A.S. van de Nes

Calculation of the vectorial field distribution in a stratified focal region of a high numerical aperture imaging system

We present an algorithm for calculating the field distribution in the focal region of stratified media which is fast and easy to implement. Using this algorithm we study the effect on the electric field distribution of an air gap separating a solid immersion lens and a sample, where we analyse the maximum distance for out-of-contact operation. Also, we study how the presence of a metallic substrate affects the field distribution in the focal region; the interference effects of the reflected field could be used as an alternative for 4Pi-microscopy.

Self-pulsations in vertical-cavity semiconductor lasers

We report the observation of strong self-pulsations in oxide-confined vertical-cavity surface-emitting lasers. From optical spectra and intensity noise spectra, we deduce that the pulses are strongly chirped.

Polarization-resolved linewidth-power product of a vertical-cavity semiconductor laser

We have studied the linewidth around threshold of the lasing and nonlasing polarization mode (x and y) in a TEM00 oxide-confined vertical-cavity semiconductor laser (VCSEL). We experimentally demonstrate: (i) that the nonlasing mode shows surprising behavior when the lasing mode passes through threshold, and (ii) that the polarization fluctuations in a VCSEL are limited by the same quantum noise that sets its finite Schawlow–Townes linewidth.

On the conservation of fundamental optical quantities in non-paraxial imaging systems

We discuss the application of the general conservation laws for a set of electromagnetic quantities to a non-paraxial imaging system. When paraxial Gauss–Laguerre functions are used as input functions for the optical imaging system, it is shown that the response in the image space can be expressed in terms of a limited set of the non-paraxial Gauss–Laguerre eigenmodes. Conservation of energy, linear momentum and angular momentum are numerically checked for imaging systems with a geometrical numerical aperture as high as unity.

Terahertz near-field measurements of field enhancement near metal objects

We present THz near-field measurements and calculations of the electric field around metal objects with sizes comparable to the wavelength. Several examples are presented, such as the fields of one metal sphere, and of several spheres. We show how the near-field depends on the THz polarization and frequency and on the distance between the spheres. Our results are compared with Mie theory describing the scattering of light by particles. The enhancements of the field due to a sphere are compared with those generated by a metal tip used for near-field imaging.

The use of orbital angular momentum in optical data storage

The information capacity of an optical disc is commonly increased by decreasing the diffraction unit lambda/NA of the optical read-out system (NA is the numerical aperture of the objective). We present a method to increase the information capacity at a specific lambda/NA-value by imparting orbital angular momentum to the read-out beam via specially structured optical effects

Feedback effects at stable and unstable resonant external cavity lengths

External feedback applied to a high-power semiconductor laser is found to be responsible for a drop in output power and an increased noise-level when the optical external cavity length is an integral multiple of the optical internal cavity length. The power drops and extra noise originates from a scan of the quasi-single-mode laser over its internal cavity modes, caused by a lack of interferometric stability. In the case of interferometric stability, the wavelength of the laser exhibits a staircase-like dependence on the external cavity length. All experimental results can be described by a simple rate equation model.