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Degenerate pump-probe spectroscopy was used for the measurement of femtosecond resonant nonlinear refraction in Nd:YVO4.

Abstract: In the formation of liquid drops, different kinds of liquids may have different outer profiles; the change of volume and shape in the process of drop formation can indirectly reflect liquid''s physical and chemical properties, such as surface tension and viscosity, etc. Real-time detection the size of drops in the forming process is on the basis of drop analysis technique. Previous researchers have studied that optic fiber and capacitance drop sensor fusion technology can indirectly gain drop''s form and the volume. This article is based on the optic fiber and capacitance drop sensor theory, designing the system based on the LabVIEW software to realize the LDF (Liquid Drop Fingerprint) data acquisition function. The experiment results show that the system can well realize the acquisition, compared with the traditional VC programming technology, this data acquisition system is high efficiency. [Copyright &y& Elsevier]

To achieve the aim of precise measurement of a target micro-sphere, approximately 0.2 mm in diameter, a laser confocal probe was designed. To improve the output signal, a mathematical model of the photoelectric signal was proposed. The diameter of the pinhole was determined, and the optical path was adjusted; the oscillating units were designed. The performance of the probe was validated by experiments using gauge blocks combined with a micro-motion measuring mount model. Besides, a more accurate signal processing method was suggested. [ABSTRACT FROM AUTHOR]

Picosecond carrier dynamics of deep bandtail states (3.1 eV) in an unintentionallyn-doped GaN epilayer at room temperature under high excitation densities (i.e.,N0 = 1.0× 1019- 1.1× 1020 cm-3) have been investigated with nondegenerate femtosecond pump-probe (267/400 nm) reflectance (?R/R0). All ?R/R0 traces possess a ~2 ps buildup time that represents an overall time for the initial non-thermal carrier population to relax towards the continuum extremes and then into the probed tail states. We observe a saturation of ?R/R0 initial (first 10 ps) recovery rate ?i at a density of 5- 6×1019 cm-3 close to the Mott transition threshold obtained from time-integrated PL measurements. Such a saturation phenomenon has been identified as the trap-bottleneck due to the bandtail states and deep traps. AsN0 is further increased, ?i accelerates due to the onset of Auger recombination as the trap-bottleneck becomes effective. The best fit by the Auger model forN0 in the range of the mid-1019-1020 cm-3 yields an Auger coefficient ofCa~ 5.0× 10-30 cm6 s-1. [ABSTRACT FROM AUTHOR]