KTiOAsO4 Crystal Research Articles

Broadly tunable femtosecond optical parametric amplifiers in the mid-infrared waveband based on cascaded noncollinear-collinear KTiOAsO4 crystals

We demonstrate a widely tunable, ultrafast optical parametric amplifier (OPA) based on cascaded noncollinear-collinear KTiOAsO4 (KTA) crystals seeded by a white light continuum (WLC) source in the mid-infrared waveband. We show that the parametric gain bandwidth of a collinear KTA crystal closely matches that of a noncollinear KTA crystal, thus avoiding the gain-bandwidth-mismatch-induced reduction of the frequency conversion-efficiency. In addition, we demonstrate the direct amplification of the WLC seed at up to 2.8 μm, which indeed offers a new technical route for manipulating the amplification bandwidth of ultrafast OPAs. This is, as far as we know, the first demonstration of direct amplification of the WLC light at this wave region with a 1-μm pump source.

Intense optical activation of Eu-doped KTiOAsO4 crystal induced by ion implantation

We report on the optical activation of Eu-doped KTiOAsO4 (KTA) by ion implantation and the effect on luminescence activity during lattice recovery. Optical activation of KTA crystals implanted with 400 keV Eu ions at an ion fluence of 5 × 1015 ions/cm2 is investigated. Despite a high damage level induced by the implantation, doping of Eu into KTA results in a strong photoluminescence in the temperature range from 4 K to 300 K, the strongest peak appears at 612 nm, which corresponding to the 5D0-7F2 transition. The lattice strain and Raman spectroscopy of the implanted KTA before and after annealing at 600°C and 700°C showed that the lattice defects are effectively recovered under annealing. Furthermore, the lattice damage effect on photoluminescence of ion-implanted Eu-doped KTA is negligible, indicating that ion implantation is an important method to obtain intense photoluminescence. The results reveal the optical activation properties of Eu implanted KTA and the attractiveness of its applications in waveguide quantum reservoirs.

Broadly tunable femtosecond OPA pumped by 1030 nm Yb: KGW laser with a range of non-linear crystals tested

We present a carrier-envelope phase-stable laser pulse source continuously tunable in the 2–4 µm wavelength range. The source relies on two-stage optical-parametric amplification, with the first stage pumped with the second harmonic of the 200-fs ytterbium pump laser. In contrast, the fundamental 1030 nm beam pumps the second stage directly. AgGaS2 (AGS), KTiOAsO4 (KTA), GaSe, LiGaS2 (LGS), and LiIO3 (LIO3) non-linear crystals were tested and the KTA crystal proved to be the most robust. We demonstrate operation without crystal damage at higher than previously reported peak intensities for AGS (290 GW/cm2) and LGS (214 GW/cm2) and report new values of damage threshold for GaSe (85 GW/cm2) and LIO3 (159 GW/cm2).

Double-pass pumping KTA OPO based on unstable resonator with Gaussian reflectivity mirror

A novel double-pass pumping optical parametric oscillator (OPO) with unstable resonator based on Gaussian reflectivity mirror (GRM) was proposed and demonstrated. The output characteristics of double-pass pumping OPO based on non-critical phase matching (NCPM) KTiOAsO4 (KTA) crystal were researched at a pulse repetition frequency of 100 Hz. Compared with the single-pass pumping OPO, the output energy and the conversion efficiency of double-pass pumping OPO were improved by 36 %. The beam qualities of signal and idler were measured and compared with different pump structures, and the results show that beam quality of signal for double-pass pumping OPO barely deteriorated. In addition, the pulse widths of signal and idler under two pumping structures and their variation trends with different pump energies were researched and compared.

Second harmonic generation in precisely diced KTiOAsO4 ridge waveguides

We demonstrate KTiOAsO4 (KTA) ridge optical waveguides by precise diamond blade dicing of ion-irradiated planar waveguides. The guiding and spectroscopic properties of ridge waveguides have been investigated. The original properties of the z-cut KTA crystal have been well preserved in the ion-irradiation area. Under optical excitation of a 1064-nm pulsed laser, second harmonic generation (SHG) of green laser at 532 nm is generated from waveguide structures, demonstrating a maximum output power of 1.71 mW and a SHG conversion efficiency of 4.28%. The results in this work suggest promising applications of diamond blade diced KTA waveguides in integrated photonics and nonlinear optics.

