Proposing a novel scheme for optical manipulation of objects using interference of two laser beams of different wavelengths

Abstract

In this paper a novel scheme for optical manipulation of objects utilizing the frequency difference of two separate lasers is proposed. In this scheme interference fringes moving at constant speed generated from two counter-propagating laser beams are expected to transport small particles trapped. For this purpose a highly stable light source is needed. On the other hand, actuators are nowadays widely used for controlling the position of or moving an object. Among them, piezoelectric actuators are commonly utilized to accurately control the angle of a diffraction grating in an external cavity laser diode (ECLD). However, conventional use of piezoelectric actuators in ECLDs causes difficulty in continuous scanning of the wavelength of an ECLD. Here, the 'tandem ECLD' utilizing an electromagnetically-driven actuator instead of a piezoelectric actuator is proposed based on the theoretical calculation that, when two separate lasers with different wavelengths sharing a common perturbation term are combined, the wavelength of the combined laser can be controlled in terms of the frequency difference of the two lasers. The wavelength shift of a prototype of the 'tandem ECLD' with respect to the current applied to the electromagnetically-driven actuator is measured. It is shown that the wavelength tuning method of an laser diode (LD) using an electromagnetically-driven actuator at low voltage exhibits equivalent performance (2.51nm wavelength shift when 2.58mA applied) to the conventional method that causes wavelength tunability using a piezoelectric actuator.