RbTiOPO4 Research Articles

Growth and characterization of rubidium titanyl phosphate thin films by pulsed laser deposition

The mm2 orthorhombic potassium titanyl phosphate crystal, i.e. KTiOPO4 (KTP), is a famous biaxial nonlinear optical crystal widely used commercially for second harmonic generation (SHG) or optical parametric oscillation (OPO) pumped by a 1.064 μm Nd:YAG laser for example. Most of its applications are based on bulk single KTP crystals. However, there is a strong interest to elaborate submicrometric waveguides in the framework of integrated photonic device. Such waveguides could be a serious alternative to efficient low energy nonlinear optical devices in particular for Telecom or spectroscopic applications.PLD is a technique particularly well suited for growing single oxides films with complex chemical composition. This technique consists in a high energy laser ablation of a material with the same chemical composition than that of the desired layer. The plasma of the ablated material is then condensed on the substrate and heated to a temperature such as the aggregates can self-organize on the atomic lattice of the substrate leading to the epitaxial layer.In this study, we performed epitaxial growth of the RbTiOPO4 (RTP) phase on KTP single crystals by PLD. The target that has been used was a single RTP crystal. However, by chemical analysis and XRay diffraction we demonstrated that due to alkali interdiffusion between film and substrate, it was not possible to achieve a pure layer of RTP but most likely an mixed stoichiometry KxRb(1-x) TiOPO4 but still in epitaxy.

Enhancements of Second Harmonic Generation and Birefringence in Traditional RbTiOPO4‐Type Crystals by Aliovalent Substitution of Ti Site

AbstractStrong second harmonic response and large birefringence of nonlinear optical (NLO) materials have important scientific and technical significance for tunable lasers. The second harmonic generation (SHG) response in NLO crystals has been generally enhanced by improving the polarization of bridged oxygen atoms or local structural distortions, while the synergy of the two contributions to enhance the SHG response is rarely explored. To this end, new crystals with traditional RbTiOPO4 (RTP)‐structure, Rb1–xTi1–xSbxOPO4 (x = 0.01, 0.03, and 0.06), containing novel functional SbO6 octahedra and Rb vacancies are designed through a one‐site aliovalent substitution and grown in this work. Rb0.94Ti0.94Sb0.06OPO4 exhibits an enhanced SHG response, nearly 1.48 times that of the RTP crystal, accompanied by the largest birefringence in phosphates (exp. 0.202 at 546 nm, cal. 0.156 at 1064 nm). Theoretical calculations and crystal structure analysis confirm that the higher polarizability of bridged oxygen and the local structural distortions in Rb1–xTi1–xSbxOPO4 strengthen the NLO activity of neighboring units, thus significantly prompt the SHG effect and optical anisotropy. This study provides a new paradigm to deeply improve the NLO performance of crystal materials and benefits for expanding their practical applications.

Self‐Frequency‐Mixing Raman Laser Based on RbTiOPO4

AbstractIn this work, the generation of yellow laser emission from a self‐frequency‐mixing Raman laser utilizing RbTiOPO4 (RTP) is reported. The RTP crystal is positioned within the cavity of a Nd:YAG/Cr4+:YAG composite, passively Q‐switched laser. By utilizing this intracavity configuration, Raman conversion of the fundamental laser wavelength to Stokes wavelengths and frequency mixing of these near‐infrared wavelengths to the visible wavelength range is achieved using a single RTP crystal. Multiple visible wavelengths are generated, with a primary line at 574.3 nm and additional weaker lines at 552.3 and 563.9 nm. An average output power of 180 mW is measured from the output coupler end of the laser setup (note that laser emission in the visible wavelength range is also generated toward the input end of the laser cavity) for an incident pump power of 11.4 W. The results demonstrate the potential of RTP as a self‐frequency‐mixing, Raman crystal, which may be used for the development of efficient and compact yellow lasers.

Pulse peaks synchronize dual-wavelength laser based on Q-switch delay trigger

In this paper, an all-solid-state Nd:YVO4 laser with peak synchronize output of 1064/1342 nm dual-wavelength Q-switched pulse is designed. Double-cavity structure with single Nd:YVO4 crystal and double RbTiOPO4 (RTP) electro-optic (EO) Q-switch is built. At repetition frequency of 10 kHz, taking the trigger time of EO Q-switch at 1342 nm as reference, at the delay time of EO Q-switch at 1064 nm as 1.3 μs, the pulse peak synchronize dual-wavelength laser is obtained, and the pulse power is 1.63 W and 1.63 W with the width is 55.64 ns and 105.2 ns respectively.The beam quality is Mx2=1.61,Mx2=1.64 and Mx2=1.43,My2=1.54, respectively.

