No abstract

We studied the lifetimes of photoexcited carriers in H+ bombarded InP for different damage doses by means of femtosecond luminescence spectroscopy. The lifetime decreases down to 95 fs for a dose of 1×1016 cm−2. To our knowledge this is the shortest decay time for spontaneous light emission ever observed. The luminescence spectrum of the most damaged sample is inverted, indicating nonthermalized carrier distributions.

The ultrafast relaxation of minority electrons in highly doped p-GaAs (p = 1.0 x 10'9~m-3) has been investigated through femtosecond time-resolved luminescence. For low excitation densities the hole plasma temperature stays at 300 K and the transient luminescence spectra reveal the rapid cooling of the minority electrons within the first picoseconds. The electron-hole energy transfer is much larger (up to IO-'W) than the known electron-Lo phonon scattering rate, which allows the quantitative determination of the electron-hole energy transfer.

Diabetic macular edema is shown to be treated successfully by central focal argon laser coagulation in most cases. Since February 1986, diabetic patients with macular edema were evaluated prospectively and treated by focal argon laser coagulation and/or grid pattern. A second group of diabetic patients with comparable macular edema and similar retinal changes was explored retrospectively. Visual acuity after treatment in relation to preoperative visual acuity was measured and statistically compared with visual acuity of the second group without laser treatment. The results show that laser treatment is important for stabilization of visual acuity but does not increase visual acuity beneath 0.2. Indications for treatment are discussed.

We have fabricated submicron GaAs crystals by pulverization of bulk material. Size selected crystals exhibit modified photoluminescence spectra with blue shifts of up to 10 meV. The observed behavior is explained by the enhancement and the inhibition of spontaneous emission in a three-dimensional optical microcavity formed by a semiconductor microcrystal.