An Electro-Optic, Actively Q-Switched Tm:YAP/KGW External-Cavity Raman Laser at 2273 nm and 2344 nm

This paper presents a KGW Raman laser with an external-cavity configuration in the 2 μm region. The Raman laser is pumped by unique, electro-optic, actively Q-switched Tm:Yap laser, emitting at 1935 nm. The electro-optic modulation is based on a KLTN crystal, enabling the use of a short crystal length, with a relatively low driving voltage. Due to the KGW bi-axial properties, the Raman laser is able to lase separately at two different output wavelengths, 2273 and 2344 nm. The output energies and pulse durations for these two lines are 0.42 mJ/pulse at 18.2 ns, and 0.416 mJ/pulse at 14.7 ns, respectively. This is the first implementation of a KGW crystal pumped by an electro-optic active Q-switched Tm:Yap laser in the SWIR spectral range.

A systematic study of PPLN length dependence in intracavity SHG

In this paper, a systematic study of the relationship between nonlinear crystal length and intracavity second-harmonic generation (SHG) using MgO-doped periodically-poled lithium niobate (MgO:PPLN) is presented. The experimental results demonstrate a relationship between the maximum SHG power generated and the full-width at half maximum (FWHM) of the crystal’s temperature tuning curve to the length of the nonlinear optical crystal. It was shown that maximum SHG power increases rapidly with the increase of MgO:PPLN length, reaching a saturation length (~ 2 mm), which is much shorter than that predicted by the single-pass SHG theory. This saturation length of the MgO:PPLN crystal is almost independent on 808 nm pump power for typical powers used in continuous wave intracavity SHG lasers. In addition to this saturation effect, a broadening effect was also observed, the FWHM of the temperature tuning curve was shown to have a larger FWHM than that predicted by the single-pass SHG theory for MgO:PPLN shorter than the saturation length. This work has the benefit of allowing engineers to optimize nonlinear crystal length when developing intracavity SHG based diode-pumped solid state (DPSS) lasers.

A Systematic Study of PPLN Length Dependence in Intracavity SHG

In this paper, a systematic study of the relationship between nonlinear crystal length and intracavity second-harmonic generation (SHG) using MgO-doped periodically-poled lithium niobate (MgO:PPLN) is presented. The experimental results demonstrate a relationship between the maximum SHG power generated and the full-width at half maximum (FWHM) of the crystal’s temperature tuning curve to the length of the nonlinear optical crystal. It was shown that maximum SHG power increases rapidly with the increase of MgO:PPLN length, reaching a saturation length (~2 mm), which is much shorter than that predicted by the single-pass SHG theory. This saturation length of the MgO:PPLN crystal is almost independent on 808 nm pump power for typical powers used in continuous wave intracavity SHG lasers. In addition to this saturation effect, a broadening effect was also observed, the FWHM of the temperature tuning curve was shown to have a larger FWHM than that predicted by the single-pass SHG theory for MgO:PPLN shorter than the saturation length. This work has the benefit of allowing engineers to optimize nonlinear crystal length when developing intracavity SHG based diode-pumped solid state (DPSS) lasers.

Microcrystal alignment in drawn fiber over sub-meter to kilometer length scales

This paper describes a method for aligning stiff, high-aspect-ratio microcrystals over macro-length scales using a polymer fiber drawing process. A composite preform was constructed with an interfacial, liquid shell layer of grapeseed oil suspending ytterbium-doped potassium lutetium fluoride microcrystals (30% Yb:K2LuF5, KLF) between adjacent cylindrical surfaces of acrylic (polymethyl methacrylate, PMMA). The mean length of synthesized KLF microcrystals was 67 microns, and the mean aspect ratio, equivalent to crystal length divided by diameter, was eight. The acrylic-host preform was drawn into fiber, resulting in uniform reduction of all cross-sectional dimensions by a factor of approximately 20 in the final fiber. A corresponding width reduction of the interstitial liquid-filled gap, containing microcrystals between the polymer surfaces, constrains the microcrystals and causes alignment of the crystal long axes parallel to the axis of the drawn composite fiber. Alignment was best for clearly separated microcrystals and improved even further with the longest lengths, or highest aspect-ratio microcrystals.