1064/1342 nm dual-wavelength double electro-optical Q-switched Nd:YVO4 laser

An all-solid-state Nd:YVO4 laser producing dual-wavelength of 1064/1342 nm was designed, which took a plan of double RTP (RbTiOPO4) electro-optic Q-switch of 1064 nm and 1342 nm, by controlling the voltage of double RTP crystals to control the output laser power ratio of dual-wavelength. When the repetition rate is 10 kHz, the 1064/1342 nm dual wavelength laser output with 1.6/1.6 W, power ratio of 1:1, and basically overlapping pulse peak time is obtained by changing the crystal voltage.

Electro-optic Q-switched dual-wavelength coaxial alternating output laser at 1064 and 1319 nm

In this study, by combining the voltage-increased and voltage-decreased electro-optic (EO) Q-switched technologies, a dual-wavelength coaxial alternating output solid-state laser operating at 1064 and 1319 nm is demonstrated. Two wavelengths are generated from different gain medias, and combined together with a shared EO Q-switcher which is accomplished by using a double-crystal RbTiOPO4 (RTP). The coaxial alternating 1064 nm and 1319 nm Q-switch pulses with 200 μs delay are obtained. This produces a maximum output energy of 38.96 mJ with a pulse width of 15.7 ns for the 1319 nm component, and a maximum output energy of 38.73 mJ with a pulse width of 14.7 ns for the 1064 nm component at a pulse repetition frequency (PRF) of 10 Hz when the pumping current are 90 A and 70 A, respectively.

Efficient Kerr nonlinearity in RTP induced by electro-optically adjustable cascaded second-order process

This paper reveals an analytical perception of electro-optically tunable cascaded Kerr-lens using RbTiOPO4 (RTP) crystal where the advantageous properties of the crystal have been studied to mitigate the limitations of KTiOPO4 (KTP) and BaB2O4 (BBO) in intracavity high power laser generation. An external electric field application to the z-direction of RTP is introducing a phase mismatch condition leading to a nonlinear phase shift within propagating optical waves. Based on simulated endeavors, a maximum effective nonlinear refractive index of ±1.4053 × 10−13 cm2/W is calculated by developing a phase shift of ∓4.6 rad. In contrast, KTP and RTP both have almost similar optical properties but due to certain special features like higher damage threshold, less walk-off angle etc., RTP is firmly accepted for high power applications. Additionally, this article is augmented to analyze the self-focusing and defocusing phenomenon owing to the non-uniform distribution of radial intensity of the propagating Gaussian beam. To the best of author's knowledge, the present analysis manifests the superior performance of RTP that may pave the way to devise a configurable lens analogous to Kerr-lens having an electro-optically tunable focal length.

Laser-diode dual-end-pumped electro-optic Q-switched slab Tm:YAP laser

A high-repetition-rate and double-end pumped electro-optic Q-switched Tm:YAlO3 (Tm:YAP) laser is reported. The Tm:YAP slab crystal cut by c-axis is used as the laser gain medium, and the RbTiOPO4(RTP) crystal is selected as the electro-optic Q-switched crystal. Choosing volume Bragg gratings (VBG) as the input mirror to narrow the output line width. When the pump power is 79.2 W, at a repetition rate of 10 kHz, maximum average-output-power of 21.96 W is achieved, with the pulse width of 20.64 ns and output energy of 2.20 mJ. The output peak power is 107.3 kW and the slope efficiency is 29.2%. The center wavelength is 1937.87 nm and the line width is 0.73 nm. The beam quality in the x direction is 1.48, and in the y direction is 1.50.

A 1-kHz Single Frequency Nd:YAG Ring Laser by Injection Seeding**Supported by the National Key Research and Development Program of China under Grant No 2017YFB1104500, and the National Natural Science Foundation of China under Grant No 61875100.

We report on an injection seeded 1 kHz single frequency pulsed Nd:YAG ring laser with pulse energy of 5.2 mJ and pulse width of 9.9 ns. The ramp-fire technique is used to maintain single frequency operation and the cavity length is modulated by an intracavity RbTiOPO4 (RTP) crystal. The frequency stability (rms) of the output pulse is 1.99 MHz over 1 min and the linewidth is 64 MHz.

Frequency stabilization of an injection seeded Nd:YAG ring oscillator by ramp-fire technique with a RbTiOPO4 modulator

We report on an injection seeded Q-switched Nd:YAG zigzag slab ring oscillator with pulse energy of 67 mJ and pulse duration of 19 ns at repetition rate of 20 Hz. With a RbTiOPO4 (RTP) electro-optic crystal as the intra-cavity phase modulator, stable single frequency operation is achieved using the ramp-fire technique with a 10 µs linear voltage ramp sweeping 2.5 free spectral ranges. Frequency jitter of output pulse at 1064 nm is measured to be 2.0 MHz over 7 min. The beam quality factor is $$ M_{x}^{2} = 1.38 \pm 0.03, M_{y}^{2} = 1.29 \pm 0.02 $$ in seeded operation, which is improved from that of $$ M_{x}^{2} = 1.67 \pm 0.01, M_{y}^{2} = 1.35 \pm 0.01 $$ in free oscillation. The measured linewidth of the output is 27 MHz, which is 1.2 times Fourier-transformed-limited. Based on the RTP crystal as the modulator, the ramp-fire technique with a high ramp speed is capable of achieving high frequency and timing stability.

