Low-threshold diode-laser-pumped OPOs based on QPM materials
Although attractive as compact sources of tunable infrared radiation, optical parametric oscillators pumped directly by single-mode diode lasers require extremely low thresholds. This talk will discuss the realisation of such low-threshold devices using QPM materials.
Continuous-wave pump-enhanced singly resonant optical parametric oscillator pumped by an extended-cavity diode laser
A continuous-wave pump-enhanced singly resonant optical parametric oscillator (OPO) directly pumped by a grating-stabilized external-cavity diode laser operating at ≈810 nm is described. The OPO was based on periodically poled LiNbO3 and could be tuned over 1.06–1.19 μm at the signal and 2.58–3.44 μm at the idler. The OPO threshold was typically 25–30 mW over the observed tuning range. Up to 4 mW of one-directional idler output was obtained for 62 mW of external-cavity diode laser pump power. The high stability of the external-cavity diode-laser pump source allowed locked, single-mode OPO operation for periods of greater than 1 h.
Characterization of a tube-in-shell thermosyphon heat exchanger for solar water heating
Performance of a double-wall, natural convection, two-pass, tube-in-shell heat exchanger designed for use in a solar water heating system is measured. The heat exchanger is mounted along the length of a solar water storage tank. Flow of cold water on the shell side of the heat exchanger is driven solely by buoyancy forces. Hot side fluid is pumped. Flow rate, pressure drop and temperature data needed for a semi-empirical model of the heat exchanger are obtained. Performance is measured for forced convection, hot side volumetric flow rates of 0.016, 0.032 and 0.079 l/s. Temperature difference between hot and cold fluid at the inlets is varied from 0 to 75 degC. Measured values include thermosyphon and forced flow rates, temperature differences across the beat exchanger, vertical temperature distribution in the storage tank, and pressure drop due to shear on the thermosyphon side of the heat exchanger. Heat exchanger effectiveness and overall heat transfer area product (UA) are calculated. Thermosyphon mass flow rates are on the order of 0.01 kg/s. Although the low flow rates create thermal stratification of the water storage tank, they restrict energy transfer in the heat exchanger.