Mr. Hiroki Yamaoka Profile

Hiroki Yamaoka

at Keio Univ

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Proceedings Article | 27 August 2009 Paper

Lasing characteristics of optically pumped edge-emitting organic semiconductor laser with 4,4'-bis[(N-carbazolyl)styryl] biphenyl

Kenji Shirakawa, Hiroki Yamaoka, Yasuhiro Toriyama, N. Shinichi Takahashi, Chihaya Adachi

Proceedings Volume 7415, 74151H (2009) https://doi.org/10.1117/12.825451

KEYWORDS: Optical pumping, Semiconductor lasers, Resonators, Organic semiconductors, Laser optics, Polishing, Silica, Liquids, Nitrogen, Picosecond phenomena

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Recently, we have presented optically-pumped edge-emitting organic laser devices consisting of Alq3:DCM film (5% DCM) deposited onto a polished GaAs (100) substrate coated with an 1-um-thick layer of RF sputtered SiO₂ using cleaving method. The threshold density was typically 3 μJ/cm² in a sample with a cavity length of 5 mm. The internal loss α and the gain coefficient β were found to be about 10.5 cm^-1 and 3.2 cm-μJ^-1, respectively. BSB-Cz has quite-high efficiency as blue laser material. In this work, organic laser devices of CBP:BSB-Cz film (6% BSB-Cz) were vacuum-deposited onto a polished GaAs (100) substrate coated with an 1 um-thick layer of RF sputtered SiO₂. The cleaved samples were optically pumped by a N₂ gas laser (wavelength: 337 nm) with a pulse width of 600 ps at a repetition rate of 20 Hz. We investigated emission spectrum, emission intensity and the full width at half maximum (FWHM) by varying excitation intensity. Pumping a sample with a cavity-length of 5 mm, emission intensity drastically increased at certain. The FWHM drastically narrowed as the emission intensity was increased. The threshold density was 1.40 μJ/cm² with a cavity length of 5 mm, it was half as much as Alq3:DCM. The internal loss α and the gain coefficient β were found to be about 5.57 cm^-1 and 6.72 cm-μJ^-1. We found BSB-Cz material have higher efficiency than Alq3:DCM. Moreover, polarization characteristics. And the threshold density cavity length relationship were investigated.

Proceedings Article | 16 October 2007 Paper

Lasing characteristics of optically pumped edge-emitting organic semiconductor laser

Hiroki Yamaoka, Masataka Shibamoto, N. Shinichi Takahashi

Proceedings Volume 6655, 66551L (2007) https://doi.org/10.1117/12.732784

KEYWORDS: Mirrors, Resonators, Optical pumping, Semiconductor lasers, Organic semiconductors, Reflectivity, Nitrogen, Silica, Metals, Organic materials

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Last year, we succeeded in reproducibly producing optically pumped edge-emitting organic semiconductor lasers using a low-temperature cleaving technique. Since the organic layer was generally soft and weak, its edge was damaged by the conventional cleaving at room temperature. This damage reduces the reflectance at the mirror edge and increases the threshold excitation energy. Stiffening the organic layer in liquid nitrogen enabled us to produce high-quality resonators with sufficient reproducibility. Slab waveguide devices consisting of Alq₃:DCM film (5% DCM) were vacuum-deposited onto a polished GaAs (100) substrate coated with an 1-μm-thick layer of RF (radio-frequency) sputtered SiO₂. The cleaved samples were optically pumped by a N₂ gas laser (wavelength: 337 nm) resulting in a pulse width of 600 ps at repetition rate of 20 Hz. The laser oscillation was checked by measuring the full width at half maximum of the output spectrum and its polarization characteristics. The threshold density was typically 3 μJ/cm² in a sample with a 5-mm-long resonator. We investigated the relationship between the resonator loss and the threshold density by varying the resonator length. The internal loss α and the gain coefficient β were found to be about 10.5 cm^-1 and 3.2 μJ^-1.cm, respectively. The threshold density was calculated as a function of the thickness of the emitting layer and compared with experimental values. We found that the optimum thickness is approximately 150 nm. Moreover, the reflectance at the mirror edge was increased by attaching a metal (aluminum) reflector to one side, resulting in a reduction in the threshold.

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