2.7 μm backward wave optical parametric oscillator source for CO spectroscopy.

In this work, a novel 2.7 µm source used for CO and HO vapor spectroscopy using the backward propagating wave of a backward wave optical parametric oscillator (BWOPO) is demonstrated for the first time to our knowledge. The unique properties of BWOPOs eliminate the need for additional spectral narrowing or wavelength stabilization, enabling the use of a multi-longitudinal mode Q-switched pump laser centered around 1030 nm.

High-contrast coercive field engineering for periodic poling of RbKTiOPO with Ba/K ion-exchange.

We investigate a new method of coercive field engineering for periodic poling of RbKTiOPO (RKTP). By ion exchanging RKTP in a molten salt containing 7 mol% Ba(NO) and 93 mol% KNO we achieve more than an order of magnitude difference in polarization switching time between the exchanged and non-exchanged regions. This method is used to fabricate periodic gratings of 2.

Narrowband, intracavity-pumped, type-II BaGaGeSe optical parametric oscillator.

We present a tunable (6.62-11.34 µm), singly-resonant, cascade optical parametric oscillator with intracavity pumping of BaGaGeSe in the second stage and spectral narrowing realized by a Volume Bragg Grating acting on the signal wave of the first stage which serves as a pump for the second stage.

Highly efficient, high average power, narrowband, pump-tunable BWOPO.

We demonstrate a continuously tunable mid-infrared source that produces narrowband radiation at 1981 nm and 2145 nm based on a tunable Yb-based hybrid MOPA pump and a backward-wave optical parametric oscillator (BWOPO). The BWOPO employs a PPRKTP crystal with 580 nm domain periodicity. The BWOPO has a record-low oscillation threshold of 19.

Multi-transversal mode pumping of narrow-bandwidth backward wave optical parametric oscillator.

A stable, narrow-bandwidth (274 MHz) backward wave optical parametric oscillator (BWOPO) generating mJ-level backward signal at 1885nm and forward idler at 2495 nm is presented. The BWOPO was pumped by a single-longitudinal mode, Q-switched Nd:YAG high-energy laser at 1064 nm. We show that multi-transversal mode pumping leads to the spectral broadening of the BWOPO backward signal and the generation of nanosecond pulses 2.

Efficient first-order quasi-phase-matched backward second-harmonic generation.

We demonstrate first-order quasi-phase-matched backward second-harmonic generation (BSHG) with an efficiency of 18.7%. This represents an increase by two orders of magnitude from earlier experiments employing higher-order quasi-phase-matching.

Intra-cavity dark pulse generation through synchronized sum-frequency mixing.

A Nd:YVO laser operating at 1064 nm generating a stable mode-locked train of 10 ps-long dark pulses with a 211 MHz repetition rate is presented. The mode-locking relies on a periodic loss modulation produced by intra-cavity sum-frequency mixing with a synchronous bright-pulse train from a mode-locked femtosecond Yb:KYW laser at 1040 nm. A modulation depth of 90% was achieved for the dark pulses, confirmed by cross-correlation measurements.

µJ-level multi-cycle terahertz generation in a periodically poled Rb:KTP crystal.

We demonstrate multi-cycle terahertz (MC-THz) generation in a 15.5 mm long periodically poled rubidium (Rb)-doped potassium titanyl phosphate (Rb:PPKTP) crystal with a poling period of 300 µm. By cryogenically cooling the crystal to 77 K, up to 0.

Ion-exchanged waveguides in periodically poled Rb-doped KTiOPO for efficient second harmonic generation.

An ion-exchange process has been developed for periodically poled Rb-doped KTiOPO (RKTP) which warrants high efficiency and low loss channel waveguides. The domain stability was investigated, and it was found that domain gratings with uncharged walls could stand the ion-exchange process without deterioration. 3.

Development and experimental demonstration of negative first-order quasi-phase matching in a periodically poled Rb-doped KTiOPO crystal.

We worked on a new scheme of quasi-phase matching (QPM) based on the negative first order of the spatial modulation of the sign of the second-order nonlinearity. Applying this scheme in the case of angular-QPM (AQPM) in a biaxial crystal reveals new directions of propagation for efficient parametric frequency conversion as well as "giant" spectral acceptances. The experimental validation is performed in a periodically poled rubidium-doped biaxial crystal.

Coherent phase transfer and pulse compression at 1.4 μm in a backward-wave OPO.

The frequency modulation transfer property of a backward-wave optical parametric oscillator (BWOPO) is investigated in the context of near-IR pulse compression. The maximum transferrable bandwidth from the pump to the forward wave in a BWOPO is determined by the group dispersion mismatch. In comparison, the third-order phase introduced in a single-grating compressor setup is more detrimental to achieve optimum compression of the BWOPO forward wave.

Narrowband, tunable, infrared radiation by parametric amplification of a chirped backward-wave OPO signal.

The strict momentum conservation constraints for backward-wave optical parametric oscillators (BWOPOs) gives an inherently narrowband backward-generated wave, even with broadband pumping. Unfortunately, the limited tuning range of this wave restricts potential applications. Here we demonstrate a method to circumvent this restriction and increase the tuning range by more than one order of magnitude.

Validation of the angular quasi-phase-matching theory for the biaxial optical class using PPRKTP.

We report the first experimental validation of angular quasi-phase-matching (AQPM) theory in a biaxial crystal by performing second-harmonic generation (SHG) in the periodically-poled Rb-doped KTiOPO (PPRKTP) crystal cut as a sphere. Both AQPM and birefringence phase-matching (BPM) angles were measured thanks to a Kappa circle.

Counter-propagating parametric interaction with phonon-polaritons in periodically poled KTiOPO.

