Broadband, coherent radiation in the optical frequency range is generated using micro-plasma channels in
atmospheric gases in a pump-probe experiment. A micro-plasma medium is created in a gas by a focused intense
femtosecond pump pulse. A picosecond probe pulse then interacts with this micro-plasma channel, producing broad,
coherent sidebands that are associated with luminescence lines and are red- and blue-shifted with respect to the laser
carrier frequency. These sidebands originate from the induced Rabi oscillations between pairs of excited states that
are coupled by the probe pulse. These excited states become populated in the process of plasma cooling. Thus, the
sideband radiation intensity tracks the micro-plasma evolution. The sidebands incorporate Rabi shifts corresponding
to varying value of the electric field magnitude in the probe pulse: this makes them broad and malleable to tuning.
The intensity of the probe beam ~ 10<sup>10</sup> W cm<sup>-2</sup>, creates a maximum sideband shift of > 90 meV from the carrier
frequency, resulting in an effective bandwidth of 200 meV. The sidebands may be effectively controlled by the
intensity and temporal profile of the probe pulse. The giant Rabi shift is both tunable and coherent over a wide range
of frequencies and over a wide range of atomic transitions. The fact that the coherence is observed in a micro plasma
demonstrates that Rabi cycling is possible at high temperature with moderately high laser intensities (10<sup>10</sup> W cm<sup>-2</sup>)
as long as transitions close to the driving frequency (▵ ~ 2% ωc) are available.
A new multiplexed stimulated Raman spectroscopic technique encompassing a single-shot spectral
measurement range of over 3900 cm<sup>-1</sup> is presented. Impulsive excitation of all Raman active vibrational
modes present in a medium is achieved by self-compression of a laser pulse undergoing filamentation in
air, creating coherent vibrational wave-packets. These wave-packets create a macroscopic polarization of
the medium that imparts sidebands on a delayed narrowband probe pulse. The background-free
measurement of impulsively excited Raman modes in gas-phase N<sub>2</sub>, O<sub>2</sub>, H<sub>2</sub>, CO<sub>2</sub>, toluene, ammonia, and
chloroform with a spectral resolution of 25 cm<sup>-1</sup> is presented.
We have studied the application of the diffusion mapping technique to dimensionality reduction and clustering in
multidimensional optical datasets. The combinational (input-output) data were obtained by sampling search spaces
related to optimization of a nonlinear physical process, short-pulse second harmonic generation. The diffusion mapping
technique hierarchically reduces the dimensionality of the data set and unifies the statistics of input (the pulse shape) and
output (the integral output intensity) parameters. The information content of the emerging clustered pattern can be
optimized by modifying the parameters of the mapping procedure. The low-dimensional pattern captures essential
features of the nonlinear process, based on a finite sampling set. In particular, the apparently parabolic two-dimensional
projection of this pattern exhibits regular evolution with the increase of higher-intensity data in the sampling set. The
basic shape of the pattern and the evolution are relatively insensitive to the size of the sampling set, as well as to the
details of the mapping procedure. Moreover, the experimental data sets and the sets produced numerically on the basis of
a theoretical model are mapped into patterns of remarkable similarity (as quantified by the similarity of the related
quadratic-form coefficients). The diffusion mapping method is robust and capable of predicting higher-intensity points
from a set of low-intensity points. With these attractive features, diffusion mapping stands poised to become a helpful
statistical tool for preprocessing analysis of vast and multidimensional combinational optical datasets.
Our analysis of spectral behavior of time-variant optical characteristics caused by RBC aggregation is applied to issues
of non-invasive blood monitoring. Modulations of blood flow cause the change in geometry of RBC aggregates and corresponding variance of light scattering. This changes cause the variation of optical transmission, reflection, and polarization of outcoming light. The last can be translated back in absorption coefficients of various blood constituents, refractive index mismatch, etc. For instance, in case of long occlusion simultaneous measurements of both the azimuthal angle and the ellipticity of outcoming light can provide sufficient data to determine the blood glucose.