A method of computing theoretical X-ray spectra in the range 30-150 kV is presented. The theoretical spectra are compared with constant potential, high resolution spectra from a tungsten target measured with a Ge(Li) detector, for a range of target angles, tube voltage and filtrations. Above 100 kV the spectra were also measured with a NaI detector but, as there was good agreement between the Ge(Li) and NaI detectors, only the former are presented. Spectra computed using Kramers' theory are also included for comparison, giving fairly good agreement at large target angles (30 degrees) but becoming gradually worse as the target angle decreased. Spectra may be computed by this method for any desired filtration, target angle, and tube voltage between 30 and 150 kV, in excellent agreement with the measured data.

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The semiconductor disk laser (SDL) is a versatile laser source offering multiwatt-level output powers and diffraction limited beams. While an approach to thermal management based on substrate removal has led to tens of watts of output power in the 1 m region, the use of intracavity diamond heatspreaders for thermal management has enabled multiwatt performance levels to be achieved at wavelengths from the red to the midinfrared. The modeling presented indicates that this dichotomy in approach arises from the ability of the heatspreader approach to bypass the thermal resistance of the mirror structure built into the SDL. The power scaling limitations of SDLs with heatspreaders are explored: nonaxial heat flow in the heatspreader is shown to limit the power scaling with pump spot radius. The critical roles of the pump spot size and output coupling on efficiency are experimentally investigated. An output power of 7 W in a 1060 nm SDL is achieved with the maximum output power achieved at a pump spot radius of 85 m

High-resolution absorption and stimulated-emission cross-section spectra are presented for monoclinic Nd:KGd(WO4)2 (Nd:KGW) laser crystals in the temperature range 77-450 K. At room-temperature, the maximum stimulated emission cross-section is σSE =21.4×10 -20 cm 2 at 1067.3 nm, for light polarization E || Nm. The lifetime of the 4 F3/2 state of Nd 3+ in KGW is practically temperature independent at 115±5 µs. Measurement of the energy transfer upconversion parameter for a 3 at.% Nd:KGW crystal proved that this was significantly smaller than for alternative hosts, ~2.5×10 -17 cm 3 /s. When cut along the Ng optical indicatrix axis, the Nd:KGW crystal was configured as a microchip laser, generating ~4 W of continuous-wave output at 1067 nm with a slope efficiency of 61% under diodepumping. Using a highly-doped (10 at.%) Nd:KGW crystal, the slope efficiency reached 71% and 74% when pumped with a laser diode and a Ti:Sapphire laser, respectively. The concept of an ultrathin (250 µm) Nd:KGW microchip laser sandwiched between two synthetic diamond heat-spreaders is demonstrated.

Polyvinylpyrrolidone (PVP) can be used to produce upconversion nanoparticles (UCNPs) in an advantageous manner, i.e. at modest temperatures in open-to-air conditions with simple hotplate and flask apparatus. However, the influence of PVP parameters on the formation of UCNPs has not been previously investigated. In this exploratory study, we establish that PVP molecular weight and relative amount of PVP can greatly influence the morphology and diameter of NaYF4:Yb,Er UCNPs produced via the PVP-assisted route. At nominal amounts of PVP, varying the molecular weight of PVP in synthesis between 10,000 g/mol (PVP10), 40,000 g/mol (PVP40), and 55,000 g/mol (PVP55), had minimal effect on UCNP morphology, whereas reducing the quantity of PVP10 and PVP40 in the reaction to 10% of the nominal amount resulted in two notable effects: (1) the generation of a greater range of UCNP diameters and (2) the production of an unexpected sub-population of rhombus-shaped UCNPs. Bulk and individual nanoparticle analysis indicates that all UCNP morphologies were cubic (α-phase) crystal structure and consisted of NaYF4:Yb,Er. Optical emission properties exhibited only modest green and red luminescence emission ratio when PVP parameters were varied. However, separately produced PVP40 NaYF4:Yb,Tm UCNPs exhibited a much more intense and dual-band blue /red emission. This exploratory work demonstrates that tailoring PVP content in synthesis of UCNPs can greatly alter morphology of UCNPs produced and should be carefully considered in experimental design. However, the underlying mechanisms of action of the role PVP plays in this synthesis remain unclear. Ultimately, significant further work is still required to fully elucidate the relevant chemistry to achieve full control of PVP-UCNP synthesis.