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We report on a cascade nanosecond CdSe optical parametric oscillator with an output energy of 0.54 mJ at 100 Hz, temperature tuning within 9245–9285 nm, and a narrow (∼6 cm−1) spectral width achieved by a volume Bragg grating acting on the first stage. The CdSe crystal is pumped intracavity by the signal wave from the PPKTP-based first stage, and both stages operate under noncritical phase-matching conditions. The simple, compact, and robust setup produced the highest overall conversion efficiency for an all-solid-state laser system based on CdSe with 1-μm pumping, and the corresponding quantum conversion efficiency exceeded 13%. [ABSTRACT FROM AUTHOR]

We report a self-phase-locked and degenerate backward wave optical parametric oscillator (BWOPO) generating a counterpropagating signal and an idler in the spectral band of optical communication. The device is based on a periodically poled Rb-doped KTiOPO4 crystal with a poling period of 433 nm. To the best of our knowledge, this is the shortest quasi-phase matching period reported in the bulk of a ferroelectric crystal. The spectral and coherence properties of the BWOPO at degeneracy are investigated. We observe a single pass conversion efficiency of 40%. At degeneracy, the counterpropagating signal and idler generate phase-matched sum-frequency generation in both directions. We confirm the phase-locked state at degeneracy by interfering the pump with the frequency-doubled backward wave. The phase-locked state is stable during the entire duration of the experiment without active stabilization. [ABSTRACT FROM AUTHOR]

REFERENCE 1 P. Mutter, A. Zukauskas, A.-L. Viotti, C. Canalias, and V. Pasiskevicius, "Phase-locked degenerate backward wave optical parametric oscillator", APL Photonics 8(2), 026104 (2023). AUTHOR DECLARATIONS Author Contribution C.C. and V.P. have contributed equally to this work. The original article[1] contains an error in the x axis labeling of Figs. [Extracted from the article]

A way to stabilize the domain structure in periodically poled Rb-doped KTiOPO4 samples at high-temperatures is presented. The domain contraction along the b-crystallographic axis that is observed when crystals are annealed at high temperatures is suppressed when the ends of the domains along the b-axis are diced away. Additionally, the thermal stability of self-assembled domain gratings with a sub-μm average periodicity of 650 ± 200 nm and a domain-width of 225 ± 75 nm in mm-thick samples is investigated, and it is shown that the key factor for the domain stability is the domain width rather than the interdomain distance. [ABSTRACT FROM AUTHOR]

We report on the development of a nanosecond mirrorless optical parametric oscillator (OPO) pumped at 1 μm. The gain medium of the OPO was periodically poled Rubidium-doped KTP with a grating period of Λ = 509 nm for the first order quasi-phase matching. For grating periods of this length, we demonstrate backward propagation of the signal field and forward propagation of the idler field. To the best of our knowledge, this is the first time such a counter-propagating geometry has been demonstrated in mirrorless OPOs. Pumping with a maximum energy of 6.48 mJ, the OPO yielded an overall conversion efficiency exceeding 53% with signal and idler energies of 1.96 mJ and 1.46 mJ, respectively. The generated signal and idler field spectra were measured to show narrowband linewidths on the order of 0.5 nm. We motivate that such a MOPO is ideal for seeding applications and discuss further improvements and work. [ABSTRACT FROM AUTHOR]

We study the thermal stability of domain walls in periodically poled Rb-doped KTP crystals. Domain-wall motion is observed after annealing the crystals above 550°C. This motion is highly anisotropic along the a- and b- crystallographic axes. Along the b-axis domain wall motion is in the order of tens of micrometers. In the a-direction, it results in either three orders of magnitude smaller domain wall displacement or in domain merging, depending on the initial domain configuration. We show that the thermal stability of the domain gratings depends on their periodicity, resulting in complete backswitching for sub-micrometer domains annealed at 730°C. [ABSTRACT FROM AUTHOR]

Self-starting and stable mode-locking of an Yb:KYW laser in the picoseconds pulse regime has been achieved by exploiting a positive cascaded Kerr lens in periodically poled KTP. The use of a volume Bragg grating (VBG), for locking the output spectrum of the laser, was essential to achieve a stable mode-locked operation in this wide gain bandwidth laser material. The laser emitted stable, nearly transform-limited pulses with a duration of 16 ps, at a repetition rate of 210 MHz, and with an energy of 3.2 nJ. The mode-locked spectrum was centred at 1,029.1 nm and featured a FWHM bandwidth of 85 pm, which was effectively determined by the VBG. Combination of a large cascaded Kerr nonlinearity with spectral limiting by a VBG represents so far the best opportunity for stable mode-locking of a broadband laser to produce near-transform-limited picosecond pulses. [ABSTRACT FROM AUTHOR]

An Yb:KYW laser intra-cavity frequency doubled to the green at 514.7 nm using a periodically poled Rb:KTP crystal with an output power exceeding 1 W is presented. Spectral narrowing and locking at the fundamental wavelength has been achieved by using a volume Bragg grating as the input coupler. [ABSTRACT FROM AUTHOR]

We present a simple technique for fabricating quasi-periodic bulk sub-μm ferroelectric domain gratings in Rb-doped KTiOPO4 (RKTP) based on self-organized ferroelectric domain formation. One-dimensional ferroelectric domain structures, with an average periodicity of 650 ± 200 nm and extending throughout 1 mm thick crystals, are obtained by etching and subsequent electric field poling using planar electrodes. The sub-μm structures in RKTP were used to demonstrate 5th order non-collinear quasi-phase matched backward second harmonic generation. [ABSTRACT FROM AUTHOR]

The article discusses a study of the high temperature (HT) behavior of ferroelectric domains in a periodically poled rubidium-doped potassium titanyl phosphate crystal by Bragg-Fresnel X-ray diffraction imaging. The authors invoked the generation of a built-in electric field in order to model and explain the development and partial disappearance of the inverted domain structure as the temperature increases. They found that at HT, the shape of the contrast image produced by the domains changed from straight parallel lines to a triangular inverted shape.

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%. [ABSTRACT FROM AUTHOR]

We present a differential absorption lidar (DIAL) laser transmitter concept designed around a Nested Cavity Optical Parametric Oscillator (NesCOPO) based Master Oscillator Power Amplifier (MOPA). The spectral bands are located around 2051 nm for CO2 probing and 1982 nm for H216O and HD16O water vapor isotopes. This laser is aimed at being integrated into an airborne lidar, intended to demonstrate future spaceborne instrument characteristics: high-energy (several tens of mJ nanosecond pulses) and high optical frequency stability (less than a few hundreds of kHz long term drift). For integration and efficiency purposes, the proposed design is oriented toward the use of state-of-the-art high aperture periodically poled nonlinear materials. This approach is supported by numerical calculations and preliminary experimental validations, showing that it is possible to achieve energies in the 40–50 mJ range, reaching the requirement levels for spaceborne Integrated Path Differential Absorption (IPDA) measurements. We also propose a frequency referencing technique based on beat note measurement of the laser signal with a self-stabilized optical frequency comb, which is expected to enable frequency measurement precisions better than a few 100 kHz over tens of seconds integration time, and will then be used to feed the cavity locking of the NesCOPO. [ABSTRACT FROM AUTHOR]