Andreas Schmitt-Sody

Precise intracavity phase interferometry in an optical parametric oscillator with two pulses per cavity round trip

Phase shifts of less than 10(-7) rad are measured through intracavity phase interferometry, a figure that corresponds to cavity length changes of the order of femtometers. The technique is demonstrated with a synchronously pumped optical parametric oscillator. By applying the technique to the measurement of the nonlinear index of refraction of lithium niobate, it is shown that higher accuracy and sensitivity than the traditional z-scan method can be achieved.

The importance of corona generation and leader formation during laser filament guided discharges in air

Images taken with an intensified CCD camera show the dynamics during filament guided discharge events. The images reveal that filament initiated corona plays a role in the presented results. Furthermore, the images show the formation of leaders, propagating and eventually bridging the gap between the high voltage (HV) electrodes. Analysis of the images and comparison to oscilloscope traces of voltage and current dynamics reveal the origin of the delay between the filament and HV discharge and allows for a probability of discharge analysis.

Control of the configuration of multiple femtosecond filaments in air by adaptive wavefront manipulation

We demonstrate the ability to position single and multiple filaments arbitrarily within the energy reservoir of a high power femtosecond laser pulse. A deformable mirror controlled by a genetic algorithm finds the optimal phase profile for producing filaments at user-defined locations within the energy reservoir to within a quarter of the nominal filament size, on average. This proof-of-principle experiment demonstrates a potential technique for fast control of the configuration of the filaments.

Third-order optical nonlinearity effect of DNA- and polyvinylpyrrolidone-functionalized carbon nanotubes

We have used single-stranded DNA (ssDNA) and polyvinylpyrrolidone (PVP) to disperse multiwalled carbon nanotubes (MWNTs) in water solution through sonication and centrifuge procedures. The advantage of these two polymers is that they do not need toxic organic solvents to distribute the carbon nanotubes. The scanning electron microscope (SEM) technique has been used to investigate the interaction between polymer molecules and MWNTs. The images show that MWNTs can be distributed effectively into the two polymer solutions. The third-order optical susceptibility, nonlinear optical absorption coefficient and optical power limiting of these dispersions have been characterized experimentally using a femtosecond laser system with a tunable range of 750–850 nm. The imaginary part of the third-order optical susceptibility has also been computed.

Implementation of a long range, distributed-volume, continuously variable turbulence generator.

We have constructed a 180-m-long distributed, continuously variable atmospheric turbulence generator to study high-power laser beam propagation. This turbulence generator operates on the principle of free convection from a heated surface placed below the entire propagation path of the beam, similar to the situation in long-distance horizontal propagation for laser communications, power beaming, or directed energy applications. The turbulence produced by this generator has been characterized through constant-temperature anemometry, as well as by the scintillation of a low-power laser beam.

Videos of light filamentation in air

Light filaments are of interest for applications in remote sensing, communications, and the control of electronic discharges. Different plasma dynamics and emitted radiation have been observed according to the initial pulse characteristics and beam collimation. To help observing and understanding these observations, a new technique of creating a movie of the moving light pulse and the plasma emission in its wake is presented. Over 1,000 synchronized frames of a streak camera are combined to produce the 4D (2 D space, time in ps and wavelength) movie.

Electric field measurements during filament-guided discharge

Abstract. One application of ultrashort pulse filamentation is the coupling of external electric fields to filament plasmas and guiding of high-voltage discharges. However, the full physics of the guiding mechanism is still in question. Several models have been presented and explanations have been suggested to capture the full physics of the discharge event. For the first time, measurements of the electric field dynamics between two electrodes during filament-guided discharges are presented here, to the best of our knowledge. The electric field dynamics show an exponential growth region, a plateau, followed by a sharp drop off coinciding with the discharge event. We believe these results will ultimately answer the questions regarding the guiding mechanism.

High-Power Hybrid Mode-Locked External Cavity Semiconductor Laser Using Tapered Amplifier with Large Tunability

We report on hybrid mode-locked laser operation of a tapered semiconductor amplifier in an external ring cavity, generating pulses as short as 0.5 ps at 88.1 MHz with an average power of 60 mW. The mode locking is achieved through a combination of a multiple quantum well saturable absorber (>10% modulation depth) and an RF current modulation. This designed laser has 20 nm tuning bandwidth in continuous wave and 10 nm tuning bandwidth in mode locking around 786 nm center wavelength at constant temperature.

Plasma Generation by Laser Filamentation in Air

Streak cameras, with high-temporal resolution, are a powerful tool to image light propagation and plasma dynamics. Here, we present the image of a 2.2-TW peak power, 50-fs laser pulse, propagating in a nonlinear fashion over a distance of 1.3 m, leaving behind plasma. A direct measurement of the Rayleigh scattering of the pulse and the plasma emission are presented here.

Generation of multiterawatt vortex laser beams

We report the fabrication of large-area phase masks on thin fused-silica substrates that are suitable for shaping multiterawatt femtosecond laser beams. We apply these phase masks for the generation of intense femtosecond optical vortices. We further quantify distortions of the vortex beam patterns that result from several common types of mask defects.