Riaan Stuart Coetzee

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.

7.3-10.5 µm Tunable Single-frequency Parametric Source for Standoff Detection of Gaseous Chemicals

We report on the first single-frequency parametric source tunable in the longwave infrared with an output energy of 1 mJ. The source is then used in a lidar to detect chemicals in the vapor phase.

Spatial and temporal coherence in optical parametric devices pumped with multimode beams

We investigate the emergence of spatial and temporal coherence for the fields in the noncritical nondegenerate parametric second-order down-conversion process pumped with low spatial and temporal coherence beams. It is shown that in this scenario, which is of considerable practical importance, the parametric gain in the near field breaks down into an ensemble of mutually incoherent beamlets containing parametric waves. The field generated in a single beamlet is fully spatially coherent. The size of such coherent parametric gain regions is governed by the near-field spatial coherence radius of the pump, which also acts as a parameter, restraining the linear diffraction of the parametric waves generated in the nonlinear interaction. Furthermore, we experimentally demonstrate how the spatial and temporal coherence can be substantially enhanced by manipulating the spatial field correlation of the multilongitudinal and multi-transversal mode pump.

Periodically Poled KTP with Sub-wavelength Periodicity: Nonlinear Optical Interactions with Counter Propagating Waves

We present the recent development on periodically poled nonlinear crystals with subwavelength periodicities as short as 500 nm. These devices show conversion efficiencies larger than 45%. Their uni ...

Low-threshold, mid-infrared backward-wave parametric oscillator with periodically poled Rb:KTP

We report on the development of a nanosecond mirrorless optical parametric oscillator (OPO) pumped at 1 mu m. The gain medium of the OPO was periodically poled Rubidium-doped KTP with a grating per ...

70 mJ single-frequency parametric source tunable between 1.87–1.93 μm and 2.37–2.47 μm for difference frequency generation in the LWIR

Detection of chemical species using differential absorption lidar is a topic of growing interest for safety in petrochemical facilities, outdoor air quality measurements, greenhouse gases monitoring from space, and standoff detection of toxic chemical plumes. In such a lidar the optical source must combine a high energy (> 10 mJ for range-resolved detection), a wide and arbitrary wavelength tunability, and a very narrow linewidth (<0.1 cm−1 or even single-frequency for the most demanding applications). In the longwave infrared (8–12 μm), this challenge is even more difficult due to the scarcity of mature optical components. Here, we propose a solution based on optical parametric conversion, using a master-oscillator power-amplifier (MOPA) concept. The design, shown in Fig.1, follows our previous work on a high-energy single-frequency emitter near 2 μm [1], and is similar to one previously proposed for LWIR emission [2].

An efficient, 2 µm optical parametric amplifier based on large-aperture periodically poled Rb:KTP

High-energy mid-infrared nanosecond sources are required in a number of applications including biomedicine, remote sensing, and standoff countermeasures, to name just a few. Sources which serve these applications include mid-infrared fiber and solid-state lasers, quantum cascade lasers, as well as optical parametric oscillators (OPO).

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.