KTP Crystal Research Articles

近红外光谱区光子晶体禁带与KTP缺陷研究

近红外光谱区光子晶体禁带与KTP缺陷研究

近红外光谱区光子晶体禁带与KTP缺陷研究

近红外光谱区光子晶体禁带与KTP缺陷研究

高峰值功率皮秒超短脉冲抽运KTP晶体倍频研究

高峰值功率皮秒超短脉冲抽运KTP晶体倍频研究

Incorporation of hafnium (IV) into KTP framework from phosphate‐fluoride fluxes

Solid solutions KTi1‐XHfXOPO4 (х = 0.008 – 0.107) possessing the KTiOPO4 structure, have been synthesized in molten system K2O‐P2O5‐TiO2‐HfF4. The crystal growth experiment of Hf‐doped KTP crystal has been reported. The X‐ray powder diffraction data and chemical analysis are also presented. It has been shown that KTiOPO4 crystal structure slightly changes when Hf incorporates into the framework. Transmission/absorption spectra of KTi0.974Hf0.026OPO4 crystals have been recorded. The incorporation of Hf ions shifts the optical absorption edge in the UV‐visible spectrum towards the long‐wavelength region with absorption near 387 nm.

Nonstoichiometry in KTP and Nb: KTP crystals by high-temperature solutions method

Nonstoichiometry could cause many point defects and limit the application of KTP crystal. Nonstoichiometry in KTP and Nb:KTP crystals by high-temperature solution method were studied by laser-ablation inductively coupled plasma mass spectometry (LA-ICP-MS) and X-ray photoelectron spectroscopy (XPS). The formation of high potassium and Ti[Formula: see text] centers in KTP and Nb:KTP crystals was analyzed. The effect of niobium on nonstoichiometry in Nb:KTP crystal was discussed. The results showed that high potassium, low phosphate, and low oxygen existed in KTP and Nb:KTP crystal samples. Low phosphate and low oxygen in crystal samples resulted from phosphate volatilization, which could be inhibited by the increase of niobium content. Meanwhile, Ti[Formula: see text] centers in crystal samples were original and formed during crystal growth, and were generated with high potassium simultaneously.

Powerful 3μm YSGG:Cr : Er and YSGG: Cr :Yb : Ho Q-Switched Lasers Operating in the Repetition-Rate Mode

We construct Q-switched megawatt-power level YSGG:Cr : Er and YSGG: Cr :Yb : Ho lasers operating in the repetition-rate mode of generation. We obtain the maximum output of 140 mJ at 1Hz and an output energy of 40 mJ in a Gaussian-like mode with a repetition rate of 5 and 10 Hz. The minimum pulse width is measured to be 50 ns. We discuss the influence of the repetition rate on the output energy and prove that a KTP crystal can be used as the electro-optic Q-switch for an YSGG:Cr : Yb :Ho laser. We achieve a 50 mJ pulse energy with 50 ns pulse width. We propose and implement a hybrid scheme of pulse-periodic two-wave generation of giant pulses in the cavity where the YSGG: Cr :Er and YSGG:Cr : Yb :Ho crystals are arranged sequentially, and Q-switching is performed using frustrated total internal reflection (FTIR). Simultaneously, we observe powerful generation at 2.79 and 2.8 μm. We discuss the possibility to implement a hybrid solid-state YSGG:Cr : Er–YSGG :Cr : Yb :Ho laser for THz generation and other applications.

High-order Stokes generation in a KTP Raman laser pumped by a passively Q-switched ND:YLF laser

High-order Stokes wave was observed in an x-cut KTP crystal based on stimulated Raman scattering (SRS) pumped by a passively Q-switched Nd:YLF laser with a Cr4+:YAG saturable absorber. Output spectra including the fundamental wave at 1047nm and six Stokes wavelengths at 1077nm, 1110nm, 1130nm, 1143nm, 1164nm, 1180nm based on two Raman frequency shift at 267.4cm−1 and 693.0cm−1 were obtained simultaneously. We also detected green light generation with output power of 12mW from self frequency mixing in the KTP crystal. The maximum total output power reached 452mW at the repetition frequency of 8.1kHz, corresponding to the optical-to-optical conversion efficiency of 4.61% and pump-to-Raman conversion efficiency of 3.6%.

