Kazuyoshi Kuroyanagi

Second Order Nonlinear Optical Properties of the Single Crystal of N-Benzyl 2-methyl-4-nitroaniline: Anomalous Enhancement of the d333 Component and Its Possible Origin

A single crystal of N-benzyl 2-methyl-4-nitroaniline (BNA) whose dimensions were 8×10 mm (diameter × length) was grown using a vertical Bridgman method with sufficient optical transparency for spectroscopic use. Polarized reflection spectra of the crystal were measured in order to determine its linear optical parameters (refractive indices and extinction coefficients). The relative magnitudes of the d-tensor components of the crystal were determined to be d333=(17±9)×d322, d322>d311, d311~0 from polarization dependencies of the second harmonic generation. These results are in disagreement with previously reported theoretical studies, in which the effects of intermolecular interactions were completely neglected. Here, we have included these intermolecular interactions in the calculations assuming the presence of supra-molecular clusters. We conclude that the anomalous enhancement of d333 is due to the interactions along the direction of the hydrogen bonds in the crystal and the resonance effect.

All Organic Terahertz Electromagnetic Wave Emission and Detection Using Highly Purified N-Benzyl-2-methyl-4-nitroaniline Crystals

We studied terahertz (THz) electromagnetic wave emission and detection using highly purified N-benzyl-2-methyl-4-nitroaniline (BNA) crystals. In THz emission experiments, we compared the efficiencies of THz emission via optical rectification for BNA, ZnTe, and GaP crystals, and confirmed that the BNA crystal is the most efficient THz emitter among these three crystals within the frequency range limits for observation. In the THz detection experiment, we also compared the modulation efficiencies of the BNA and ZnTe crystals, and found that the ZnTe crystal has a higher efficiency than the BNA crystal. However, the BNA crystal has a higher efficiency than the ZnTe crystal in high-frequency regions. Since the BNA crystal is suitable for detecting a high-frequency region even when using thick crystals, it is expected that the BNA crystal as a THz detector will be easy to prepare and handle.

Determination of Refractive Indices and Absorption Coefficients of Highly Purified N-Benzyl-2-methyl-4-nitroaniline Crystal in Terahertz Frequency Regime

We have measured the refractive index and absorption coefficient of the N-benzyl-2-methyl-4-nitroaniline crystal using terahertz time-domain spectroscopy. We found that the refractive index had a value between 1.5 and 1.9 in the direction and between 1.9 and 2.3 in the direction. We also found that there were resonances at 1.6 and 3.2 THz in the direction, and 1.3, 2.2, and 3.6 THz in the direction within the observed spectral range between 0 and 5 THz. A Lorentz-type oscillator model is applicable to explain our experimental observations.

Simultaneous Observation of Coherent GaSb-like and AlSb-like Longitudinal Optical Phonons in GaSb/AlSb Superlattices

We have investigated coherent longitudinal optical (LO) phonons in GaSb/AlSb superlattices. The coherent AlSb-like LO phonon in the barrier layer and the coherent GaSb-like LO phonon in the well la...

ELECTROLUMINESCENCE IN UNDOPED GAAS/ALAS SUPERLATTICE DUE TO AVALANCHE BREAKDOWN

We have observed electroluminescence (EL) in an undoped GaAs/AlAs superlattice (SL) originating from avalanche breakdown. From EL and photocurrent-voltage characteristics, we found that a large number of electrons were injected into Γ2 states in the SL by avalanche breakdown under a high electric field. The EL spectra revealed two peaks: one having a longer wavelength originated from the radiative recombination process between Γ1 and hh1 states, while the other peak originated from the recombination between Γ2 and hh1 states.

Avalanche breakdown mechanism originating from Γ–X–Γ transfer in GaAs/AlAs superlattices

An avalanche breakdown mechanism in GaAs/AlAs type-I superlattices is demonstrated. This mechanism shows its power at a bias voltage where both of the following two conditions are met. One is electron transfer from the Γ ground state to the X ground state (Γ1-X1), and the other is the escape of electrons from the X1 state to the second Γ state (X1-Γ2). Under both conditions, because the AlAs barriers become transparent for electron transport due to the Γ1-X1-Γ2 path, the drift speed (i.e., the acceleration of electrons) grows, and then the superlattice shows the phenomenon of avalanche breakdown. From our experimental results for various GaAs/AlAs superlattices, it is thought that such avalanche breakdown frequently occurs when type-I GaAs/AlAs superlattices have thick barrier widths.

Incident light polarization dependence of terahertz emission spectrum of crystalline 4‐N,N-dimethylamino-4′‐N′-methyl-stilbazolium tosylate

In this work we have measured the dependence of terahertz emission via optical rectification from the 4‐N,N-dimethylamino-4′‐N′-methyl-stilbazolium tosylate crystal as a function of incident light polarization. Many structures, which varied depending on the polarization of the incident pulse, were observed in the frequency spectra. The observed structures can be explained by incorporating the refractive index dispersion, the response function, and the birefringence properties of the crystal into the mathematical model used to reconstruct the experimental data. Our results show that careful attention must be paid to these three properties when enhancing nonlinear susceptibility during the fabrication of efficient terahertz emitters.

All solid-state Cr:LiSAF laser

Many kinds of experiments about all solid-state Cr:LiSAF lasers have been reported. A tunable all solid-state cw laser having tunability over more than 100 nm was developed by using the spectrum selection self-injection locking (SSSIL) method in 1992. The authors realize tunable picosecond radiation from an all solid-state laser with 146-200 ps pulses in an 88 nm range. Also, 70 fs pulse generation was achieved using a Kerr-lens mode-locking pumped with an Ar/sup +/ laser. >

Photoluminescence from high Γ-electron subbands and intersubband electroluminescence using X-Γ carrier injection in a simple GaAs/AlAs superlattice

We report the interband photoluminescence from high Γ-electron subbands and mid-infrared electroluminescence originating from an intersubband transition in a simple GaAs (15.3 nm)/AlAs (4.5 nm) superlattice embedded in a p–i–n structure. Interband photoluminescence properties under applied bias voltages provide conclusive evidence that electrons populate the fourth Γ (Γ4) electron subband in the GaAs layer. This electron population results from the carrier injection into the Γ4 subband from the adjacent X1 subband in the AlAs layer, which is initiated by the X1–Γ4 resonance. We calculate the overlap integral of the envelope functions for Γ-electron and heavy-hole subbands in order to discuss the carrier population in high Γ subbands based on the photoluminescence intensities. The results of analysis suggest that a population inversion can be obtained between the Γ4 and Γ3 subbands under the X1–Γ4 resonant condition. The energy of the intersubband electroluminescence, 100 meV, agrees with the energy spacing between the Γ4 and Γ3 subbands. This demonstrates that the carrier injection into the higher Γ subband using X–Γ scattering will be useful for designing of intersubband-emission devices.

Intersubband electroluminescence using X−Γ carrier injection in a GaAs/AlAs superlattice

We report midinfrared electroluminescence originated from an intersubband transition in a GaAs/AlAs superlattice consisting of asymmetric double quantum wells. It is confirmed from interband photoluminescence properties under applied bias voltages that electrons populate at the second Γ (Γ2) subband in the GaAs layer. The electron population results from the carrier injection into the Γ2 subband from the adjacent X1 subband in the AlAs layer, which is initiated by the X1–Γ2 resonance. The energy of the intersubband electroluminescence, 190 meV, agrees with the energy spacing between the Γ2 and Γ1 subbands. This demonstrates that the carrier injection into the higher Γ subband using X–Γ scattering is useful for the design of intersubband-emission devices.