Novel surface-sensitive diode lasers for chemical detection

A novel near-infrared diode laser having sensitivity to change of absorption and refractive index at its surface- sensitive region is presented. This semiconductor laser utilizes an AlGaAs single quantum well structure emitting at a wavelength of 950 nm, and its dimensions are 1 mm X 0.5 mm X 0.2 mm. One of the cladding layers is thinned such that the evanescent wave in the quantum well interacts with a surface-sensitive region on the laser. A theoretical model of laser sensitivity toward changes in absorption of a dye- doped polymer coating is formulated. Experimental data using the surface-sensitive diode laser for sensing ammonia and adsorbed monolayers of molecular films are presented. The output power, threshold current and wavelength are shown to be affected by the changes in the adsorbed coating.