Investigation of the Light Yield Distribution in LYSO Crystals by the Optical Spectroscopy Method for the Electromagnetic Calorimeters of the COMET Experiment

The distribution of the light yield and luminescence intensity along LYSO:Ce crystal length is investigated. These distributions, determined by different defects and emission centers of the dopant in the crystalline structure and its distribution along the length, is measured by two methods: the gamma spectroscopy using radiation sources and the optical spectroscopy using ultraviolet sources. It is shown that crystals have considerable variation of the light yield and luminescence intensity both over the length of an individual crystal (in the growing direction) and for different crystals. It is established that the correction factors for the segmented calorimeter of the COMET experiment can be obtained using optical spectroscopy methods. Consideration of the correction factors will significantly reduce an error of energy measurement in a segmented calorimeter during data handling.

Texture constraints on crystal size distribution methodology: An application to the Laki fissure eruption

Modeling crystal size distributions often requires the extraction of 2D discrete crystal lengths to calculate 3D volumetric equivalences. These apparent lengths are obtained from digital images that exploit different physical and chemical characteristics of samples, and the choice of image type can affect the interpretation of crystal length measurements, thus affecting crystal size distribution modeling. To examine method- and texture-based effects on extracting crystal size distributions, we obtained plagioclase length measurements from two texturally opposing basaltic lava samples from the well-documented Laki fissure eruptions of 1783–1784. Using approaches that consider inherent texture-based limitations of 2D image types, we employed manual tracing and imaging software to extract plagioclase crystal lengths from three types of images: (1) photomicrographs from polarized-light microscopy, (2) backscatter electron images from scanning electron microscopy, and (3) energy-dispersive X-ray maps from automated mineralogy. Our results demonstrate that (1) phenocrysts (L ≥ 150 μm) and groundmass plagioclase (L < 150 μm) in our basalt samples appear with multiple aspect ratios, while the latter also display greater nucleation densities as crystal size population are continuously refined over increasingly smaller crystal lengths; (2) complex crystal clusters must be manually dissected into their discrete crystal components to produce meaningful crystal size distributions; (3) localized electron backscatter diffraction analysis reveals mild preferred orientation in complex clusters and groundmass, the latter confirmed by variations in crystal size distributions between orthogonal backscatter electron images; and (4) method-induced variations in both aspect ratio and crystal length determination can produce a wide range of kinetic interpretations that pose challenges for cross-research comparisons. For phenocrysts, compensating for clustering and fracturing through manual tracing remains the most effective method, while groundmass populations can be addressed with high-resolution (micrometer-scale) automated scanning electron microscopy for deciphering late-stage eruptive behavior. A texture-focused protocol should be established, as any kinetic information derived from crystal size distribution analyses across multiple studies employing multiple approaches cannot otherwise be directly compared.

Skull Melting Growth and Characterization of (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 Crystals

(ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals have been grown by directional melt crystallization in a cold crucible. The chemical and phase compositions of the crystals have been characterized using energy dispersion X-ray spectroscopy (EDX), Raman scattering spectroscopy and transmission electron microscopy (TEM). The X-ray photoelectron emission method has been used for determining the valence state of the Ce ions. We show that directional melt crystallization produces an inhomogeneous ceria distribution along the crystal length. The as-grown crystals are mixtures of cubic and rhombohedral zirconia modifications. The rhombohedral phase has an inhomogeneous distribution along crystal length. Melt crystallization does not produce single-phase cubic (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals. The formation of the phase structure in the crystals for different synthesis methods has been discussed.

Каскадная генерация второй гармоники с половинным порядком периодической ориентации

We theoretically demonstrate cascaded fourth and second harmonic generation in a periodically-poled nonlinear crystal with a half-order of phase-matching period. We consider a cascaded process in which four photons of the fundamental harmonic firstly convert into an intermediate photon of the fourth harmonic, which parametrically decays into two photons of the second harmonic at the second stage. Phase-matching for this cascaded nonlinear conversion is provided by using an asymmetric periodical poling. We use the quantum spatial Heisenberg equations to describe light propagation and conversion inside the nonlinear crystal. With this approach, we calculate second and fourth harmonic average number of photons as a function of the nonlinear crystal length.