Laser Induced Light-Force Interaction in the Optical Near-Field Region

Laser light can induce many effects on the vicinity of the sample surface due to the proximity effects, such as the field enhancement at the surface of a small conducting particle; plasma exchange effect between the metallic tip and substrate surface. We have observed a new optical tip-sample interaction: laser induced force as the results of light pressure in the near-field region. Under the side illumination of a laser light, an additional attractive force was observed between a dielectric tip and various samples of C₆₀, optical glass, YBa₂Cu₃O_7-d(YBCO) thin film. No such effect was observed in metallic samples. This optical binding force is due to the multiple scattering of light between two close objects. The results are in good agreement with the recent theoretical calculation. The effects of the optical refraction index, thermal expansion of probe tip due to laser radiation are discussed.