2017 Fiscal Year Research-status Report
アキシコンを用いた共振器内コヒーレントビーム結合技術開発と応用
| Project/Area Number |
16K04986
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| Research Institution | Institute for Laser Technology |
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Principal Investigator |
コスロービアン ハイク 公益財団法人レーザー技術総合研究所, レーザーバイオ化学研究チーム, 副主任研究員 (70291036)
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | axicon lens / corner-cube reflector / retro-reflector (RR) / RR resonator / passive CBC |
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| Outline of Annual Research Achievements |
In this fiscal year, experimental and theoretical studies of the laser resonator using a reflective axicon lens (AL) with 90 degrees apex angle as a high-reflective element in the resonator were performed. The resonator stability conditions were determined by calculations. A laser based on cryogenic Yb:YAG TRAM with exchangeable high reflection elements; (a) flat mirror (Fabri-Perot (FP) resonator) and (b) AL retro-reflector, were designed and constructed.
The output power efficiency vs. the pump power, near- and far field intensity profiles, were monitored and analyzed. Experimental results for both resonator cases have been compared. In contrast to FP resonator output, from AL resonator a donut-like flattop intensity profile was obtained. The laser threshold and the slope efficiencies were estimated to be 235 W/cm2 and 0.5, and 470 W/cm2 and 0.4, for FP and AL resonators, respectively. From AL resonator, ~ 24 W output power at 90 W absorbed power was obtained. It was shown that at moderate pump powers thermal effects hardly affect the main features of the beam intensity profiles. However, at higher pump powers the system was unstable.
Marked increase of the laser threshold for AL resonator is explained by the small beam diameter (~ 1.8 mm), incurring fractionally large losses due to the scattering on the tip of the AL.
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| Current Status of Research Progress |
Current Status of Research Progress
3: Progress in research has been slightly delayed.
Reason
We have planned measuring the beam quality (M2) and the wavefront error of the AL resonator output at high pump/output powers, however, the cryogenic laser system was not stable enough (due to LN2 pool cooling).
We intend doing these comparative measurements at ambient temperature laser system which will be constructed during the final year of the project.
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| Strategy for Future Research Activity |
During this fiscal year ambient temperature laser system will be built with exchangeable FP, CCR and AL high reflective elements. Comparative experiments will be carried out. Beam quality (M2) and wavefront error measurements will be done. Polarization state of the laser beam for all three resonators will be evaluated. Different output couplers will be tried to maximize the laser output power efficiency.
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| Causes of Carryover |
We have used some equipment already present at our laboratory. The remaining amount will be used during the next fiscal year for purchasing several output couplers to maximize the laser efficiency.
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