Nicky Thilmann

5 mm thick periodically poled Rb-doped KTP for high energy optical parametric frequency conversion

A 5 mm thick periodically poled bulk Rb-doped KTiOPO4 (KTP) crystal with a period of 38.86 μm was fabricated by electric field poling. Chemical etching and optical evaluation show a high quality of ...

Tunable Mid-infrared ZnGeP2 RISTRA OPO pumped by periodically-poled Rb:KTP optical parametric master-oscillator power amplifier

A laser-diode pumped Q-switched single-frequency Nd:YAG MOPA operating at 100 Hz was used to generate tunable mid-infrared radiation between 6.27 µm and 8.12 µm by employing a cascaded parametric arrangement consisting of degenerate parametric master-oscillator power amplifier using a large aperture periodically-poled Rb:KTiOPO4 which in turn pumped a ZnGeP2 (ZGP) nonplanar RISTRA OPO. The noncollinear ZGP RISTRA tuning behavior is elucidated. The device is aimed for minimally invasive surgery applications at 6.45 µm where the peak power of 193 kW in 5 ns pulses is demonstrated.

High-power, single-frequency, continuous-wave optical parametric oscillator employing a variable reflectivity volume Bragg grating

A continuous-wave singly-resonant optical parametric oscillator (SRO) with an optimum extraction efficiency, that can be adjusted independent of the pump power, is demonstrated. The scheme employs a variable-reflectivity volume Bragg grating (VBG) as the output coupler of a ring cavity, omitting any additional intra-cavity elements. In this configuration, we obtained a 75%-efficient SRO with a combined signal (19 W @ 1.55 µm) and idler (11 W @ 3.4 µm) output power of 30 W.

Nanosecond laser induced damage thresholds in KTiOPO4 and Rb:KTiOPO4 at 1 µm and 2 µm

Optimum design of high-energy cascaded parametric down-conversion schemes from 1 μm requires accurate knowledge of the laser induced damage threshold (LIDT) of the nonlinear crystal employed. We report surface LIDT measurements in KTiOPO4 (KTP) and Rb:KTP (RKTP) with nanosecond pulses at 1.064 μm and 2.1 μm. LIDT results for nanosecond pulses at 2 μm for KTP and RKTP have not been previously reported to the best of our knowledge.

Periodically poled KTiOAsO4 for highly efficient midinfrared optical parametric devices

We demonstrate high pattern-fidelity periodic poling of KTiOAsO4 at room temperature. The periodically poled crystal shows a deff of 10.1 pm/V and is used in an optical parametric oscillator pumped at 1064 nm to generate parametric radiation at 1538 and 3452 nm with a conversion efficiency of 45%.

Sub-nanosecond, 1-kHz, low-threshold, non-critical OPO based on periodically-poled KTP crystal pumped at 1064 nm

We employed a 9-mm long periodically-poled KTiOPO4 (PPKTP) crystal with a domain inversion period of 37.8 μm in an optical parametric oscillator (OPO) to generate sub-nanosecond pulses around 2.8 μm. With a 1-cm long OPO cavity in a singly resonant configuration with double pass pumping the OPO threshold was 110 μJ at 1064 nm (1-ns pump pulses at 1064 nm). The maximum idler output energy reached 110 μJ (quantum conversion efficiency of 32.5%). The signal pulse duration (FWHM) was 0.72 ns and the estimated idler pulse duration was 0.76 ns. At room temperature the signal and idler wavelengths were at 1722 and 2786 nm.

Study of a narrowband optical parametric oscillator at degeneracy with a transversely chirped Bragg grating

We investigate the energy and spectral properties of a narrowband (0.9 nm) optical parametric oscillator, tuneable around the degeneracy point from 1055 to 1066 nm, by usage of a transversely chirped volume Bragg grating.

Investigations of laser induced damage in KTiOPO4 and Rb:KTiOPO4 at 1 μm and 2 μm

One of the most practical means of generating tunable mid-infrared output is by using cascaded parametric downconversion from 1 μm, where efficient and reliable high-energy nanosecond lasers are well established. The overall efficiency of the cascade relies heavily on the efficiency of the first down-conversion stage where it is beneficial to employ quasi-phase matched crystals such as periodically-poled Rb:KTiOPO4 (PPRKTP). Ultimately, the pulse energy at 2 μm and the optimum design of the first cascade will depend on the maximum intensity which could be safely applied to these crystals and therefore these schemes mandate investigation of nanosecond laser-induced damage threshold in KTiOPO4 (KTP) and Rb:KTiOPO4 (RKTP) at 1.064 μm and 2 μm. In the context of high-energy systems, where the beams are at most loosely focused, the limiting energy fluence will be determined by the laser induced damage threshold (LIDT) of the bare surface. Therefore the LIDT of the bare surface is the lowest LIDT which has to be taken into account in design of robust 2 μm parametric systems. We report surface LIDT measurements in KTP and RKTP with nanosecond pulses at 1.064 μm and 2.1 μm. We find that the reported LIDT for the bulk is far higher than that of the surface and therefore is unsuitable as a guide for the 2 μm parametric system designs. LIDT values for KTP and RKTP with nanosecond pulses at 2 μm have not been reported so far to the best of our knowledge.

Mid-infrared cascaded parametric source in 6 μm region for medical applications

All-diode-pumped parametric source generating 5ns pulses tunable in 6.27μm-8.12μm with high-spatial-quality beam and the pulse energy of 0.9 mJ is demonstrated. The device exploits large-aperture PPRKTP MOPA for pumping ZGP OPO in a RISTRA cavity.

5 mm Thick Periodically Poled Rb:KTiOPO4 for High Power Optical Frequency Conversion

A periodically poled bulk Rb-doped KTiOPO 4crystal with 5 mm aperture was fabricated at room temperature. The ferroelectric domain structure is shown to be homogeneous across the whole aperture wit ...