Polarization-Shaped Pulses

Pulse Shaping

We have extending the development of our single-mask amplitude-and-phase shaper to shape two orthogonal polarizations independently. Initially we used a compact, folded design with common-optic and near-common-paths for both polarizations to minimize mechanical and air-current fluctuations. A Walloston polarizer was imaged into a high-dispersion, low-loss Si Brewster-cut prism as the dispersive element to map the spectra of orthogonal polarizations onto separate area of the SLM.

Fig. 1. Physical layout of the folded polarization shaper.

In a subsequent implementation, a custom-designed birefringent prism made of LiNbO₃ (United Crystals) served as both the polarization splitting and dispersive element. Since our SLM shapes only the p polarization, a half-wave plate flipped the s polarization so it could be shaped. A delay plate in the other arm re-times the polarizations upon exiting the shaper. We applied a custom anti-reflection coating (OptoSigma) to yield a transmissions of T > 65% through the shaper for both polarizations.

Fig. 2. Schematic of polarization shaper. The polarization splitting of a Wollaston prism is imaged into the Si Brewster-prism of a standard folded 4f shaper.

Pulse Characterization

In order to characterize the resulting polarization-shaped pulses, we have developed a method called tomographic ultrafast retrieval of transverse light E-fields (TURTLE) in collaboration with Prof. Rick Trebino at Georgia Institute of Technology.

Fig. 3. TURTLE reconstruction of polarization-shaped pulse. (a) and (b) show FROG reconstructions of x and y field components. (c) and (d) show the TURTLE fits to FROG traces measured at ±45°. (e) and (f) show the retrieved and simulated pulse fields in time. In the "phantom" traces (a)-(d), the left and right half planes show, respectively, the measured and reconstructed FROG distributions.

We developed two approaches for polarization measurements:

• An analytic calculation to establish the polarization state from any measurement technique that yields intensity and phase
• A fitting algorithm that exploits the additional information in a FROG trace to obtain robust retrievals under laboratory conditions.

References

• L. Xu, P. Schlup, O. Masihzadeh, R. A. Bartels and R. Trebino, "Analysis of the measurement of polarization-shaped ultrashort laser pulses by tomographic ultrafast retrieval of transverse light E-fields (TURTLE)," submitted to J. Opt. Soc. Am. B (2009).
• P. Schlup, O. Masihzadeh, L. Xu, R. Trebino, and R. A. Bartels, "Tomographic retrieval of the polarization state of an ultrafast pulse," submitted to Opt. Lett. (2007).