There is a strong deviation from the usual 1/2 scaling of laser damage fluence for pulses below 10 ps in dielectric materials. This behavior is a result of the transition from a thermally dominated damage mechanism to one dominated by plasma formation on a time scale too short for significant energy transfer to the lattice. This new mechanism of damage ͑material removal͒ is accompanied by a qualitative change in the morphology of the interaction site and essentially no collateral damage. High precision machining of all dielectrics ͑oxides, fluorides, explosives, teeth, glasses, ceramics, SiC, etc.͒ with no thermal shock or distortion of the remaining material by this mechanism is described.

The azimuthal dependence of third-order and cascaded second-order nonlinear coupling are used to measure the relative contributions of each to direct third-harmonic generation in ␤-barium borate. This enabled the measurement of the values of 10(3) , 11 (3) , and 16(3) relative to the known ij (2) . Finally, conversion efficiencies to 3 of up to 6% from a single crystal were achieved with a femtosecond chirped-pulse-amplification laser with 200 GW/cm 2 in collimated beams.

Several nanosecond 0.53-μm laser pulses separated by several tens of nanoseconds have been shown to significantly enhance (three to ten times) material removal rates while minimizing redeposition and heat-affected zones. Economic, high-quality, high-aspect ratio holes (>10:1) in metals are produced as a result. A phenomenological model whereby the second laser pulse interacts with the ejecta produced by the first laser pulse and in close proximity to the material surface is consistent with the observations. Incident laser wavelengths of 1.05 and 0.35 μm also benefit from this pulse format.

Abstract. Three lidar receiver technologies using the total laser energy required to perform a set of imaging tasks are compared. The tasks are combinations of two collection types (3-D mapping from near and far), two scene types (foliated and unobscured), and three types of data products (geometry only, geometry plus 3-bit intensity, and geometry plus 6-bit intensity). The receiver technologies are based on Geiger mode avalanche photodiodes (GMAPD), linear mode avalanche photodiodes (LMAPD), and optical time-of-flight lidar, which combine rapid polarization rotation of the image and dual low-bandwidth cameras to generate a 3-D image. We choose scenarios to highlight the strengths and weaknesses of various lidars. We consider HgCdTe and InGaAs variations of LMAPD cameras. The InGaAs GMAPD and the HgCdTe LMAPD cameras required the least energy to 3-D map both scenarios for bare earth, with the GMAPD taking slightly less energy. We comment on the strengths and weaknesses of each receiver technology. Six bits of intensity gray levels requires substantial energy using all camera modalities.

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