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We generate elliptically polarized harmonics with tunable handedness by controlling laser ellipticity in relativistic laser-solid interactions. Experiments closely match simulations, enabling multi-color, circularly polarized relativistic-intensity pulses, with up to 10% energy in the second harmonic. 

We present an experimental demonstration of chromatic angular dispersion of a probe beam incident on a transmission plasma grating. The results show a path towards a plasma compression grating for high intensity laser pulses. 

The primary goal of this research is to use lasers to visualize and study the density gradients and flow in gases and plasma. We compare and contrast three methods of laser imaging to measure density gradients and flow in gases and plasma: (1) shadowgraphy, (2) knife-edge schlieren, and (3) two-color interferometry. The first, being the simplest, utilizes a method to visualize the density gradients sans spatial filters or reference beams. Shadowgraphy only records the spatial second derivative or Laplacian of the refractive index field, making the method largely qualitative. The second is sensitive to density gradients, but only in one direction at a time. Lastly, two-wavelength interferometry employs one wavelength which is more sensitive in the plasma while the other is more sensitive to the neutral gas, to further study, distinguish, and quantify the refractive index changes between plasma and neutral gas. Taken together, these three techniques provide a holistic insight into the flow mechanics of plasma and gases. 

A plasma grating is generated by temporally crossing and interfering two femtosecond beams to create modulated ionization. We achieve maximum Bragg diffraction efficiency of 35% by tuning grating transverse size, length, and incident beam configurations. 

Spectral broadening of 25-fs multi-terawatt laser pulses has been achieved in low-pressure atmospheric gases without significant loss of spatial coherence in the laser beam by femtosecond laser filamentation.