Volume 89, Issue 6, 15 March 2001
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
89(2001); http://dx.doi.org/10.1063/1.1347953View Description Hide Description
A tunable laser operating near 944 nm is important for the detection of water vapor in the atmosphere. In this work, we have carried out a systematic study of Nd doped fiber glassmaterials which can be used for this purpose. The emission cross sections of these materials at 944 nm have been calculated. The wavelength dependence of emission of these materials has been studied. Among the silica-based materials Nd doped silica fiber glass has the largest cross section for 944 nm laser emission. The codopants reduce this cross section. Some Nd doped nonsilica materials such as and chloride glass have higher stimulated emission cross section than silica-based materials.
Self-consistent solutions to the intersubband rate equations in quantum cascade lasers: Analysis of a device89(2001); http://dx.doi.org/10.1063/1.1341216View Description Hide Description
The carrier transition rates and subband populations for a GaAs/AlGaAs quantum cascade laser operating in the mid-infrared frequency range are calculated by solving the rate equations describing the electron densities in each subband self-consistently. These calculations are repeated for a range of temperatures from 20 to 300 K. The lifetime of the upper laser level found by this self-consistent method is then used to calculate the gain for this range of temperatures. At a temperature of 77 K, the gain of the laser is found to be when only electron–longitudinal-optical phonon transitions are considered in the calculation. The calculated gain decreases to when electron–electron transition rates are included, thus showing their importance in physical models of these devices. Further analysis shows that thermionic emission could be occurring in real devices.
In situ temperature measurements via ruby R lines of sapphire substrate based InGaN light emitting diodes during operation89(2001); http://dx.doi.org/10.1063/1.1349858View Description Hide Description
The temperature of encapsulated green and ultraviolet light emitting diodes(LEDs) in operation has been measured optically via the rubyR lines emitted by the residual contaminations in the sapphire substrate. These two photoluminescent R lines, which are excited by the electroluminescence of the LED itself, show a well-characterized line shift as a function of temperature and pressure. The temperature is found to rise linearly with the applied forward current of the LED at a rate of ≈1 K/mA. This optical temperature measurement based on monitoring the two rubyR lines could qualify as a sensitive method for an in situ temperature sensor for other sapphire substrate based semiconductor devices such as laser diodes and field effect transistors.