CC BY
6The 30th International Conference on Advanced Laser Technologies LM-I-18
ALT'23
Structured optothermal traps
A. Mayorova, S. Kotova, N. Losevsky, S. Samagin, E Razueva
Lebedev Physical Institute, Samara Branch, 221, Novo-Sadovaya, Samara, 443011, Russian Federation
Optothermal traps are an actively developing manipulation technique [1]. In such traps, a sharply focused laser beam not only creates optical power, but also forms a temperature gradient and, accordingly, convection currents, due to which the capture and movement of microobjects occurs. The advantages of optothermal traps are the ability to use lower laser radiation powers (from tenths to several tens of milliwatts) compared to optical traps and to effectively capture objects of various morphologies, shapes, and sizes (from nanometers to tens of micrometers) from relatively large distances.
The authors of [2] for the first time formed a structured optothermal trap in the shape of a light ring. We implemented optothermal traps of more complex shapes: triangle and square boundaries, Archimedes spiral, double contours, lattices of zeros, including those with a vortex component [3, 4]. The report demonstrates the capabilities of structured optothermal traps for the formation of various configurations of micron and submicron objects, their dynamic rearrangement and fixing objects on a substrate.
The scheme of the experimental setup included a DPSS laser with a wavelength of 0.53 ^m, a spatial light modulator (SLM) HOLOEYE PLUTO-2-NIR-011, which forms a structured light beam. A microobjective (40x) focused the beam into a given plane, forming a structured (vortex) optical trap. The total observation power in the working area ranged from 10 mW to 100 mW. The convection component of the trap was formed by using an OC 13 light filter absorbing at a wavelength of 0.53 ^m as the bottom of the cell with samples. As manipulation microobjects, we used latex microparticles from 2 to 6 ^m, submicron silver particles, and yeast cells suspended in distilled water.
The capture of micro- and nano-objects in determined configurations, the movement of micro-objects along the boundaries of the light contour were demonstrated. It was found that the angular velocity of particles along light boundary of optothermal traps is significantly higher than in optical traps. SLM provides the ability to change the configuration of the generated intensity distributions in a given plane in real time due to the rapid replacement of one phase mask supplied to the modulator for another. In this way, the configurations of captured ensembles of particles can also be rearranged. We also proposed a simple efficient method for fixing micro- and nanoobjects in a given configuration at the bottom of a cell by adding albumin to the cell with samples and briefly increasing the laser power. Typical power values were 60-130 mW depending on albumin concentration. The technique may be of interest for fixing objects of biological origin.
[1] P. Kollipara, Z. Chen, Y. Zheng, Optical Manipulation Heats up: Present and Future of Optothermal Manipulation, ACS nano, 17(8), pp. 70517063, (2023).
[2] E. Flores-Flores, S. Torres-Hurtado, R. Páez, U. Ruiz, G. Beltrán-Pérez, S. Neale, ... and R. Ramos-García, Trapping and manipulation of microparticles using laser-induced convection currents and photophoresis, Biomedical optics express, 6(10), 4079-4087, (2015).
[3] S. Kotova, A. Korobtsov, N. Losevsky, A. Mayorova and S. Samagin, Manipulation of microparticles using combined optical traps, Journal of Quantitative Spectroscopy and Radiative Transfer, 268, pp. 107641, (2021).
[4] S. Kotova, N. Losevsky, A. Mayorova, Y. Razueva, and S. Samagin, Structured Optothermal Traps, Bulletin of the Russian Academy of Sciences: Physics, 86(12), pp. 1434-1437, (2022).
