Alex A. Zozulya

Amplitude and Phase Measurements of Femtosecond Pulse Splitting in Nonlinear Dispersive Media

Frequency-resolved optical gating is used to characterize the propagation of intense femtosecond pulses in a nonlinear, dispersive medium. The combined effects of diffraction, normal dispersion, and cubic nonlinearity lead to pulse splitting. The role of the phase of the input pulse is studied. The results are compared with the predictions of a three-dimensional nonlinear Schrödinger equation.

Waveguide atom beam splitter for laser-cooled neutral atoms.

A laser-cooled neutral-atom beam from a low-velocity intense source is split into two beams while it is guided by a magnetic-field potential. We generate our multimode beam-splitter potential with two current-carrying wires upon a glass substrate combined with an external transverse bias field. The atoms are guided around curves and a beam-splitter region within a 10-cm guide length. We achieve a maximum integrated flux of 1.5x10(5)atoms/s with a current density of 5x10(4)amp/cm (2) in the 100-microm -diameter wires. The initial beam can be split into two beams with a 50/50 splitting ratio.

Transistorlike behavior of a Bose-Einstein condensate in a triple-well potential

In the last several years considerable efforts have been devoted to developing Bose-Einstein-condensate-based devices for applications such as fundamental research, precision measurements, and integrated atom optics. Such devices, capable of complex functionality, can be designed from simpler building blocks as is done in microelectronics. One of the most important components of microelectronics is a transistor. We demonstrate that a Bose-Einstein condensate in a three-well potential structure where the tunneling of atoms between two wells is controlled by the population in the third shows behavior similar to that of an electronic field-effect transistor. Namely, it exhibits switching and both absolute and differential gain. The role of quantum fluctuations is analyzed, and estimates of the switching time and parameters for the potential are presented.

Circular solitons do not exist in photorefractive media

The shape of two-dimensional solitary beams propagating in photorefractive media with an externally applied field is studied. The analytical results indicate that, for both focusing and defocusing nonlinearities, radially symmetric self-channeled beams do not exist. Some recent experiments are interpreted in light of the present results.

Characterizing the nonlinear propagation of femtosecond pulses in bulk media

Frequency-resolved optical gating is used to characterize the amplitude and phase of intense femtosecond pulses propagating in nonlinear dispersive media. The combined effects of group velocity dispersion (GVD) and third-order nonlinearity (nz) lead to rapid broadening and splitting of the pulses. We present measurements at 800 and 1200 nm and investigate the influence of the chirp of the input field. Measurements are compared with the predictions of one- and three-dimensional nonlinear Schrodinger equations. The influence of the Raman contribution to the nonlinear index of refraction is also examined theoretically.

Comparative study with double-exposure digital holographic interferometry and a Shack–Hartmann sensor to characterize transparent materials

We compare wave-front measurements using double-exposure digital holography and a Shack-Hartmann sensor. A voltage-driven liquid-crystal wedge modulates the optical wave front and provides a refractive-index gradient typical of interesting transparent materials. Measurement accuracy and reliability are similar for both methods. In our opinion, digital holographic interferometry has several advantages for both laboratory and field environments. When compared with Shack-Hartmann methods, these advantages include hardware simplicity and robustness, relative insensitivity to sample dynamic range, and less computational demanding and more straightforward data evaluation algorithms. We believe that digital holography provides the methodology of choice for field studies of transparent materials such as microgravity protein crystal growth experiments.

Dynamics of self-focused femtosecond laser pulses in the near and far fields

We investigate the propagation of femtosecond pulses in a nonlinear, dispersive medium at powers several times greater than the critical power for self focusing. The combined effects of diffraction, normal dispersion and cubic nonlinearity lead to pulse splitting. We show that detailed theoretical description of the linear propagation of the pulse from the exit face of the nonlinear medium (near field) to the measuring device (far field) is crucial for quantitative interpretation of experimental data.

Wave-function recombination instability in cold-atom interferometers

Cold-atom interferometers use guiding potentials that split the wave function of the Bose-Einstein condensate and then recombine it. We present a theoretical analysis of the wave-function recombination instability that is due to the weak nonlinearity of the condensate. It is most pronounced when the accumulated phase difference between the arms of the interferometer is close to an odd multiple of {pi} and consists in exponential amplification of the weak ground state mode by the strong first excited mode. The instability exists for both trapped-atom and beam interferometers.

Full-field characterization of femtosecond pulses after nonlinear propagation

The nonlinear Schrodinger equation is often used to model the evolution of ultrashort pulses. However, as peak powers increase and spot sizes decrease, details surrounding the propagation of femtosecond pulses become unknown. In this context, the measured amplitude and phase of the electric field on a femtosecond time scale is valuable information in the study of light-matter interactions. We use second-harmonic frequency-resolved optical gating (SHG-FROG) and spectral interferometry as tools for tracking the nonlinear propagation of intense femtosecond pulses in fused silica.

Revealing buried information: Statistical processing techniques for ultracold-gas image analysis

The techniques of principal and independent component analysis are applied to images of ultracold atoms. As an illustrative example, we present the use of these model-independent methods to rapidly determine the differential phase of a Bose-Einstein condensate interferometer from large sets of images of interference patterns. These techniques have been useful in the calibration of the experiment and in the investigation of phase randomization. The details of the algorithms are provided.