Masaru Kazumura

Low-noise operation of a diode-pumped intracavity-doubled Nd:YAG laser using a Brewster plate

The authors demonstrate noise reduction which has been attained in a diode-pumped intracavity-doubled Nd:YAG laser by using a novel birefringent filter formed by a Brewster plate and a birefringent KTP crystal. It is confirmed that single longitudinal mode operation is obtained by the birefringent filter. As a result, the relative intensity noise obtained is less than -135 dB Hz. This noise reduction technique should play an important role for application of laser-diode pumped intracavity-doubled solid-state lasers. >

Feasibility of the LPE Growth of AlxGayIn1-x-yP on GaAs Substrates

The maximum direct bandgap energy of AlxGayIn1-x-yP lattice-matched to GaAs is found to be 2.17 eV at x=0.21 and y=0.34. This is the largest value among the III-V compounds with the zinc-blende structure. The phase diagram is calculated of the quaternary system Al–Ga–In–P. It is predicted that the LPE growth of AlxGayIn1-x-yP will encounter serious difficulties resulting from the extremely large segregation coefficient of aluminum. In fact, experiments have shown that aluminum is not incorporated into the crystals grown from the quaternary solutions because of the instant depletion of aluminum at the very early stage of the cooling process.

Variation of Liquid and Solid Compositions during LPE Growth from a Ternary Component Solution

A generalized calculation is presented to predict the variation of liquid and solid compositions during the liquid phase epitaxial growth from a ternary component solution under an equilibrium condition. Basic equations describing the fractional changes of liquid components are derived for the continuous process. Starting at a given initial condition the calculation based on an iterative procedure is carried out along on the theoretical liquidus surface with no adjustable parameters. The theory is applied to the growth of Ga1-XAlXAs as an example, resulting in good agreement with the experimental data.

A high-power GaAlAs superluminescent diode with an antireflective window structure

A novel high-power GaAlAs superluminescent diode (SLD) structure that introduces an antireflective (AR) window region into the rear side of the SLD is proposed. The light beam which travels backward is emitted from the edge of the active layer and diverges in the window region. Then the beam is reflected at the AR-coated rear facet only by a small percentage, a fraction of which couples into the active layer. Thus, this window structure gives a reduction of the reflectivity at the interface between the active layer and the window region so that lasing oscillation is successfully suppressed. An SLD operation of output power as high as 50 mW is obtained with a stable fundamental spatial mode. The spectral bandwidth at half maximum is about 15 nm over a wide output power range. >

Power-independent degradation of high-power GaAlAs lasers with nonabsorbing mirrors

The reliability of high-power single-mode GaAlAs lasers with nonabsorbing mirrors (NAMs) was investigated in detail. The lasers were tested at various output powers and temperatures. The aging test was performed under constant power in order to examine the output power dependence. In order to carry out the measurement with accuracy, the heat sink temperature was controlled with an error of +or-0.1 degrees C, and the operating current was measured every hour or every 10 h. As a result, very smooth aging test curves were obtained. Output powers of the coated lasers in the aging tests were 30, 50, and 100 mW, and the temperatures of the heat sink were 50, 70, and 90 degrees C. conventional lasers without a NAM were tested for comparison. The results indicate that the degradation of the lasers is dependent not on the output power, but on the operating current and temperature. The thermal activation energy and the degradation rate is estimated to be 0.85 eV. >

A high-power short-pulse laser diode for waveguide second harmonic generation

Abstract This paper describes successful development of a high-power short-pulse i.r. laser diode, together with numerical analyses giving a clear understanding of the operation. The novel aspect of the present laser diode is that a saturable absorber is incorporated for gain switching into the buried-twin-ridge substrate (BTRS) structure which allows a high-stability fundamental spatial mode operation. Peak powers as high as 1.23 W and pulse widths as narrow as 34.1 ps have been obtained in an efficient gain-switching operation with the high mode stability. The experimental observations are well-explicable by the numerical analyses in substantial respects. We also report picosecond-pulse blue-light generation which has been attained by applying the frequency doubling technique to the above laser in a LiNbO3 waveguide.

Power independent degradation of high power GaAlAs lasers with nonabsorbing-mirrors

The reliability of high-power single-mode GaAlAs lasers with nonabsorbing mirrors was investigated in detail. The lasers were tested at various output powers and temperatures. The results indicate that the degradation of the lasers is depen- dent not on the output power, but only on the operating current and temperature. The thermal activation energy of the degra- dation rate is estimated to be 0.85 eV, from which the lifetime under 100 mW operation at 25°C is expected to exceed 100 000 h.

Thickness dependence of output power and response time of double-heterostructure LED's.

The output power and the response time of a surface-emitting DH-LED are obtained theoretically by solving diffusion equations for excess electrons in terms of the active layer geometry. A significant difference in the output power is found between an n-side up diode and a p-side up diode owing to absorption loss in the active layer. The optimum thickness for each type is predicted. It is also shown that the sinusoidal modulation bandwidth and the rise time strongly depend on the active layer thickness as well as the interface recombination velocity. The analytical results are in agreement with experiment.