Optical trapping with superfocused high-M2 laser diode beam
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Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of 'interference' superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with highprecision direct laser writing. Using axicons with apex angle 1400 and rounded tip area as small as similar to 10 μm diameter, we demonstrate 2-4 μm diameter focused laser ` needle' beams with approximately 20 mu m propagation length generated from multimode diode laser with beam propagation parameter M2= 18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ∼11 μm that could be achieved if focused by an 'ideal' lens of unity numerical aperture. The same technique using a 1600 axicon allowed us to demonstrate few-μm-wide laser 'needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.
Sokolovskii , G S , Dudelev , V V , Melissinaki , V , Losev , S N , Sobolev , K K , Deryagin , A G , Kuchinskii , V I , Farsari , M , Sibbett , W & Rafailov , E U 2015 , Optical trapping with superfocused high-M 2 laser diode beam . in AV Kudryashov , AH Paxton , VS Ilchenko , L Aschke & K Washio (eds) , Laser Resonators, Microresonators, and Beam Control XVII . Proceedings of SPIE , vol. 9343 , SPIE , Bellingham , Conference on Laser Resonators, Microresonators, and Beam Control XVII , Canada , 9/02/15 . https://doi.org/10.1117/12.2078957conference
Laser Resonators, Microresonators, and Beam Control XVII
Sokolovskii, G. S., Dudelev, V. V., Melissinaki, V., Losev, S. N., Sobolev, K. K., Deryagin, A. G., Kuchinskii, V. I., Farsari, M., Sibbett, W., & Rafailov, E. U., "Optical trapping with superfocused high-M2 laser diode beam," Laser Resonators, Microresonators, and Beam Control XVII, Kudryashov, A. V., Paxton, A. H., Ilchenko, V. S., Aschke, L., & Washio, K. (Eds.), Proceedings of SPIE 9343 (2015) Copyright 2015 Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited. http://dx.doi.org/10.1117/12.2078957.
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