High energy picosecond mid-infrared optical parametric amplifier based on KTiOAsO4 crystal

A mJ-level picosecond mid-infrared (MIR) optical parametric amplifier (OPA) with a KTiOAsO4 (KTA) crystal was demonstrated for the first time. This MIR OPA was pumped by a 10 Hz, 30 ps, 1.06 μm Nd:YAG laser. The injection seed of MIR OPA was provided by a tunable near-infrared (NIR) OPG/OPA output with a β-BaB2O4 (BBO) crystal. The maximum idler energy of 1.85 mJ at 3.5 μm was obtained under a 20 mJ pumping energy at 1.06 μm. The pump to idler efficiency was 9.25%. The photon conversion efficiency was 30.4%. The 2.9–3.6 μm tuning performance of idler light in KTA-OPA was also investigated. The idler energies were 0.6 mJ at 2.9 μm and up to 1.4 mJ at 3.6 μm under a 14 mJ pumping energy at 1.06 μm. Moreover, the pulse temporal shape evolutions of the parametric lights in KTA-OPA process were simulated. The pulsewidth of the generated idler light was given.

Watt-level widely tunable femtosecond mid-infrared KTiOAsO4 optical parametric oscillator pumped by a 1.03 μm Yb:KGW laser.

A high-power, high-repetition-rate, broadband tunable femtosecond optical parametric oscillator (OPO) is constructed based on KTiOAsO4 crystal, pumped by a 75.5MHz mode-locked Yb:KGW laser. With 7W pump power, the OPO generates as much as 2.32W of signal power at 1.55μm and 1.31W of idler power at 3.05μm, corresponding to a total conversion efficiency of 51.8%. Operating at 151MHz repetition rate, the wavelength of the signal covers 1.41-1.71μm with a tunable idler range of 2.61-3.84μm. The idler bandwidth is more than 180nm over the entire mid-infrared range. By compensating intracavity dispersion, the signal pulse has a nearly Fourier transform-limited duration of 129fs at 1.52μm.

Efficient 1.7 μm light source based on KTA-OPO derived by Nd:YVO4 self-Raman laser.

An intra-cavity optical parametric oscillator (OPO) emitting at 1.7μm derived by Nd:YVO4 self-Raman laser is demonstrated in this Letter, with a KTiOAsO4 (KTA) crystal used as nonlinear optical crystal. A laser diode end-pumped acousto-optic Q-switched Nd:YVO4 self-Raman laser at 1176nm was employed as the pump source. At an incident pump power of 12.1W and a pulse repetition frequency of 60kHz, average output power up to 1.2W signal light at 1742nm was obtained, with diode-to-signal conversion efficiency of 10%. The pulse width was about 11ns and spectral line width was less than 0.5nm for the signal light. The results show that compact intra-cavity KTA-OPO derived by Nd:YVO4 self-Raman laser is an efficient method for 1.7μm waveband laser generation, with potential applications in biological imaging, laser therapy, special materials processing, etc.

An Experimental Study of Ultra-Wide-Band and Ultra-Wide-Aperture Non-Collinear Acousto-Optic Diffraction in an Optically Biaxial Potassium Arsenate Titanyl Crystal

Acousto-optic interaction in an optically biaxial crystalline medium under propagation of light close to one of the optical axes of a potassium arsenate titanyl KTiOAsO4 crystal has been studied. The experimental dependences of the intensity of a diffracted optical beam on the angle of light incidence on an ultrasonic wave have been obtained. It has been shown that a flat cut of a wave-vector surface provides development of an ultra-wide-aperture and ultra-wide-band acousto-optic deflector to control radiation in the visible and infrared electromagnetic spectral ranges.

Study of the possibility of using a parametric-light-generator-based laser system for lidar probing of the composition of the atmosphere

This paper discusses the possibility of using a laser system with parametric light generation based on a nonlinear KTiOAsO4 crystal for lidar probing of the atmosphere in the 3–4 μm range. A combined technique has been developed for lidar measurements of the gaseous components of the atmosphere, using the differential-absorption method (DAM) and differential optical absorption spectroscopy (DOAS). The DAM–DOAS technique has been tested in a numerical experiment to estimate the possibilities of lidar probing of minor gaseous components of the atmosphere.