Flux growth and grey colouration characteristics in KTiOPO4:Ln (Ln= Yb, Nd, Ho, Er, La)

Single crystals of KTiOPO4:Ln (Ln=Yb, Nd, Ho, Er and La) were successfully grown by the top seeded solution growth (TSSG) method using potassium polyphosphate as a flux. A series of rare earth metal (Yb, Nd, Ho, Er and La) doped KTP crystals was subjected to high electric field and hydrogen annealing treatment at 973K temperature. The vital role of alkali ionic conduction and Ti3+ in colouration of KTP has been studied by permittivity and ac conductivity studies. The hydrogen anneal- and UV bleach-induced grey colouration was studied by absorption and transmittance characteristics. The structural changes induced by grey tracking on KTP:Ln were studied by Raman shift analysis. The oxygen vacancies or Ti3+ centres were created by various treatments and the degree of colouration in the crystal was evaluated. The mechanisms of colouration in the crystal and resistance behaviour of grey colouration by lanthanide doping were studied.

Diode-Pumped Nd:KGd(WO4)2 Laser: Lasing at Fundamental and Second Harmonic Frequencies

High-power cw and quasi-cw lasing at the fundamental and second harmonic frequencies is obtained from Nd:KGd(WO 4 ) 2 lasers based on Np- and Ng-cut crystals pumped longitudinally by a diode laser at 879 nm. Because of different crystal lengths, the limiting pump power beyond which the crystals undergo thermomechanical damage is 26.8 W for the N p -cut and 17.3 W for the N g -cut. At these pump powers the cw outputs at λ = 1067.2 nm are 9.4 and 5.4 W, respectively, and the N g -cut crystal output is TEM 00 at the fundamental frequency. With quasicontinuous pumping at a 10% duty cycle the instantaneous laser power reaches ~11 W for both cuts with a periodic duration of 10–20 ms. The differential lasing efficiency relative to the absorbed pump power is 66.4% for cw lasing and 77.4% for quasi-cw operation. With intracavity frequency doubling using a KTP crystal, better results were obtained with the N g -cut crystal because of its simpler thermal lensing. The maximum second harmonic power was ~1.1 W for cw operation and ~2.6 W for quasi-cw operation with a diode laser power of 27.3 W.

Thermal stability of ferroelectric domain gratings in Rb-doped KTP

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.

Generalized Jones matrix method for homogeneous biaxial samples.

The generalized Jones matrix (GJM) is a recently introduced tool to describe linear transformations of three-dimensional light fields. Based on this framework, a specific method for obtaining the GJM of uniaxial anisotropic media was recently presented. However, the GJM of biaxial media had not been tackled so far, as the previous method made use of a simplified rotation matrix that lacks a degree of freedom in the three-dimensional rotation, thus being not suitable for calculating the GJM of biaxial media. In this work we propose a general method to derive the GJM of arbitrarily-oriented homogeneous biaxial media. It is based on the differential generalized Jones matrix (dGJM), which is the three-dimensional counterpart of the conventional differential Jones matrix. We show that the dGJM provides a simple and elegant way to describe uniaxial and biaxial media, with the capacity to model multiple simultaneous optical effects. The practical usefulness of this method is illustrated by the GJM modeling of the polarimetric properties of a negative uniaxial KDP crystal and a biaxial KTP crystal for any three-dimensional sample orientation. The results show that this method constitutes an advantageous and straightforward way to model biaxial media, which show a growing relevance for many interesting applications.

The effect of cooling rate on size, quality and morphology of KTiOPO4 (KTP) crystals grown by different nucleation techniques

KTP crystals have been grown by two nucleation techniques namely spontaneous nucleation in flux medium and nucleation on Pt rod using K6P4O13 flux.10 °C/h, 7 °C/h, 0.8 °C/h, 0.4 °C/h and 0.2 °C/h cooling rates were applied for spontaneous nucleation and crystals up to 15 × 7 × 4 mm3 in size were grown. 1 °C/h and 0.8 °C/h cooling rates were also used for nucleation on Pt rod and crystals up to 8 × 6 × 3 mm3 in size were grown. The effect of cooling rate on size, morphology and optical quality of grown crystals by both techniques were studied. For nucleation on Pt rod upper and lower rotation rates limits and an optimum rotation rate were distinguished for each cooling rate. Quality of the grown crystals by both techniques was characterized by optical transmission analysis.