Development of an injection-seeded single-frequency laser by using the phase modulated technique**Project supported by the National Key Research and Development Program of China (Grant Nos. 2017YFB1104500 and 2016YFB0701000).

An injection-seeded single-frequency Q-switched Nd:YAG laser is accomplished by using a phase modulated ramp-fire technique. A RbTiOPO4 (RTP) electro-optic crystal is selected for effective optical path length modulation of the slave self-filtering unstable resonator. This single-frequency laser is capable of producing 50 mJ pulse energy at 1 Hz repetition rate with a pulse width of 16 ns. The standard deviation of laser pulse intensity for consecutive 100 shots from the mean pulse intensity is less than 1.05%. A spectral linewidth of less than 0.5 pm with a frequency jitter of about 14 fm over 30 min is obtained.

14 GHz broadband and continuously frequency-tuned Nd:YVO4 laser with an RTP etalon.

A laser-diode-pumped broadband and continuously frequency-tuned all-solid-state Nd:YVO4 laser at 1064nm with an output power of 200mW is demonstrated. A RbTiOPO4 (RTP) etalon and a piezoelectric-transducer (PZT) are utilized for coarse and fine frequency tuning, respectively. Dependence of the frequency excursion on the applied voltage to the RTP etalon and the displacement of the PZT is theoretically and experimentally investigated. A continuous frequency tuning of 14GHz is conducted by synchronous adjustment of the RTP etalon and the PZT. The tuning covers more than 6 times the longitudinal mode spacing of a laser resonator without any mode hops.

Terahertz parametric oscillator with the surface-emitted configuration in RbTiOPO4 crystal

Terahertz parametric oscillator based on RbTiOPO4 (RTP) crystal utilizing the surface-emitted configuration under high pumping pulse energy and low pulse repetition rate is investigated. The obtained THz wave was discontinuously tuned from 3.01 to 3.09 THz, from 3.53 to 4.17 THz, from 4.54 to 4.66 THz, and from 5.35 to 5.89 THz, respectively. The maximum output THz wave pulse energy was 1.77 μJ at 3.85 THz. It was obtained when the pumping pulse energy was 120 mJ and the pumping beam diameter was 3.0 mm. The polarization of THz wave was along the z axis of the RTP crystal. The THz beam on its output surface was approximately elliptical with a major axis of 6.5 mm and a minor axis of 3.5 mm. The divergence angles were 2.45° in the horizontal direction, and 3.88° in the vertical direction.

Ab-initio investigation of Rb substitution in KTP single crystal

The effects of rubidium doping on the structural, electronic, and optical properties of KTiOPO4 (KTP) are investigated in the framework of density functional theory. The equilibrium structural parameters of KTP and RbTiOPO4 (RTP) are calculated within the local density and Perdew-Burke-Ernzerhof (PBE), Wu-Cohen, and PBEsol formulation of generalized gradient approximations. We discuss that PBEsol predicts better equilibrium parameters for the KTP alloy. In addition, the variation of lattice constants and Ti-O-Ti bond angles are evaluated as a function of rubidium concentration. The modern modified Becke-Johnson functional is applied for more accurate band gap determination in the pure and alloyed KTP/RTP compounds. The phenomenological pseudoinversion parameter is calculated for a qualitative understanding of the effect of impurity on a non-linear optical response of KTP. We also analyze the behavior of the dielectric function, dispersive refractive indices, and birefringence of KTP/RTP alloys.

Crystal growth, electronic structure and luminescence properties of Nb/Yb co-doped RbTiOPO4 crystals

Nb/Yb co-doped RbTiOPO4 (RTP) crystals were successfully grown by a top-seeded solution growth method from two different kinds of flux systems. 5%Nb/3%Yb: RTP crystal with more transparency was obtained from the mixed solvent containing MoO3. The chemical composition was analyzed by Electron Probe Microanalyzer (EPMA), and the result indicated that co-doping of Nb and Yb into RTP can greatly increase the concentration of Yb in RTP crystal. The addition of MoO3 into self-flux system can improve the quality of as-grown crystals, but it is not helpful to introduce Yb into crystal. The electronic structures of Nb/Yb: RTP crystals were analyzed using X-ray photoelectron spectra (XPS). The results show that the binding energy difference between O 1s and P 2p levels (ΔBE (O-P)) increases firstly with the increase of Yb content, and then decreases with Nb content increasing, which is associated with the covalency change of O-P bonds in crystals. However, the doping has little influence on the chemical bond properties of O-Ti. The FL spectra of Nb/Yb: RbTiOPO4 crystals were also analyzed, and five emission peaks characteristic of Yb3+ ions were observed.

