Katsumi Yoshino

Flexible mirrorless laser based on a free-standing film of photopolymerized cholesteric liquid crystal

Optically pumped mirrorless laser action has been observed in a dye-doped flexible free-standing film of photopolymerized cholesteric liquid crystal (PCLC). In the PCLC film, self-organized helical structure acts as one-dimensional (1D) photonic crystal. At high excitation intensity above the threshold, a laser action is observed at an edge of the 1D photonic band of the PCLC helical structure. This PCLC film laser possesses an excellent mechanical flexibility, and the laser action is also observed in a bent film of PCLC. This implies that the one-dimensional periodic structure for the laser action is maintained even in the deformed film. Using such flexibility of the PCLC film, a focusing effect of laser emission is demonstrated in a circularly deformed film. Moreover, the helical pitch of the PCLC has no temperature dependence in contrast to that of unpolymerized cholesteric liquid crystal. This means that the operation wavelength of laser action is thermally stable, which is the great advantage for the...

Discontinuous Shift of Lasing Wavelength with Temperature in Cholesteric Liquid Crystal

The laser action in a dye-doped cholesteric liquid crystal has been investigated as a function of temperature. The discontinuous shift of the lasing wavelength has been observed. It has also been found that the shift of the stop band in the cholesteric liquid crystal is discontinuous when the size of the measured area for the spectrum is small. These results have been interpreted to originate from the disappearance of every half period of the cholesteric liquid crystal helix in the unwinding process as the temperature decreases.

Electro-Tunable Defect Mode in One-Dimensional Periodic Structure Containing Nematic Liquid Crystal as a Defect Layer

Electrical tuning of defect modes in a one-dimensional periodic structure has been demonstrated using a nematic liquid crystal as a defect layer in the periodic structure. The wavelength of the defect mode shifts upon applying the electric field, which is due to the refractive index change in the defect layer caused by the field-induced realignment of the liquid crystal molecules. The theoretical calculation based on a simple transfer matrix has been carried out, and the result has been found to agree with the experimental result.

Electrically tunable waveguide laser based on ferroelectric liquid crystal

Laser action in a waveguide configuration has been demonstrated in a planar alignment cell of dye-doped chiral smectic liquid-crystal mixtures with a short pitch helical structure. In this configuration, doped dye can effectively be excited by a pump beam illuminating perpendicularly the helical axis and the laser light emitted along the helical axis propagates in the waveguide. Lasing wavelength can be tuned by adjusting the periodicity of the helical pitch upon applying the electric field.

Fabrication of Flexible Distributed Feedback Laser Using Photoinduced Surface Relief Grating on Azo-Polymer Film as a Template

An all-polymer flexible distributed feedback (DFB) laser has been fabricated using a photoinduced surface relief grating (SRG) on an azo-polymer film as a template. The holographically induced SRG on the azo-polymer was transferred onto a flexible film of a UV-curable photopolymer. Optically pumped mirrorless DFB laser action was observed from a conducting polymer, poly(2-methoxy-5-dodecyloxy-p-phenylenevinylene) (MDDO-PPV), spin-coated on the transferred SRG.

Electro-tunable laser action in a dye-doped nematic liquid crystal waveguide under holographic excitation

Optically pumped distributed feedback lasing has been demonstrated in a dye-doped nematic liquid crystal (NLC) waveguide by holographic excitation. The excitation was performed by two-beam interference using Lloyd mirror configuration. With an applied electric field, continuous tuning of the lasing wavelength was realized due to the change of the effective refractive index of the NLC core layer caused by the reorientation of NLC molecules.

Tunable laser action in a dye-doped nematic liquid-crystal waveguide under holographic excitation based on electric-field-induced TM guided-mode modulation

Electrically tunable laser action has been demonstrated in a dye-doped nematic liquid-crystal (NLC) waveguide by holographic excitation. The optical feedback was provided by the distributed feedback induced by two-beam interference by use of the Lloyd mirror configuration. Electrical tuning of the lasing wavelength was realized owing to the change of the effective refractive index of the NLC core layer caused by the reorientation of NLC molecules. On the basis of a waveguiding mode theory, numerical analysis of a TM guided mode in the presence of an applied electric field was performed, and field-induced tuning of the lasing wavelength was investigated in detail. Prospects for the realization of a single-mode operation and tuning of the lasing wavelength were also shown.

Thermal Photodetector Using Freely Suspended Liquid-Crystal Film

We show that freely suspended liquid-crystal film have suitable properties for use as visible and infrared radiation sensors. The replacement of the polymer film in a Golay cell by a liquid-crystalline film results in the effective increase of the sensor response rate (100 times) without undue sacrifice of its sensitivity.

Single-Mode Operation of Electrotunable Laser in a Dye-Doped Nematic Liquid-Crystal Waveguide under Holographic Excitation

Optically pumped distributed feedback (DFB) lasing has been demonstrated in a dye-doped nematic liquid-crystal (NLC) waveguide by holographic excitation. Utilizing NLC with a low refractive index, the single-mode operation of a laser action was realized. With an applied electric field, continuous tuning of the single-mode lasing wavelength was realized due to the change in the effective refractive index of the NLC core layer caused by the reorientation of NLC molecules.

Relaxation kinetics of photoinduced surface relief grating on azopolymer films

The relaxation kinetics of the photoinduced surface relief grating (SRG) formed on an azopolymer film after stopping laser beam writing has been systematically investigated. In addition to a photoinduced increase of the diffraction efficiency in the SRG, an anomalous further enhancement of the efficiency was observed even without light irradiation, after the recording light beam was switched off. This anomalous relaxation process consists of two components with short and long relaxation times, and strongly depends on the temperature and polarization of the probe beam used for the diffraction measurement. At lower temperatures the anomalous growth is more effective and the fast component is dominant. From the results of the polarization dependence of the diffraction efficiency and optical absorption, it has been manifested that the fast component of the relaxation originates from the cis-trans thermal isomerization of azobenzene in the side chain. The origin of the slow decay is also discussed in terms of ...