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We present a method for measuring the van der Waals force between two microspheres based on photonic force microscopy. We trapped a microsphere as probe by optical tweezers. The restricted Brownian motion of Gaussian distribution could be found in this system. The vibration center of the probe was affected by the van der Waals force when a target microsphere was closer to the probe. We measured the vibration center of the probe at different separation between the pair of microspheres. Based on this, the measurement of the van der Waals force between the two microspheres was realized with a high precision. Our method can realize the direct measurement of van der Waals force without using the variation rules of it. This method results in a simple structure, would not damage the sample, and can be suitable for the surface of any shape. It is general and has a wide range of applications in other fields of micro-force measurement.

Optical traps have been widely used in a large variety of applications ranging from biophysics to nano-sciences. More than one microscopic object can be captured in an optical trap. In the practical application, it is always necessary to distinguish and control the number of captured objects in the optical trap. In this paper, a novel method has been presented to distinguish the number of trapped microspheres by measuring the intensity of back signal. Clear descent of the back signal has been observed when a microsphere is captured in the center of optical trap. The relative coupling efficiency of back signal decreases as the number of captured microspheres increases both in experiment and theory. This method contributes to miniaturization and integration of applied systems due to getting rid of the imaging system, and is generally applicable to the area of nanoparticle trapping.

We build numerical models of dual-waveguide trap with rough and tilted endfaces using both the finite element method. The optical field distribution of waveguide trapping house with rough and tilt endfaces is simulated and analyzed. The results shows that rough endfaces cause the incident beam scattered and the tilted endfaces make incident beam refracted. According to optical field distribution, axial and transversal optical trapping forces are calculated. When endfaces roughness increase, both the axial and transversal trapping forces decrease, meaning trapping depth decreased. The transversal equilibrium positions move around unpredictably, off center. The stiffness and width of optical trap change little. When endfaces tilt angles increase, both the axial and transversal trapping forces decrease, meaning trapping depth decreased. The transversal equilibrium positions move along minus transversal axis. It is no obvious change in stiffness and width of optical trap.

A novel active optical approach for acceleration measurement based on a Y-shaped cavity dual-frequency laser is presented and demonstrated. Applied acceleration causes a change in the refractivity of sensing gas in one of the two cavities, resulting in a beat frequency variation between two orthogonal polarized lights. As a result, this approach produces a modulation of beat frequency strictly proportional to the input acceleration. Preliminary experiments with a 632.8 nm Y-shaped cavity He–Ne dual-frequency laser confirm the validity of the laser sensor. The experimental results show that the laser sensor in this approach characterizes a nearly linear response to the input acceleration, which is a projection of gravitational acceleration. The experimental values of the scale factors are mostly in good agreement with theoretical ones. By optimizing the optical and geometrical parameters of the laser sensor, an acceleration measurement resolution of 10−5–10−6 gravitational acceleration (within ±5 g measurement range) could be expected. Furthermore, we investigate the principle about the sign of the scale factor in detail, and propose a simple but efficient method to distinguish the direction of the acceleration acted on the laser sensor.

In this work, in order to analyse the magnetic field of rectangular current-carrying coil, a simulation with the magnetostatic function of the ANSOFT Maxell 3D software has been carried out. The characteristics of the magnetic field distribution have been analysed based on the results of simulation. In addition, an experiment aimed to measure the magnetic induction intensity at a point on the central axis of the rectangular coil has been designed to verify the simulation results. The results show that the error between the simulation results and the actual measurement is 1.24%, which proved the accuracy of the simulation.

A wavelength selection method by a Fabry-Perot etalon in cavity is reported, helping weak line in laser cavity emitting. Comparing with other wavelength selection methods, this method can provide better resolution of lines, more output power and need shorter length of cavity. A series of experiments are done to test the output properties of the 629nm He-Ne Laser. The wavelength selection method in He-Ne Laser by internal F-P etalon could choose the needed one from two nearby lines no matter how close they are. That makes it possible to select wavelength especially for the nearby lines with gain of sharp contrast in other Lasers.

A theory is presented for the transmission of transverse magnetic waves through a finite number of subwavelength slits in metal film. While a single slit achieves the single channel limit on resonance, multiple slits show super-transmission exceeding the single channel limit. The phenomenon of super-transmission is revealed as a result of cross-coupling of modes and confirmed by simulations. The influence of finite permittivity in the IR and microwave regime is included by perturbative corrections to the theory. The theory agrees quantitatively with past experiments and finite-difference time-domain simulations. By considering two or more modes in the slit region, our theory provides an approach to the analysis of cross-coupling among slits, which allows for super-transmission and features of a Fano resonance.