Harold D. Edmonds

Second-harmonic generation with the GaAs laser

The second harmonic of pulsed GaAs injection lasers was generated with the nonlinear crystal α-iodic acid (HIO 3 ) phase matched by angular tuning. The injection laser was operated with an external cavity, and the HIO 3 crystal was placed inside the cavity to increase the conversion efficiency. The maximum harmonic power observed was 15 μW with a fundamental power of 4.5 watts inside the cavity. Since the lasing bandwidth was typically 30 A and the calculated bandwidth for collinear harmonic generation was only 6.3 A, a grating was used to narrow the lasing bandwidth to 3 A. The expected large increase in harmonic power did not occur. It is shown that this is due to sum-frequency generation by laser modes lying outside the harmonic bandwidth. It is also found that the spectral width of the harmonic becomes bigger than the collinear bandwidth when a divergent laser beam is used.

A monolithic light-emitting-diode display

A monolithic 5 × 7 array of planar diffused p-n junctions in GaAs 1-x P x (x≃0.38) has been built for a light-emitting diode (LED) alphanumeric readout. A character formed by this readout is 0.246 cm high and 0.170 cm wide. The monolithic chip has all p-n junctions, n-contacts, p-contacts, interconnections and terminal metallurgy on the epitaxial layer which represents a departure from the conventional methods of making LED arrays, namely wire bonding discrete chips with contacts on two sides in a hybrid configuration. Each LED in the array is connected to one of the terminals arranged around the periphery of the chip and individually addressed by direct current from a driver on a silicon control chip. For each character position in a display there is one monolithic LED chip and one monolithic silicon control chip solder joined to terminals on a glass plate and interconnected by Cr-Cu-Cr lines evaporated onto the glass substrate. The display is addressed by serial information provided from an ROM which is read into a 35-stage shift register on the control chip which controls the drivers. Thus with two standard parts, any N-character display can be fabricated with considerable reduction in handling since no discrete elements or wire bonds are used.