Research Index / Ultrafast Optics
Faculty: John Nees - Theodore Norris - Gérard Mourou
Recent Graduate Students: Hsiao-Hua Liu - Seung-Whan Bahk
Past Researchers: Zenghu Chang - Haiwen Wang - Dongfeng Liu
These past years has been quite productive in the domain of Ultrafast Optics. We have concentrated efforts on the development of several essential technologies associated with generating and manipulating short and ultrashort pulses. The value of both spatial and temporal phase control is that the focused intensity generated by existing laser systems can doubled or even tripled without the addition of pump lasers, larger compression gratings and the associated system upgrades. This offers not only higher intensity but also cleaner data for any system.
Detailed control of wavefront with high-numerical-aperture optics - Using deformable mirror technology we have developed a refined capability to maintain single-micron focus in a variety of circumstances. In applications requiring a tight focus over a large volume, we have used deformable membrane technology to make an adaptable (or ‘smart’) microscope. This system ‘learns’ the corrections for the aberrations of an off-axis paraboloid and modifies the approaching wavefront to compensate with the appropriate wavefront for a given voxel. This advance at once limits the loss of light off axis and provides a wider field of view.
The more conventional deformable-plate technology has been applied to correct for aberration and distortions of focus in a vacuum system. This enables the generation of relativistic intensities (mid 1018 W/cm2) with single-millijoule energies. In either of these systems, the use of wavefront correction reduces the need for a larger more expensive laser.
Phase measurement in real time - Just as wavefront correction is crucial to the efficient generation of high focused intensity, so is temporal phase control. In order to accomplish phase control on a day-to-day basis it is important to be able to read the phase of a pulse. This has been accomplished in the past by use of methods that require an iterative algorithm to reconstruct the temporal structure of the electric field. In order to achieve immediate feedback of the temporal phase we have adopted Spectral Phase Interferometry for Direct Electric field Reconstruction (SPIDER). This is designed to read the phase of pulses from 30 fs to 5 fs. Arbitrary phase control: In addition to the use of real time phase measurement we have also made preliminary tests of a phase control system offering much greater flexibility than previous deformable mirror systems. The ‘Dazzeler’ utilizes acousto-optic diffraction to generate temporal phase changes in a pulse, allowing programmable control of temporal phase without pixelization effects.
Amplification in high-saturation-fluence materials - Owing to the relationship between emission cross-section, lifetime and bandwidth, the storage capability of high saturation-fluence materials makes them prime candidates for a new generation of high peak power lasers. We have pursued ytterbium-doped materials in the interest of demonstrating efficient directly diode-pumped chirped pulse amplification. While our first efforts in this endeavor have involved Yb-glass, we have now begun exploration of various crystalline materials. Yb-doped gadolinium-doped calcium oxy-borate (Yb:GdCOB) is a promising material for such high peak power lasers. We have been the first to demonstrate regenerative amplification in this class of materials. This experiment yielded 12 mJ per pulse with a compressed pulse-duration of 350 fs. For this work a flashlamp-pumped Ti:Sapphire laser was used to simulate laser diode pumping conditions.
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