Strongly enhanced backward stimulated polariton scattering (BSPS) is demonstrated in periodically-poled KTiOPO (KTP) crystals with a high power-conversion efficiency up to 70%. We study the physical mechanism of such counter-propagating parametric interaction with phonon-polaritons in χ modulated structures. BSPS is a three-wave mixing that is distinguished from backward stimulated Raman scattering (BSRS), while a strong absorption at large polariton wave-vectors can still make BSPS display certain characteristics of BSRS such as self-compression of the Stokes pulse.

Highly efficient mirrorless optical parametric oscillator pumped by nanosecond pulses.

A highly efficient mirrorless optical parametric oscillator (MOPO), pumped by narrowband nanosecond pulses at 1064 nm, is demonstrated. The MOPO is based on quasi-phase-matched parametric interaction of counter-propagating photons in 1-mm-thick periodically poled Rb-doped KTiOPO crystal with a period of 755 nm. It generates a co-propagating signal at 1740 nm and a counter-propagating idler at 2741 nm, achieving mJ-level output with a total signal-and-idler conversion efficiency of 47%.

Cascaded counter-propagating nonlinear interactions in highly-efficient sub-µm periodically poled crystals.

Mirrorless optical parametric oscillators (MOPOs) are very attractive parametric devices that rely on the nonlinear interaction of counter-propagating photons to inherently establish distributed feedback, without the use of external mirrors or surface coatings. These devices offer unique spectral and coherence properties that will benefit a large variety of applications ranging from spectroscopy to quantum communications. The major obstacle in exploiting their full potential is ascribed to the difficulty in engineering a nonlinear material in which the generation of counter-propagating waves can be phase matched.

Intracavity difference-frequency mixing of optical parametric oscillator signal and idler pulses in BaGaSe.

An overall quantum conversion efficiency of 7.8% is achieved by intracavity mixing the signal and idler of a 1.064 μm pumped Rb:PPKTP optical parametric oscillator in BaGaSe.

Fully-resonant, tunable, monolithic frequency conversion as a coherent UVA source.

We demonstrate a monolithic frequency converter incorporating up to four tuning degrees of freedom, three temperature and one strain, allowing resonance of pump and generated wavelengths simultaneous with optimal phase-matching. With a Rb-doped periodically-poled potassium titanyl phosphate (KTP) implementation, we demonstrate efficient continuous-wave second harmonic generation from 795 to 397, with low-power efficiency of 72% and high-power slope efficiency of 4.5%.

Terahertz parametric generation and amplification from potassium titanyl phosphate in comparison with lithium niobate and lithium tantalate.

We report superior terahertz parametric generation from potassium titanyl phosphate (KTP) over congruent-grown lithium niobate (CLN) and lithium tantalate (CLT) in terms of parametric gain and laser damage resistance. Under the same pump and crystal configurations, the signal emerged first from KTP, 5% Mg-doped CLN, CLN, and then finally from CLT. The signal growth rate in KTP was comparable to that in 5%-Mg-doped CLN, but the signal power from KTP reached a much higher value after all the other crystals were damaged by the pump laser.

Rb:PPKTP optical parametric oscillator with intracavity difference-frequency generation in AgGaSe.

A 1.064 μm pumped Rb:PPKTP optical parametric oscillator (OPO) generates mid-IR radiation by intracavity mixing the resonant signal and idler waves in AgGaSe. The ∼6  ns pulses at ∼7  μm have an energy of 670 μJ at 100 Hz, equivalent to an average power of 67 mW.

Intracavity-pumped, cascaded AgGaSe₂ optical parametric oscillator tunable from 5.8 to 18 µm.

A AgGaSe2 nonlinear crystal placed in a coupled cavity is intracavity pumped by the ~1.85-µm signal pulses of a 1.064-µm pumped Rb:PPKTP doubly-resonant optical parametric oscillator (OPO) operating at a repetition rate of 100 Hz.

Studies of sub-millisecond domain dynamics in periodically poled Rb-doped KTiOPO(4), using online in situ second harmonic generation.

The temporal evolution of in situ second-harmonic generation was employed to study domain dynamics during periodic poling in Rb-doped KTP. With this method we investigated the influence of various poling parameters, including electric-field pulse shape, pulse magnitude, and number of pulses, on the quality of the QPM structure. It was found that the grating formation can be a sub-millisecond process and the benefits of using symmetric triangular electric-field pulse shape over square pulse shape in the single-pulse poling regime were demonstrated.

Contact poling of Rb:KTiOPO(4) using a micro-structured silicon electrode.

A contact poling technique for domain engineering of ferroelectrics using a micro-structured silicon electrode is demonstrated on Rb:KTiOPO. High quality QPM gratings were reproducibly fabricated. The silicon electrode is reusable and the technique potentially suitable when complex structures with sub-μm features are to be domain engineered, which otherwise is incompatible with conventional photolithography.

High-power continuous-wave frequency-doubling in KTiOAsO4.

High-power continuous-wave generation at 533 nm is demonstrated in bulk periodically poled KTiOAsO(4) (KTA) by single-pass frequency doubling of a VBG-locked Yb-doped fiber laser. Absorption characteristic and second harmonic generation (SHG) performance of different KTA samples are studied and compared. The best performing sample catered for 25%-efficient SHG of 13.

Second-harmonic generation in periodically poled bulk Rb-doped KTiOPO₄ below 400 nm at high peak-intensities.

We demonstrate that bulk Rb-doped KTiOPO₄ (RKTP) shows improved susceptibility to gray-tracking compared to flux-grown KTiOPO₄ . We show high-fidelity periodic poling of 1 mm thick RKTP with a period of 3.18 µm for second harmonic generation at 398 nm with a normalized conversion efficiency of 1.