A slab of intrinsic GaAs, 3cm long, 2cm wide, and 0.3cm thick, is exposed to light. The light is absorbed with an absorption coefficient a=500cm-1 (this means that the light intensity decreases in the material exponentially with distance t, and is proportional to exp(-at)). The light is monochromatic with a wavelength of 750nm and an intensity of 5×10-4W/cm2. (Photon energy (eV) is given by 1.24/wavelength (µm).)
What photon flux is incident on the slab?