Multiple single unit recording in the cortex of monkeys using independently moveable microelectrodes.

Simultaneous recording from multiple single neurones presents many technical difficulties. However, obtaining such data has many advantages, which make it highly worthwhile to overcome the technical problems. This report describes methods which we have developed to permit recordings in awake behaving monkeys using the 'Eckhorn' 16 electrode microdrive. Structural magnetic resonance images are collected to guide electrode placement. Head fixation is achieved using a specially designed headpiece, modified for the multiple electrode approach, and access to the cortex is provided via a novel recording chamber. Growth of scar tissue over the exposed dura mater is reduced using an anti-mitotic compound. Control of the microdrive is achieved by a computerised system which permits several experimenters to move different electrodes simultaneously, considerably reducing the load on an individual operator. Neurones are identified as pyramidal tract neurones by antidromic stimulation through chronically implanted electrodes; stimulus control is integrated into the computerised system. Finally, analysis of multiple single unit recordings requires accurate methods to correct for non-stationarity in unit firing. A novel technique for such correction is discussed.

Tapered bow-tie lasers for high energy Q-switched pulse generation

A new kind of Q switched laser, the bow tie laser is introduced. This type of laser permits large area facets at both ends so that generation of high optical powers involve low optical intensities to prevent optical damage. The incorporation of doubled tapered waveguide structure to the Q switched multicontact laser has increased the optical pulse energies and peak powers of the laser.

High-power and picosecond pulse generation from a passively Q-switched tapered InGaAs/GaAs laser

Tapered waveguides have been used for enhancing pulse powers in Q-switched AlGaAs and InGaAsP lasers. This paper reports on passively Q-switched pulses with 1.53 W peak power and 41-ps FWHM from an InGaAs/GasAs (970 nm) double-contact tapered semiconductor laser in a well defined single-lobed far-field.