Together with the introduction of topological light waves (light with phase or polarization singularities), their generation and applications were described. Using a photonic crystal, axially-symmetric polarizer or mirror, 1) supercontinuum optical vortex generation ranging ∼500 to ∼800 nm without spatial nor topological-charge dispersions, 2) generation of ultrabroadband axially-symmetric polarization modes ranging ∼600 to ∼800 nm without polarization dispersion, and 3) a high power radially-polarized light generation directly from a diode-pumped Nd:YVO4 bounce amplifier were experimentally demonstrated. As applications of generated topological light waves, 4) laser ablation of Ta plates using nanosecond optical vortex pulses and, in particular, using spin-orbit interactions of light, microneedle fabrication on a metal surface by laser ablation were performed.
We investigated spin-controlled semiconductor lasers which can emit circularly polarized coherent light by utilizing electron spin polarization and the optical selection rule. We fabricated a (110)-oriented vertical-cavity surface-emitting laser (VCSEL) with GaAs/AlGaAs quantum wells (QWs) and characterized lasing properties of the VCSEL under optical spin injection. Circularly polarized lasing with a high degree of circular polarization of 0.96 in the VCSEL was demonstrated at room temperature originating from a long electron spin relaxation time in the (110) GaAs QWs. We also demonstrated a tenfold modulation of electron spin relaxation time from 4 to 0.3 ns in the (110) GaAs QWs through the Rashba spin-orbit coupling induced by applying an external electric field at room temperature.
We focus on our recent study of coherent phonons in wide-gap semiconductors. The principle and advantage of spectrally filtered EO sampling pump-probe transmittance detection of coherent phonons in transparent media are explained. Even though using noncollinear optical parametric amplifier with low repetition rate, we could clearly observe the coherent phonon signal. We studied resonant generation of coherent phonon in ZnTe by a nondegenerate pump-probe measurement. The pump energy dependence of the initial amplitude can be explained by the intense absorption of the pump pulse.
We investigate the dephasing mechanism of optically-induced exciton coherence in an ensemble of InAs self-assembled quantum dots (QDs) using a two-pulse photon-echo (PE) technique. The sample was fabricated on an InP (311)B substrate using strain compensation to control the emission wavelength. This technique also enabled us to fabricate a 150-layer stacked QD structure for enhancing the PE signal intensity. We show the measured decay time of PE signal intensity for resonant excitation of ground-state transition is extremely long, which corresponds to ultralong coherence times of excitons in our QDs. We confirmed that non-radiative population relaxation and pure dephasing are considerably smaller than the radiative relaxation at low temperature. Furthermore, we demonstrate the ultrafast coherent control of QD exciton polarization by changing the pulse areas (Rabi oscillations) in the PE experiment. We also propose a new scheme for implementing QD quantum memory by using the PE technique.
Recent works of the authors on quantum information science using photons are reviewed. After the general introduction of photonic quantum information science, unique nano photonic devices such as tapered optical fibers, microsphere resonators, and nano diamond crystals are explained and their relationship with surface science is discussed. In the latter half, the realization of optical quantum circuits, and the application of such quantum circuits for quantum metrology are explained.
Scanning tunneling microscopy (STM) based techniques combined with optical excitation enable us to analyze a variety of functional properties of nano-materials and nano-devices. A review of several works on photo-assisted STM is presented. It is shown that spatially resolved Fourier-transform photo-absorption spectra of individual GeSn nanodots, obtained by a technique based on STM, exhibited a distinct peak far below the absorption edge of the Si substrate, which showed a clear blue shift with decreasing dot size. The energy position of the peak was in good agreement with the optical transition energy between discrete levels predicted by the quantum-confinement size dependence.
Recent developments of terahertz time-domain attenuated total reflection spectroscopy (THz TD-ATR) have been reviewed. The technique has been applied to study water dynamics in terahertz region and hydration effect of bio-related molecules in water solutions.
A white-light laser source is applied to coherent anti-Stokes Raman scattering (CARS) microspectroscopy. Owing to the ultra-broadband spectral profile of the white-light laser, a wide range of vibrational resonances can be investigated. Using the white-light laser source, we successfully visualized living cells with vibrational contrast.
The ‘magic frequency’ protocol has made it possible to design new type of atomic clocks based on well-engineered perturbations. Such ‘optical lattice clocks’ will allow extremely precise and speedy timekeeping, which targets fractional uncertainty of 10-18, by using a large number of atoms and by sharing ‘magic frequency’ protocol. This paper covers motivations for developing such clocks and their experimental realizations. Possible impacts and future applications of optical lattice clocks are discussed, such as testing the fundamental laws of physics and developing relativistic geodesy.
Quantum teleportation is a transfer protocol of quantum states, which cannot be realized only with classical physics. The essence of this protocol is quantum entanglement, which was proposed by Einstein as a counter example for quantum mechanics. In terms of quantum information processing, quantum teleportation can be regarded as an “Identity” operation. So one can modify the quantum circuit to make an arbitrary operation and universal quantum computing. One of the application of the quantum computing is “quantum version of coherent communication”, which enables us to get the channel capacity beyond the classical limit (Shannon limit).
In this study, carbonaceous material was prepared from waste cotton (CT1000). Yield, base consumption, pH, specific surface area, pore volume, and mean pore diameter of CT1000 were investigated. Specific surface area and pore volume of CT1000 was greater than that of CT (virgin waste cotton). Kayacryl Yellow (KY: yellow dye) was used for adsorbate. The equilibrium adsorption was reached within 48 h. The adsorption rate data was fitted to the pseudo-second-order kinetic equation, which indicated that reaction rate was in proportion to the square of adsorbate concentration in aqueous solution systems. Moreover, the adsorption isotherm data was fitted to the Freundlich equation. Amount of KY adsorbed onto CT1000 in the presence of dye assistant auxiliaries was similar trend to that onto CT1000 in the absence of dye assistant auxiliaries. These results showed that CT1000 was useful for purification of wastewater containing dyestuffs.