Idler-resonant intracavity KTA-based OPO pumped by a dual-loss modulated-Q-switched-laser with AOM and Cr4+:YAG

An idler-resonant KTiOAsO4 (KTA)-based intracavity optical parametric oscillator (IOPO) pumped by a dual-loss-modulated Q-switched laser with an acousto-optic modulator (AOM) and a Cr4+:YAG saturable absorber (Cr4+:YAG-SA) has been presented. By utilizing a type-II non-critically phase-matched KTA crystal, signal wave at 1535 nm and idler wave at 3467 nm have been generated. Under an incident pump power of 18.3 W, maximum output powers of 615 mW for signal wave and 228 mW for idler wave were obtained at an AOM modulation rate of 10 kHz, corresponding to a whole optical-to-optical conversion efficiency of 4.6%. The shortest pulse widths of signal and idler wave were measured to be 898 ps and 2.9 ns, corresponding to the highest peak powers of 68.4 and 7.9 kW, respectively. In comparison with IOPO pumped by a singly Q-switched laser with an AOM, the IOPO pumped by a doubly Q-switched laser (DIOPO) with an AOM and a Cr4+:YAG-SA can generate signal wave and idler wave with shorter pulse width and higher peak power. By considering the spatial Gaussian distribution of intracavity photon density, a set of coupled rate equations for the idler-resonant DIOPO were built for the first time to the best of our knowledge. The simulation results agreed well with the experimental results.

Ridge Waveguides and Y-Branch Beam Splitters in KTiOAsO4 Crystal by 15 MeV Oxygen Ion Implantation and Femtosecond Laser Ablation

We report on the fabrication of ridge waveguides and Y-branch beam splitters in KTiOAsO4 nonlinear optical crystal by the combination of 15 MeV oxygen (O5+) ion implantation and femtosecond laser ablation. Guiding properties were investigated at the wavelengths of 633 and 808 nm, respectively, showing high polarization sensitivity of light propagation. Splitting ratios of these beam splitters are dependent on in-coupling alignment. The simulated guiding modal distributions of splitted guided beams, which was based on a reconstructed refractive index profile, shows reasonable consistence with the measured ones. After the stepwise annealing treatment at 473 and 573 K for 1 h each, the propagation losses for these guiding structures have been reduced considerably.

Tunable KTA Stokes laser based on stimulated polariton scattering and its intracavity frequency doubling.

This paper presents the tunable Stokes laser characteristics of KTiOAsO4 (KTA) crystal based on stimulated polariton scattering (SPS). When the pumping laser wavelength is 1064.2 nm, the KTA Stokes wave can be discontinuously tuned from 1077.9 to 1088.4 nm with four gaps from 1079.0 to 1080.1 nm, from 1080.8 to 1082.8 nm, from 1083.6 to 1085.5 nm, and from 1085.8 to 1086.8 nm. When a frequency doubling crystal LiB3O5 (LBO) is inserted into the Stokes laser cavity, the frequency-doubled wave can be discontinuously tuned from 539.0 to 539.5 nm, from 540.1 to 540.4 nm, from 541.3 to 541.8 nm, from 542.7 to 542.9 nm and from 543.4 to 544.2 nm. With a pumping pulse energy of 130.0 mJ and an output coupler reflectivity of about 30%, the obtained maximum Stokes laser pulse energy at 1078.6 nm is 33.9 mJ and the obtained maximum frequency-doubled laser pulse energy at 543.8 nm is 15.7 mJ. By using the most probably coupled transverse optical modes obtained from the literature, the polariton refractive indexes, and the simplified polariton Sellmeier equations, the polariton dispersion curve is obtained. The formation of the Stokes frequency gaps is explained.

A high energy 3.75 μm KTA optical parametric oscillator at a critical angle

A high energy 3.75 μm nano-second KTiOAsO4 (KTA) optical parametric oscillator (OPO) at a critical angle is demonstrated in this letter. The OPO is pumped by a 1.064 μm laser and the KTA crystal is cut at 41.2° in the XZ plane. The phase matching angle is at the edge of the phase match curve and the edge of the absorption region for mid-infrared lasers. The cavity is a signal resonant oscillator. The spatial distribution of the pump light is a quasi-plane wave and the pulse width is 10 ns. A 218 mJ signal at 1.484 μm and a 60 mJ idler at 3.75 μm are achieved with a pump energy of 795 mJ, corresponding to a conversion efficiency of 35%. The idler pulse width is 7 ns. The divergence angle in the walk-off plane is 4 mrad and it is 14 mrad in the other plane. The results prove that the OPO phase matching of KTA exists at 3.75 μm and the KTA OPO can generate a high energy idler at 3.75 μm.

