Terahertz bandpass filter with Babinet complementary metamaterial mirrors and silicon subwavelength structure.

We fabricated a rigid bandpass filter with a broad far-infrared wavelength range of high transmission using a silicon subwavelength structure with a Babinet complementary metamaterial half-mirror pair, despite its apparent light-blocking structure. The rigid one-piece filter was produced by a simple process involving photolithography, dry etching, and deposition, each performed only once. The transmission principle relies on the Fabry-Perot resonance with a metamaterial half-mirror pair that exhibits extraordinary optical transmission due to spoof surface plasmon polaritons. The transmission center wavelength was successfully predicted by the basic equation of Fabry-Perot resonance with an effective medium approximation. In contrast, a narrower bandwidth and a lower minimum transmittance than those predicted from the basic equation were provided by the subwavelength Si structure between the metamaterial mirrors, resulting in enhanced bandpass filter characteristics.

Benzothienobenzothiophene-Based Molecular Conductors: High Conductivity, Large Thermoelectric Power Factor, and One-Dimensional Instability.

On the basis of an excellent transistor material, [1]benzothieno[3,2-b][1]benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)2XF6 (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room-temperature conductivity amounts to 4100 S cm(-1) in the AsF6 salt, corresponding to the drift mobility of 16 cm(2) V(-1) s(-1). Owing to the high conductivity, this salt shows a thermoelectric power factor of 55-88 µW K(-2) m(-1), which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4kF charge-density waves as an origin of the low-temperature insulating state.

Pr3+:YLF mode-locked laser at 640 nm directly pumped by InGaN-diode lasers.

We attain stable mode-locking of an InGaN laser-diode-pumped Pr3+:YLF laser with a pump power of 2.8 W using a semiconductor saturable absorption mirror. A maximum averaged output power of 65 mW was obtained with a 45-ps pulse width at a pulse repetition rate of 108 MHz. We also attempted Kerr-lens mode-locking by employing an SF57 glass in a cavity as a Kerr medium.

50-kHz, 50-ns UV pulse generation by diode-pumped frequency doubling Pr3+:YLF Q-switch laser with a Cr4+:YAG saturable absorber.

We demonstrate intracavity second-harmonic generation at 320 nm of a diode-pumped praseodymium-doped YLF laser Q-switched by a Cr4+:YAG crystal. By employing two 3.5-W high-power blue InGaN diode lasers as the pump source, we obtained 50-ns Q-switched pulses with a pulse energy of 1.54 µJ at a repetition rate of 50 kHz. A rate equation analysis shows good agreement with the experimental results.

Saturation of 640-nm absorption in Cr4⁺:YAG for an InGaN laser diode pumped passively Q-switched Pr³âº:YLF laser.

We measure the absorption recovery time, the ground- and excited-state absorption cross sections of a Cr4+:YAG crystal at 640 nm for the first time. A pump-probe measurement reveals the existence of two recovery times of 26 ns and 5.6 µs. By a Z-scan experiment, the ground- and excited-state absorption cross sections are estimated to be 1.70 - 1.75 × 10(-17) and 0.95 - 1.00 × 10(-17)cm2, respectively. The adequacy of the proposed model and the accuracy of the estimated parameters of the saturable absorber are verified by reproducing the experimentally obtained performance of a passively Q-switched Pr3+:YLF laser with the Cr4+:YAG saturable absorber from rate equation analysis.

Transistor properties of salen-type metal complexes.

Schiff base complexes derived from salicylaldehyde and ethylene-, propylene-, and trans-1,2-cyclohexane-diamines exhibit p-channel transistor properties. The Cu complexes are open-shell compounds, but the oxidation and the hole transport occur at the highest occupied molecular orbital, where the singly occupied molecular orbital (SOMO) does not participate in conduction. Although Ni complexes tend to show larger mobilities than Cu complexes owing to the molecular planarity, the presence of SOMO is not harmful to the transistor properties.

Impact of bulky phenylalkyl substituents on the air-stable n-channel transistors of birhodanine analogues.

By introducing bulky 2-phenylethyl groups into sulfur-rich electron acceptors, 5,5'-bithiazolidinylidene-2,2'-dione-4,4'-dithione and 5,5'-bithiazolidinylidene-2,4,2',4'-tetrathione, electron transport with the mobility of 0.27 cm2 V-1 s-1 with ambient and long-term stability is achieved in thin-film transistors. Bulky groups destroy the intermolecular S-S network, but the long-term transistor stability is maintained. Here, benzyl groups realize one-dimensional stacking structures, whereas 2-phenylethyl groups lead to herringbone structures.

Carrier Charge Polarity in Mixed-Stack Charge-Transfer Crystals Containing Dithienobenzodithiophene.

Dithieno[2,3- d;2'3'- d']benzo[1,2- b;4,5- b']dithiophene forms mixed-stack charge-transfer complexes with fluorinated tetracyanoquinodimethanes (F nTCNQs, n = 0, 2, and 4) and dimethyldicyanoquinonediimine (DMDCNQI). The single-crystal transistors of the F nTCNQ complexes exhibit electron transport, whereas the DMDCNQI complex shows hole transport as well. The dominance of electron transport is explained by the superexchange mechanism, where transfers corresponding to the acceptor-to-acceptor hopping ( teeff) are more than 10 times larger than the donor-to-donor hopping ( theff). This is because the donor orbital next to the highest occupied molecular orbital makes a large contribution to the electron transport owing to the symmetry matching. Like this, inherently asymmetrical electron and hole transport in alternating stacks is understood by analyzing bridge orbitals other than the transport orbitals.