Rb-doped KTP Research Articles

Properties of Rubidium-Doped Potassium Titanyl Phosphate (Rb: KTP) Grown by Hydrothermal Method

As an electro-optical crystal with excellent properties, potassium titanyl phosphate (KTP) has high conductivity limits electro-optical applications. In this experiment, Rb-doped KTP crystals were grown by the hydrothermal technique of micro-doping and sustained-release, the crystal structure was determined by XRD, the presence of Rb in the crystals was explored by EDS, and the role of Rb in the crystals was investigated by Raman technique. Frequency-dependent dielectric constants were studied at room temperature, which decreases sharply at low frequencies. The variation of the conductivity of the crystals at different temperatures was investigated, and it was found that the room temperature conductivity of the KTP crystals, which were micro-doping by large ionic, was able to drop to 10−13 S/cm, which is about two orders of magnitude lower than that of the pure KTP crystals.

Large-aperture periodically poled Rb-doped KTP with a short-period via coercive field engineering

We demonstrate periodic poling of large aperture Rb-doped KTP (RKTP) crystals with a QPM period of 3.43 µm via coercive field engineering. The periodically-poled RKTP has excellent pattern-fidelity, with a second harmonic generation (SHG) conversion efficiency of 1.4%/Wcm at 405 nm. We use ion-exchange (IE) to fabricate grating of high-and-low coercive fields and establish that the depth of the in-diffused Rb+ is the main parameter to achieve sufficiently large coercive field contrast that enables uniform periodic poling in the thick crystal. Furthermore, we demonstrate that our robust coercive field grating allows multiple cycles of polarization-switching which can be employed to decrease the refractive-index change along the polar axis, induced during the IE process.

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.

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. Multiple-pulse poling with triangular pulses was shown to have a detrimental effect on the QPM structure quality, while multiple square pulses can provide additional flexibility to the structuring process.

Intra-cavity frequency-doubled Yb:KYW laser using periodically poled Rb-doped KTP with a volume Bragg grating input coupler

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.

High-efficiency frequency converters with periodically-poled Rb-doped KTiOPO4

Periodic structuring of ferroelectric domains in 2mol% Rb-doped KTP is demonstrated using a room-temperature electric-field poling. Drastically reduced ionic conductivity in this material, or 2-orders of magnitude lower than in flux-grown KTP, makes it a good candidate for fabrication of quasi-phase-matched frequency converters. A coercive field of 3.4kV/mm has been measured at room temperature. The dispersion of the index of refraction and effective nonlinearity in quasi-phase-matched structures in Rb-doped KTP did not show significant difference from KTP. A normalized conversion efficiency of 2.5%W−1cm−1 for the frequency-doubling of 908.4nm has been obtained. A singly-resonant mid-infrared optical parametric oscillator with periodically-poled Rb-doped KTP generating 1.53μm signal and 3.49μm idler had threshold of 51MW/cm2 which is comparable to the best-quality periodically-poled KTP structures in the same optical cavity.

Near-Field Optical Spectroscopy: Enhancing the Light Budget

Abstract The near-field scanning optical microscope, or NSOM, provides spectroscopists with resolution beneath the diffraction limit. In the NSOM, an optical aperture smaller than the wavelength λ of the probe radiation is scanned in the near-field of a sample. Pixels are serially gathered and then constituted as a computer-generated image. Spectroscopic NSOM investigations demonstrating sub-λ, resolution include studies of photoluminescence, Raman spectroscopy, and single molecule fluorescence. Results of nano-Raman spectroscopy on semiconducting Rb-doped KTP are shown in figure 1. Figure la is a topographic image of the sample showing a square Rb-doped region in an otherwise undoped sample. Figure lc is a NSOM region of the corner of the doped region, and figure lb is an image of the same region taken within a Raman line. While these data do provide sub-λ spectroscopic resolution and other interesting features, the weak signal provided by current NSOM technologies and the low quantum efficiency of the Raman effect necessitated development of a very low-drift microscope and inconveniently long collection times.

Nano-Raman Spectroscopy and Imaging with a Near-Field Scanning Optical Microscope

Raman spectroscopy was performed using a near-field scanning optical microscope. This avoids the diffraction limit inherent in conventional optical microscopy techniques involving far-field optical components, and allows volumes significantly smaller than the cube of the wavelength to be investigated. The small sample volume coupled with the light-starved nature of the Raman effect itself makes such nano-Raman studies difficult. A near-field Raman microscope is described and results showing near-field effects in an investigation of Rb-doped KTP are presented. An image taken within a Raman feature demonstrates that nano-Raman imaging is indeed possible if the near-field instrument has considerable long-term stability, and that several unique aspects of the near-field data recommend this approach.

Nano-Raman Spectroscopy and Imaging with a NearField Scanning Optical Microscope

Raman spectroscopy was performed using a near-field scanning optical microscope. This avoids the diffraction limit inherent in conventional optical microscopy techniques involving far-field optical components, and allows volumes significantly smaller than the cube of the wavelength to be investigated. The small sample volume coupled with the light-starved nature of the Raman effect itself makes such nano-Raman studies difficult. A near-field Raman microscope is described and results showing near-field effects in an investigation of Rb-doped KTP are presented. An image taken within a Raman feature demonstrates that nano-Raman imaging is indeed possible if the near-field instrument has considerable long-term stability, and that several unique aspects of the near-field data recommend this approach.