Modification of RbTiOPO4 (001) crystal surface induced by Ar+ ion bombardment: X-ray photoelectron spectroscopy and first-principles studies

The (001) crystal surface of RbTiOPO4 (RTP) were bombarded by Ar+ ion during different times (2–20 min) and the resulting chemical modification on surface has been studied by X-ray photoelectron spectroscopy (XPS) and first-principles calculations. Ion bombardment can lead to great structural modification on the surface of RTP crystal. Reduction of Ti4+ ions to the lower valence state (Ti3+) and formation of oxygen vacancies occur with Ar+ ion irradiation. With the increase of irradiation time, proportion of reduced Ti3+ ions and number of oxygen vacancies increase accordingly. Fraction of oxygen in P-O-Ti bonds decreases with increasing oxygen vacancies after bombardment for 5–20 min. We think that oxygen vacancies come from breaking of P-O-Ti bonds. The results were also confirmed theoretically by first-principles calculations. Existence of oxygen vacancies is also confirmed by absorption spectra. Formation of Ti3+ state can be ascribed to the loss of surrounding oxygen caused by Ar+ ion irradiation. This work helps us to better understand the ion-beam interaction with RTP surfaces.

24 THz/s continuously linearly frequency-modulated Nd:YVO_4 laser

We demonstrate a linearly frequency-modulated laser from a laser diode (LD) pumped Nd:YVO4 laser. A fast frequency tuning of 2.40 THz/s with a tuning range of 6 GHz is achieved in LD pumped Nd:YVO4 1064 nm laser by using RbTiOPO4 (RTP) crystals as the frequency modulator. The continuous tuning range is more than 3 times the longitudinal mode spacing of the resonator. The maximum output power of frequency-modulated laser reaches 160 mW at 1064 nm. Linewidth of the single frequency laser is measured to be 190 kHz by a delay self-heterodyne interferometer. A deviation lower than 60 MHz is obtained during linear modulation.

Numerical Investigation of Photon-Pair Generation in Periodically PoledMTiOXO4(M=K, Rb, Cs;X=P, As)

We present a detailed numerical investigation of five nonlinear materials and their properties regarding photon-pair creation using parametric downconversion. Periodic poling of ferroelectric nonlinear materials is a convenient way to generate collinearly propagating photon pairs. Most applications and experiments use the well-known potassium titanyl phosphate (KTiOPO4, ppKTP) and lithium niobate (LiNbO3, ppLN) crystals for this purpose. In this article we provide a profound discussion on the family of KTP-isomorphic nonlinear materials, including KTP itself but also the much less common CTA (CsTiOAsO4), KTA (KTiOAsO4), RTA (RbTiOAsO4) and RTP (RbTiOPO4). We discuss in which way these crystals can be used for creation of spectrally pure downconversion states and generation of crystal-intrinsic polarisation- and frequency entanglement. The investigation of the new materials disclosed a whole new range of promising experimental setups, in some cases even outperforming the established materials ppLN and ppKTP.

RbTiOPO4 cascaded Raman operation with multiple Raman frequency shifts derived by Q-switched Nd:YAlO3 laser.

An intra-cavity RbTiOPO4 (RTP) cascade Raman laser was demonstrated for efficient multi-order Stokes emission. An acousto-optic Q-switched Nd:YAlO3 laser at 1.08 μm was used as the pump source and a 20-mm-long x-cut RTP crystal was used as the Raman medium to meet the X(Z,Z)X Raman configuration. Multi-order Stokes with multiple Raman shifts (~271, ~559 and ~687 cm−1) were achieved in the output. Under an incident pump power of 9.5 W, a total average output power of 580 mW with a pulse repetition frequency of 10 kHz was obtained. The optical conversion efficiency is 6.1%. The results show that the RTP crystal can enrich laser spectral lines and generate high order Stokes light.

Short pulse diode-pumped Tm:YAG slab laser electro-optically Q-switched by RbTiOPO4 crystal

In this paper, a laser diode end pumped RbTiOPO4 (RTP) electro-optically Q-switched Tm:YAG slab laser was demonstrated. Stable Q-switched pulse with the shortest pulse width of 58 ns and an average output power of 7.5 W were realized at the repetition rate of 1 KHz, corresponding to the slope efficiency of 21.7%.