RESUMEN

We investigate the optical trapping of polystyrene microspheres in optical tweezers. The transverse capture gradient forces of polystyrene microspheres with different numerical aperture are theoretically and experimentally evaluated by the power spectral density roll-off method. It is found that the trapping force of the experimental measurement is much stronger than that of the theoretical results. The discordance is attributed to the slow light effect near the focus, which has been found in recent years [Science347, 857 (2015)10.1126/science.aaa3035; Opt. Express18, 10822 (2010)10.1364/OE.18.010822; Opt. Commun.332, 164 (2014)10.1016/j.optcom.2014.06.057]. The modified trapping force of the theoretical results by considering the slow light effect near the focus is well consistent with that of the experimental results.

Asunto(s)

RESUMEN

A phase refractive index is measured directly from an unwrapped spectral phase distribution whose 2π ambiguity is determined by fitting the spectral phase distribution with functions based on Cauchy's equation. The phase refractive index of a quartz glass with 20 µm thickness is measured exactly from three spectral phase distributions detected in two different configurations of a spectrally resolved interferometer. Since there is a high possibility that the 2π ambiguity cannot be correctly determined when there is a large difference between a function of the real refractive index and Cauchy's equation, characteristics of the fitting are examined.

RESUMEN

To the best of our knowledge, at the present time there is no answer to the fundamental question stated in the title that provides a complete and satisfactory physical description of the structured nature of Hermite-Gauss beams. The purpose of this manuscript is to provide proper answers supported by a rigorous mathematical-physics framework that is physically consistent with the observed propagation of these beams under different circumstances. In the process we identify that the paraxial approximation introduces spurious effects in the solutions that are unphysical. By removing them and using the property of self-healing, that is characteristic to structured beams, we demonstrate that Hermite-Gaussian beams are constituted by the superposition of four traveling waves.

RESUMEN

In order to perform an exact surface profile measurement with a white-light scanning interferometer (WLSI), an actual optical path difference (OPD) changing with time is detected with an additional interferometer in which the light source of the WLSI and an optical band-pass filter are used. This interferometer is simply equipped in the WLSI and does not negatively influence the WLSI. The real OPD is easily calculated from an interference signal with the same signal processing as that in the WLSI. The interference signal of the WLSI is corrected with the real OPD values or the real scanning position values. The corrected interference signal with a constant sampling interval is obtained with an interpolation method. With this correction method, a surface profile with a step shape of 3-µm height is measured accurately with an error less than 2 nm.

RESUMEN

A new signal processing is proposed in which the dispersion phase is not subtracted from the detected spectral phase distribution. The linear and bias components in the spectral phase distribution are used to calculate the complex-valued interference signal (CVIS). The simulations verify that the dispersion phase generates an inclination in the measured surface profile along one direction in which the magnitude of the dispersion phase changes linearly. The simulations also show that the position of zero phase nearest the position of amplitude maximum in the CVIS almost does not change due to the bias component, although the random phase noise contained in the interference signal changes the slope of the linear component. Measured surface profiles show that the new signal processing achieves highly accurate measurement by the CVIS.

RESUMEN

Complex-valued interference signals (CVISs) of a white-light scanning interferometer (WLSI) and a spectrally resolved interferometer (SRI) are obtained from their real-valued interference signals through Fourier transform. First the phase distribution in the CVIS of the SRI indicates a dispersion phase caused by two sides of unequal length in a cubic beam splitter, and the magnitude of the dispersion phase changes linearly along a horizontal direction of the beam splitter. Next the dispersion phase with a different magnitude is subtracted from the spectral phase in Fourier transform of the CVIS of the WLSI. Through inverse Fourier transform of this spectral distribution, a dispersion-free CVIS is obtained, and the position of zero phase nearest to the position of amplitude maximum provides a surface profile measured accurately with an error less than 4 nm after 2π corrections, while a position calculated by the linear component of the spectral phase causes measurement error less than 12 nm.