Temperature measurement of single evaporating water droplets in a nitrogen flow using spontaneous Raman scattering.

The evaporation dynamics of stationary water droplets held within an electrodynamic trap are investigated in a nitrogen flow of variable velocity. In particular, the influence of the nitrogen gas flow on the temperature of the evaporating water droplets is studied. By applying a contact free measurement technique, based on spontaneous Raman scattering, time averaged and time resolved measurements of temperature in the droplet volume are compared. This technique determines the temperature from an intensity ratio in the OH stretching band of the Stokes-Raman scattering after calibration. The measured trends in temperature over the first 5 s of evaporation are found to be in agreement with theoretical calculations of the heat and mass transfer rates.

Measurement of the enhanced evanescent fields of integrated waveguides for optical near-field sensing.

The sensitivity of an integrated optical sensing device can be enhanced by coating it with a high refractive index layer, while both incoupled intensity and spatial resolution are maintained. The potential for enhanced sensing is demonstrated using titanium indiffused waveguiding structures in LiNbO(3) coated with a TiO(2) film. To the best of our knowledge, it could be measured for the first time that the outcoupled intensity at the surface was enhanced by a factor of 12-15 while keeping the penetration depth of the evanescent field constant of the order of only a few tens of nanometers. The evanescent fields of the guided modes were measured and characterized with a scanning near-field optical microscope and are in accordance with the numerical simulations.

Time integrated detection of femtosecond laser pulses scattered by small droplets.

Scattering of femtosecond laser pulses by small droplets has been measured and compared with predictions, yielding some interesting new applications for time integrated detection of the scattered field. The scattering intensity of integrated detection becomes monotonic with droplet size over large regions of scattering angle and morphology dependent resonances are surpressed, opening the way for particle sizing using the scattered intensity. Furthermore, the ripple structure no longer appears in the rainbow region of scattering, simplifying rainbow refractometry significantly. These scattering proporties of femtosecond laser pulses have been demonstrated in the laboratory using a novel Paul trap for levitating single droplets.

Optical detection of the Casimir force between macroscopic objects.

We report the optical detection of mechanical deformation of a macroscopic object induced by the Casimir force. An adaptive holographic interferometer based on a photorefractive BaTiO3:Co crystal was used to measure periodical nonlinear deformations of a thin pellicle caused by an oscillating Casimir force. A reasonable agreement between the experimental and calculated values of the first and second harmonics of the Casimir force oscillations has been obtained.

Precise subnanometer control of the position of a macro object by light pressure.

For the first time to the authors' knowledge, efficient control of the position of a macro object by coherent light was demonstrated. The minimal controllable mechanical displacement induced by the light pressure was 9 pm. No dependence of light pressure on wavelength in a broad wavelength range (405-1560 nm) was observed, as predicted by Maxwell's theory.

Refractive-index measurement of gases with a phase-shift keyed interferometer.

The presented new type of interferometer combines the principle of two-beam interferometry and the technique of phase-shift keying of holographic gratings. On the basis of the phase-shift keying technique, the interferometer employs two different geometries for the recording and the readout process. Two holographic Bragg gratings are recorded in transmission geometry and simultaneously read out in reflection geometry using a tunable IR laser. Both gratings have the same grating period but a relative phase shift. The wavelength of the readout beam is fitted to the Bragg condition for the gratings. Using a tunable IR laser for the readout process, we can measure the spectral transfer function of both combined gratings. The shape of the measured transfer function is extremely sensitive to the phase shift between the two gratings. We demonstrate an application of this method by the measurement of refractive-index variations of gases due to pressure changes of the gases. The achieved resolution with respect to the measurement of phase shifts is approximately 1/40 pi. We present experimental investigations on two kinds of gas (an inert gas and a gas composition) as well as an efficient numerical approach to simulate the transfer function for Bragg gratings with a phase shift. Furthermore, we present a method to increase the resolution based on the controlled manipulation of the transfer function.

3D integral imaging using diffractive Fresnel lens arrays.

We present experimental results with binary amplitude Fresnel lens arrays and binary phase Fresnel lens arrays used to implement integral imaging systems. Their optical performance is compared with high quality refractive microlens arrays and pinhole arrays in terms of image quality, color distortion and contrast. Additionally, we show the first experimental results of lens arrays with different focal lengths in integral imaging, and discuss their ability to simultaneously increase both the depth of focus and the field of view.

Effective spherical aberration compensation by use of a nematic liquid-crystal device.

The next generation of optical data storage system beyond DVDs will use blue laser light and an objective lens with a high numerical aperture of 0.85 to increase storage capacity. Such high numerical aperture systems have an inherent higher sensitivity to aberrations. In particular, the spherical aberration caused by cover layer thickness tolerances and--more obvious--by dual-layer disks with a typical separation of approximately 20 microm between the two layers must be compensated. We propose a novel transmissive nematic liquid-crystal device, which is capable of compensating spherical aberration that occurs during the operation of optical pickup systems.

Generation of doughnut laser beams by use of a liquid-crystal cell with a conversion efficiency near 100%.

We present a novel technique for producing a doughnut laser beam by use of a liquid-crystal cell. It is demonstrated that the liquid-crystal cell exhibits an efficiency in energy conversion near 100%. One of the main advantages of this method is its capability of dynamic switching between a Gaussian mode and a doughnut mode of different topological charges. The liquid-crystal cell is also dynamically tunable over the visible and near-infrared wavelength range. These advantages make the device appealing for laser trapping methods used in single-molecule biomechanics and for optical guiding of cold atoms.