Distribution, damage, and blue luminescence of Tm ion implanted into KTiOAsO4 crystal

Potassium titanyl arsenate (KTiOAsO4 or KTA) crystal was ion implanted by 500keV Tm+ ions with a fluence of 5.5×1014ions/cm2 at room temperature. The depth profile of implanted Tm+ ions into KTiOAsO4 crystal was measured by Rutherford backscattering spectrometry and calculated by the stopping and ranges of ions in matter (SRIM'2006) computer code. The results of SRIM'2006 calculation and X-ray diffraction analysis show that the surface of KTA crystal was almost amorphous state due to the Tm+ ion implantation. The excitation and emission spectrum of Tm implanted KTA at room temperature were measured. The visible emission spectrum consists of a main contribution in the blue region at 467nm corresponding to the Tm transition from the 1D2 to the 3F4 ground state.

Idler-resonant optical parametric oscillator based on KTiOAsO4

An idler-resonant KTiOAsO4 (KTA) optical parametric oscillator is demonstrated within a diode-end-pumped acousto-optically Q-switched Nd:YAG laser. With an X-cut KTA crystal, idler wave at 3467 nm and signal wave at 1535 nm are generated. Under an incident diode pump power of 15.4 W, the idler output power of 105 mW and signal power of 720 mW are obtained at a pulse repetition rate of 40 kHz. The pulse widths of the idler and signal waves are 7.2 and 3.1 ns, respectively. The beam quality factors (M2) of the idler wave are within 1.2 in both horizontal and vertical directions.

Ion implantation, annealing diffusion and photoluminescence of Er in KTiOAsO4 crystals

The KTiOAsO4 crystals have been implanted with 500keV Er ions at a fluence of 3.0×1015ions/cm2 with the aim of optically doping the material in the near surface region. By combing the Stopping and Range of Ions in Matter results and X-ray diffraction results, we may conclude that the surface of the KTiOAsO4 crystal suffered serious damage after Er+ ion implantation. The depth distribution and annealing diffusion behavior of Er atoms were determined using the Rutherford backscattering technique. Photoluminescence emission at room temperature with a wavelength of 1540nm was observed in the annealed sample.

Theoretical and experimental studies on passively Q-switched KTiOAsO4 optical parametric oscillator

A passively Q-switched intracavity optical parametric oscillator based on KTiOAsO4 (KTA) crystal is studied theoretically and experimentally. The rate-equation-based theoretical model is established to describe the time evolutions of the population inversion density of the laser crystal, ground-state population density of the saturable absorber, fundamental photon density, signal photon density and the idler photon density. In the experiment, a laser diode-end pumped, passively Q-switched Nd:YAG/KTA IOPO with a Cr4+:YAG crystal as the saturable absorber is realized to verify this model. The characteristics including the output power, the pulse repetition rate, the pulse width and the beam quality were investigated for this OPO. The experimental results for the output power and the repetition rate agree with the theory well. And both results show that with same pumping level the idler pulse width is shorter than the signal one.

Optical Channel Waveguide in KTiOAsO$_{4}$ Crystals Produced by O$^{+}$ion Implantation

We report on the fabrication and characterization of optical channel waveguide in x-cut KTiOAsO4 crystal produced by photographic masking and following direct O ion implantation at energy of 3.0 MeV and fluence of 5 × 1013 ions/cm2. Positive changes of both and refractive indices (corresponding TM and TE polarized light respectively) in the waveguide region are responsible for light waveguiding. After annealing treatment, the propagation losses of the waveguide could be reduced to 1.2 dB/cm, exhibiting acceptable guiding properties.

Intracavity KTiOAsO4 optical parametric oscillator pumped by an actively Q-switched Nd:YAG laser

A KTiOAsO4 (KTA) intracavity optical parametric oscillator (IOPO) is achieved within a diode end-pumped acousto-optically Q-switched Nd:YAG laser. With a 25-mm-long X-cut KTA crystal, efficient parametric conversions to signal (1535 nm) and idler (3467 nm) waves are realized. At an incident diode power of 14.9 W, the highest output power of 1.83 W including 1.37 W of signal and 0.46 W of idler radiations are obtained at a repetition rate of 40 kHz, corresponding to a total optical-to-optical conversion efficiency of 12.3%. Rate equations model are used to simulate this system, and the theoretical results agree with the experimental ones.