Helge Fonnum

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.

Mid-infrared source with 0.2 J pulse energy based on nonlinear conversion of Q-switched pulses in ZnGeP2.

Mid-infrared (3-5 μm) pulses with high energy are produced using nonlinear conversion in a ZnGeP(2)-based master oscillator-power amplifier, pumped by a Q-switched cryogenic Ho:YLF oscillator. The master oscillator is based on an optical parametric oscillator with a V-shaped 3-mirror ring resonator, and the power amplifier is based on optical parametric amplification in large-aperture ZnGeP(2) crystals. Pulses with up to 212 mJ energy at 1 Hz repetition rate are obtained, with FWHM duration 15 ns and beam quality M(2) = 3.

Mid-infrared optical parametric oscillator synchronously pumped by an erbium-doped fiber laser

A mid-infrared synchronously pumped optical parametric oscillator pumped by a femtosecond erbium-doped fiber laser is demonstrated and characterised. The idler is tunable from 3.7-4.7 μm, with a maximum average power of 37 mW and a pulse length of ∼ 480 fs at 4 μm. We compare the experimental results with numerical results based on an extensive simulation model.

250-MHz synchronously pumped optical parametric oscillator at 2.25–2.6 μm and 4.1–4.9 μm

A compact and versatile femtosecond mid-IR source is presented, based on an optical parametric oscillator (OPO) synchronously pumped by a commercial 250-MHz Er:fiber laser. The mid-IR spectrum can be tuned in the range 2.25-2.6 μm (signal) and 4.1-4.9 μm (idler), with average power from 20 to 60 mW. At 2.5 μm a minimum pulse duration of 110 fs and a power of 40 mW have been obtained. Active stabilization of the OPO cavity length has been achieved in the whole tuning range.

High power multi-wavelength infrared source

μWe report on a high-power semi-ruggedized laser source, which can deliver radiation in all infrared transmission bands from 2 to 10 μm. In the source a 70 W Tm-doped fiber laser pumps a Q-switched Ho:YAG laser, which produces 37 W of output power at 2.1 μm. The Ho-laser pumps two ZnGeP2 OPOs. The first generates a combined power of 14 W at 3.9 μm and 4.5 μm, and the second generates watt-level outputs at 2.8 μm and 8 μm. The OPOs have a novel V-shaped 3-mirror ring resonator design, which gives high efficiency and beam quality.

Laser source with high pulse energy at 3-5 μm and 8-12 μm based on nonlinear conversion in ZnGeP2

We present a high energy infrared laser source where a Tm:fiber laser is used to pump a high-energy 2-μm cryogenically cooled Ho:YLF laser. We have achieved 550 mJ of output energy at 2.05 μm, and through non-linear conversion in ZnGeP2 generated 200 mJ in the 3-5-μm range. Using a numerical simulation tool we have also investigated a setup which should generate more than 70 mJ in the 8-12-μm range. The conversion stage uses a master-oscillator-power-amplifier architecture to enable high conversion efficiency and good beam quality.

Fiber laser pumped high energy cryogenically cooled Ho:YLF laser

In this paper we report on a high energy, low repetition rate 2-micron-laser, with high conversion efficiency in terms of output energy per pump power. The laser consists of a Ho3+-doped LiYF4 (YLF) crystal cooled to cryogenic temperatures in an unstable resonator, pumped by a thulium fiber laser. The cooling to 77 K makes Ho:YLF a quasi four level laser system, which greatly enhances the extraction efficiency. We achieved 356 mJ in Q-switched operation at 1 Hz PRF when pumping the laser with 58 W for 36 ms. The high beam quality from the fiber laser and the use of an unstable resonator with a graded reflectivity mirror (GRM) resulted in a high quality laser beam with a M2-value of 1.3.

Measurements of IR propagation in the marine boundary layer in warm and humid atmospheric conditions

A multinational field trial (SAPPHIRE) was performed at the Chesapeake Bay, USA, during June 2006 to study infrared ship signature and atmospheric propagation effects close to the sea surface in a warm and humid environment. In this paper infrared camera recordings of both land and ship mounted sources are analyzed. The cameras were positioned about 4 m above mean sea level. Several meteorology stations - mounted on land, on a pier and on a buoy - were used to characterize the propagation environment, while sensor heights were logged continuously. Both sub- and superrefractive conditions were studied. Measurements are compared to results from earlier field trials performed in Norway during typical North-Atlantic atmospheric conditions (cool air with little water content), and differences between medium wave and long wave infrared are emphasized. The ship mounted source - a calibrated blackbody source - was used to study contrast intensity and intensity fluctuations as a function of distance. The distance to the apparent horizon is also determined. In addition, normalized variance of intensity for land based sources has been calculated for a number of cases and these values can easily be converted to refractive index structure constant C2n-values. Measurement results are compared to results from the IR Boundary Layer Effects Model (IRBLEM).

Optical Parametric Oscillator At 8 µm With High Pulse Energy And Good Beam Quality

1.8 mJ pulse energy at 8 µm is demonstrated from a ZnGeP2-based optical parametric oscillator with V-shaped ring resonator, pumped with a Ho:YLF laser. The 8 µm output has a beam quality of M2 = 2.6.

Mid-infrared ZnGeP 2 -based source with 0.2 J pulse energy

Mid-infrared (3-5 μm) pulses with up to 207 mJ energy at 1 Hz repetition rate are produced using nonlinear conversion in a ZnGeP2-based master oscillator-power amplifier, pumped by a cryogenic Ho:YLF oscillator.