Effects of neutron fluence on the operating characteristics of diode lasers used in atomic frequency standards

An experiment to study the effects of neutron fluence on the operating characteristics of transverse junction stripe (TJS) AlGaAs diode lasers is described. Different models of the TJS diode laser produce optical radiation in both the 780 and 850 nm range, appropriate for optical pumping in rubidium and cesium atomic clocks, respectively. A set of TJS diode lasers was exposed to a neutron fluence of 2×10 ¹² n/cm², and four laser characteristics were examined after each exposure. The laser´s light output versus injection current and single-mode linewidth versus output power both influence the efficiency of optical pumping and hence the atomic clock´s signal-to-noise ratio. The laser´s single-mode wavelength versus injection current (laser tuning) was measured. The diode laser´s gain curve was studied at several injection currents below threshold. This diode laser characteristic is taken as an indicator of the neutron damage mechanisms in the laser´s semiconductor material. It was found that neutron exposure can lead to tuning curve modifications, increased spectral linewidths, and reduced output powers