Low-repetition rate femtosecond laser writing of optical waveguides in KTP crystals: analysis of anisotropic refractive index changes.

We report on the direct low-repetition rate femtosecond pulse laser microfabrication of optical waveguides in KTP crystals and the characterization of refractive index changes after the thermal annealing of the sample, with the focus on studying the potential for direct laser fabricating Mach-Zehnder optical modulators. We have fabricated square cladding waveguides by means of stacking damage tracks, and found that the refractive index decrease is large for vertically polarized light (c-axis; TM polarized) but rather weak for horizontally polarized light (a-axis; TE polarized), this leading to good near-infrared light confinement for TM modes but poor for TE modes. However, after performing a sample thermal annealing we have found that the thermal process enables a refractive index increment of around 1.5x10(-3) for TE polarized light, while maintaining the negative index change of around -1x10(-2) for TM polarized light. In order to evaluate the local refractive index changes we have followed a multistep procedure: We have first characterized the waveguide cross-sections by means of Raman micro-mapping to access the lattice micro-modifications and their spatial extent. Secondly we have modeled the waveguides following the modified region sizes obtained by micro-Raman with finite element method software to obtain a best match between the experimental propagation modes and the simulated ones. Furthermore we also report the fabrication of Mach-Zehnder structures and the evaluation of propagation losses.

Synthesis, crystal growth, thermal and spectroscopic studies of acentric materials constructed from aminopyridines and 4-nitrophenol

A series of single co-crystals of non-centrosymmetric complexes of different mono- and diaminopyridines, namely 4-aminopyridine, 3,4-diaminopyridine, 2-amino-6-methylpyridine, 2,6-diaminopyridine, 2-aminopyridine, with 4-nitrophenol were grown by slow evaporation technique from solution at constant temperature. Optical transparency in the region of 300–1100nm was found to be suitable for nonlinear optical applications with cut off wavelengths at 420–474nm for these co-crystals. Single crystal X-ray analysis confirms the non-centrosymmetric packing. Thermogravimetric and differential thermal analysis shows good thermal stability of the studied compounds with melting point at range 99–172°C for different co-crystals. The second harmonic generation efficiency has been measured on single crystals by comparative SHG technique relative to KTP crystal. The nonlinear optical coefficient of the compounds was found to be up to 39pm/V.

Thermally induced phase mismatching in a repetitively Gaussian pulsed pumping KTP crystal: a spatiotemporal treatment.

Thermally induced phase mismatching (TIPM) has been proven to be an influential issue in nonlinear phenomena. It occurs when refractive indices of crystal are changed due to temperature rise. In this work, the authors report on a modeling of spatiotemporal dependence of TIPM in a repetitively pulsed pumping KTP crystal. Gaussian profiles for both spatial and temporal dependences of pump beam were used to generate second-harmonic waves in a type II configuration. This modeling is of importance in predicting the nonlinear conversion efficiency of crystals when heat is loaded in the system. To this end, at first, an approach to solve the heat equation in a repetitively pulsed pumping system with consideration of the temperature dependence of thermal conductivity and realistic cooling mechanisms such as conduction, convection, and radiation, is presented. The TIPM is then calculated through the use of experimental thermal dispersion relations of KTP crystal. The results show how accumulative behaviors of temperature and TIPM (with its reverse sign) happen when the number of pulses is increased. Fluctuations accompanying temperature and TIPM were observed which were attributed to the off-time between successive pulses. Moreover, in this work, a numerical procedure for solving a repetitively pulsed pumped crystal is introduced. This procedure enables us to solve the problem with home-used computing machines.

Comparative study of intracavity KTP-based Raman generation between Nd:YAP and Nd:YAG lasers operating on the (4)F(3/2) → (4)I(13/2) transition.

