We propose a novel and simple technique to generate self-imaged optical bottle beam by interfering two
zeroth-order Bessel beams produced from two axicons with different wedge angle. The bottle size and the
bottle numbers can easily be adjusted by changing axicon's wedge angle. This technique shows much
efficient in beam energy conversion compared to annular slit and much high optical damaged threshold
compared to spatial light modulation. Experimental results match closely with the theoretical analysis and
numerical simulation.
Based on the generalized Huygens-Fresnel diffraction integral theory and the stationary-phase method, we analyze the influence on diffraction-free beam patterns of an elliptical manufacture error in an axicon. The numerical simulation is compared with the beam patterns photographed by using a CCD camera. Theoretical simulation and experimental results indicate that the intensity of the central spot decreases with increasing elliptical manufacture defect and propagation distance. Meanwhile, the bright rings around the central spot are gradually split into four or more symmetrical bright spots. The experimental results fit the theoretical simulation very well.
A colliding enhance resonator (CER) was used in a passively Q-switched Nd:YAG laser. Cr4+:YAG crystal and color centered LiF:F2- crystal were selected as Q-switched elements. A high energy and high stability single Q-switched pulse was obtained. Energy stability is as high as 99% which is comparable to an actively Q-switched laser. Output energy has increased 40~60% compared to a conventional resonator (CR) Q-switched laser at the same condition. Numerical calculation has shown the excellent agreement with experimental result.
Second harmonic energy conversion efficiencies in KTP and BBO crystals have been investigated by using pico-second pulse. For extracavity-doubled, conversion efficiencies 43.8% and 32% were obtained, respectively. In intracavity-doubled, efficiencies 53.4% and 70% by using convex-ARR (Anti-resonant Ring) unstable resonator, 60.2% and 80.6% by using unstable confocal resonator were achieved, respectively. It shows that KTP crystal has higher conversion efficiency at lower intensity (under KTP gray-tracking threshold) and lower efficiency at high power laser compared to the BBO crystal. This result principally caused by the KTP gray-tracking phenomena.
An Anti-Resonant Ring (ARR) structure was introduced to a conventional passively solid-state Q-switched Nd:YAG laser for the first time. Using a plane-ARR critical resonator, and Cr4+:YAG crystal, BDN dye film and color centered LiF:F-2 crystal as saturable absorber. High energy and high stability single Q-switched pulse with the output energies range from 101.6 - 82.5 mJ and stabilities range from 99.2 - 98.6% were obtained respectively. The experimental results were analyzed well by using the mechanism of the transient grating effect generated by ARR structure.
Intracavity frequency doubling with (beta) -BaB2O4 (BBO) crystal in a passively mode-locked unstable confocal resonator Nd:YAP (Nd:YALO3) pulsed laser is described. Without any amplification and pulse selection, a powerful quasi-single psec pulse at 0.54 micrometer with an energy greater than 20 mJ and power density 5 GW/cm2 was obtained by totally passive mode locking for the first time. Energy conversion efficiency 81% from 1.08 to 0.54 micrometer was achieved. The technique of intracavity second harmonic generation (ISHG) leads to stable output energy of SHG with an energy stability of 95.96%. This has a higher stability than that of fundamental wave with an energy stability of 92.78%.
A CPM, Nd:YAP (and YAG) pulsed laser with an ARR-convex unstable resonator is designed. It combines the advantages of both CPM configuration for narrow pulsewidth and unstable resonator for high output energy. This ideal fundamental wave source delivers a single pulse train with energy several tens of mJ, pulsewidth 10 Psec, and energy fluctuation < 2%. Using intracavity frequency doubling and choosing KTP, BBO and LBO as SH generator, a powerful and efficient SHG at green is generated with SH energy > 48 mJ, power density > 5 GW/cm2 and conversion efficiency as high as 50 - 70%. The theoretical analysis tallies with the experimental results.
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