-energy pulses with high beam quality

We describe a system for parametric conversion of high-energy,Q-switched laser pulses from 1.064 microm to 2.1 microm in KTiOPO(4). High beam quality and efficiency are obtained by use of a two-stage system: An optical parametric oscillator (OPO) pumped by a narrow beam with 8 mJ of energy, generates 1.9 mJ of signal energy for seeding an optical parametric amplifier (OPA). With 500 mJ pump energy, different OPA configurations produce up to 138 mJ signal energy with M(2) approximately 2.3.

Effect of idler absorption in pulsed optical parametric oscillators.

Absorption at the idler wavelength in an optical parametric oscillator (OPO) is often considered detrimental. We show through simulations that pulsed OPOs with significant idler absorption can perform better than OPOs with low idler absorption both in terms of conversion efficiency and beam quality. The main reason for this is reduced back conversion. We also show how the beam quality depends on the beam width and pump pulse length, and present scaling relations to use the example simulations for other pulsed nanosecond OPOs.