Physics

Polarization Puzzle

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Science  14 Nov 2008:
Vol. 322, Issue 5904, pp. 1026
DOI: 10.1126/science.322.5904.1026a

When very high-intensity light strikes a solid surface, it can liberate multiple electrons and ions that then continue to collide rapidly with one another, forming a plasma state. These collisions in turn lead to emission across a broader spectrum of wavelengths, as kinetic and electromagnetic energy steadily interconvert. The chaos of such a process might be expected to distribute the emitted light across completely random orientations. However, Liu et al. make the surprising observation that under certain conditions, the plasma produced from a silicon (Si) surface initially emits a continuum of ultraviolet light that is >95% polarized. The optimal conditions involved focusing a pair of ultrashort laser pulses spaced 80 ps apart in time onto a Si(111) crystal face; this dual pulse sequence proved key to maximizing the effect. The degree of polarization was also highly sensitive to the distance between the surface and the laser focus, and scaled inversely with pulse intensity (at least within the range sufficient to induce plasma emission). — JSY

Appl. Phys. Lett. 93, 161502 (2008).

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