Extending the spectral wavelengths of the diode-pumped Nd-doped lasers at 1.3 μm with the KTP crystal in the intracavity Raman configuration is reported for the first time to the best of our knowledge. A systematic comparison is performed to show that a better optical conversion efficiency for the Nd:YAP/KTP Raman laser could be achieved thanks to the higher peak power and linearly polarized radiation at 1341 nm, whereas up to four Stokes emission lines are generated from the Nd:YAG/KTP Raman laser as a result of the fundamental dual-color operation at 1319 and 1338 nm. The maximum Stokes output power of the developed Nd:YAP/KTP Raman laser reaches 1.04 W under an incident pump power of 16 W and a pulse repetition rate of 10 kHz, corresponding to the diode-to-Stokes conversion efficiency as high as 6.5%. The largest pulse energy and highest peak power are evaluated to be up to 104 μJ and 34.7 kW, respectively.

Low intensity noise and narrow line-width diode laser light at 540 nm

We present a convenient method to generate high quality single-frequency green light at a wavelength of 540 nm. It consists of a noise suppressed external cavity diode laser at a wavelength of 1080 nm by optical filtering and resonant optical feedback, and a frequency doubling of the fundamental light with an a-cut KTP crystal. Highly efficient conversion is realized by type II non-critical phase matching. A stable single-frequency operation with a maximum power of about 20 mW is performed for more than 3 h. Both the intensity noise and line-width reach the level of a monolithic nonplanar ring laser, which is well known for its extraordinarily narrow line-width and extremely low noise among available single-frequency operating lasers.

Complete anisotropic time-dependent heat equation in KTP crystal under repetitively pulsed Gaussian beams: a numerical approach.

In this work, a thorough and detailed solution for the time-dependent heat equation for a cylindrical nonlinear potassium titanyl phosphate (KTP) crystal under a repetitively pulsed pumping source is developed. The convection and radiation boundary conditions, which are usually ignored in the literature, have been taken into account, and their importance on the temperature distribution has been discussed in detail. Moreover, the temperature dependence of thermal conductivity of KTP was considered in the calculations, and its impact is discussed. It is shown that the radiation term has a negligible effect and can be dropped safely, while the temperature dependence of thermal conductivity is more influential, such that ignorance of it brings some errors into the modeling. The time evolution of the temperature while the crystal is pumping with a train of successive Gaussian pulses until reaching equilibrium is shown. To accomplish numerical calculations, we developed a homemade code written with the finite difference time domain method in Intel Fortran (ifort) and ran it with the Linux operating system.

GTR-KTP enhanced stable intracavity frequency doubled Cr,Nd:YAG self-Q-switched green laser

Stable, enhanced intracavity frequency doubled Cr,Nd:YAG self-Q-switched miniature green laser with gray tracking resistant KTP (GTR-KTP) crystal has been demonstrated at room temperature. The maximum average output power of 1.2 W at 532 nm was achieved at the absorbed pump power of 7 W, and the corresponding optical-to-optical efficiency was 17%. Laser pulses with a pulse energy of 16 µJ and peak power of 1.3 kW were achieved. The laser operated from 6.7 kHz to 75 kHz with the absorbed pump power. Near-diffraction-limited laser beam quality with M2 less than 1.5 was obtained. The stable laser operation was achieved with less than 3% fluctuation of the average output power within 2 h.

Compact Nd:YAlO$_{3}$/RbTiOPO $_{4}$ Based Intra-Cavity Optical Parametric Oscillator Emit at 1.65 and 3.13 μm

An intra-cavity optical parametric oscillator based on RbTiOPO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> (RTP) crystal simultaneous output eye-safe light and mid-infrared wavelength light was demonstrated. An laser diode end pumped acousto-optic Q-switched Nd:YAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> laser at 1.08 μm was used as the pump source. At an incident pump power of 8.7 W and a pulse repetition frequency of 20 kHz, total average output power up to 1.12 W (890 mW of signal light at 1.65 μm with and 230 mW of idler light at 3.13 μm) was obtained, with the diode to OPO total output conversion efficiency of 12.9%. The pulse width is about 4.5 ns and spectral linewidth is about 0.5 nm for the signal light. Compare to noncritical phase matching optical parametric oscillator using its isomorph KTP crystal, RTP crystal can extend signal wavelength up to 1.65 μm and absorb less idler wavelength.