InP nanowire light-emitting diodes with different pn-junction structures.

We report on the characterization of wurtzite (WZ) InP nanowire (NW) light-emitting diodes (LEDs) with different pn junctions (axial and radial). The series resistance tended to be smaller in the NW-LED using core-shell InP NWs with a radial pn junction than in the NW-LED using InP NWs with an axial pn junction, indicating that radial pn junctions are more suitable for current injection. The electroluminescence (EL) properties of both NW LEDs revealed that the EL had three peaks originating from the zinc-blende (ZB) phase, WZ phase, and ZB/WZ heterojunction. Transmission electron microscopy showed that the dominant EL in the radial pn junction originated from the ZB/WZ interface across the stacking faults.

Simple method to determine the gain and saturation irradiance of a laser.

A new method is proposed to determine the gain parameter and the saturation irradiance of a partially homogeneously broadened gaseous laser medium in a unidirectional ring cavity. The proposed method is applied to a He-Xe 3.5-microm line, and the gain parameter and the saturation irradiance are then determined to be 0.0665 cm(-1) and 4.69 microW/mm(2), respectively. The method developed here is expected to be more accurate than conventional methods such as that using more than one laser and that with frequency detuning because less ambiguity is involved in the experiments and the theoretical treatment.

Second-harmonic generation in amorphous vinylidene cyanide/vinyl acetate copolymer using a pulsed Nd:YAG laser.

Second-harmonic generation was recently observed in an amorphous vinylidene cyanide/vinyl acetate copolymer film by using a pulsed Nd:YAG 1.06-microm laser.

Statistical measurements of irradiance fluctuations of a multipass laser beam propagated through laboratory-simulated atmospheric turbulence.

Experimental results are presented for the statistics of 0.6328-microm laser irradiance fluctuations for multiple-pass propagation through a laboratory-simulated atmospheric turbulence of strength C(2)(n) = 2.476 x 10(-11) m(-2/3) and the smallest scale size l(0) = 2.74 mm. The coefficients of variation gamma(0), skewness gamma(1), and excess gamma(2) of irradiance fluctuations are plotted as a function of path length. From the plots of gamma(2) vs gamma(1) for various values of sigma(2)(1) (= 1.23 k(7/6) C(2)(n)L(11/6)) in different regions within the turbulence, the following forms of the probability distribution functions for the irradiance fluctuations are considered: lognormal, Rice-Nakagami, m distribution, gamma (and exponential), and K distribution. We have also demonstrated the characteristic feature of -8/3 power law behavior of power spectrum and the shift of Tatarski's peak frequency in the case of strong turbulence.

Atmospheric turbulence chamber for optical transmission experiment: characterization by thermal method.

A turbulence chamber (0.78 x 0.23 x 2.59 m(3)) consisting of ten small electric heater/blowers with an aluminum foil screen and three screens of 2-mm aluminum wire meshes can generate the nearly homogeneous isotropic turbulence within the 0.5 x 0.05 x 2-m(3) region at the 0.11-m height of optical measurements. The temperature structure constant squared C(2)(T) = 52.9 K(2) m(-?) was obtained from the temperature structure function measurements measured by using a differential microthermocouple system. The refractive-index structure constant squared C(2)n_{at the 632.8-nm wavelength was calculated from C(2)(T):C(2)(n) = 3.00 x 10(-11)m(-?). The average wind velocity and temperature were 0.41 m/sec and 53 degrees C, respectively. From the power spectrum of temperature fluctuations, the inner and outer scales of turbulence are determined: l(o) = 5.0 mm and L(0) = 6.5 cm. The measured temperature structure function and power spectrum of temperature fluctuations satisfy the ? and -5/3 power similarity laws in the inertial subrange, respectively.}