Amplitude and Phase Pulse Shaping

Programmable ultrafast optical pulse shapers are used in applications ranging from simple dispersion control to carefully shaped laser pulses used for coherent control of quantum dynamics. To access a complete range of temporal pulse shapes, one needs control over both spectral amplitude and phase, which has been implemented with pairs of liquid crystal spatial light modulators (LC-SLMs), acousto-optic modulators, and two-dimensional (2D) LC-SLMs, as well as acousto-optic programmable dispersion filters.

We demonstrated a new approach to phase and amplitude pulse shaping with a folded Martinez stretcher and a single, linear, high-resolution LC-SLM. In this device, the spatial mode includes a large number of SLM pixels, effectively oversampling the spatial mode, which permits spectral amplitude shaping via a high spatial-frequency sinusoidal phase grating.

In all pulse shaping devices, an accurate calibration is critical for producing predictable pulse shapes. We used an inline spectral interferometry technique to obtain a functional mapping from wavelength to pixel, and drive voltage to phase. Since the LC-SLM only shapes one polarization, two orthogonally-polarized, delayed pulses yield interference fringes from which the phase difference was extracted with a Fourier sideband filtering algorithm.

We demonstrated simultaneous control over spectral phase and amplitude by shaping the spectrum into two lobes, with a relative phase between the lobes. The spectral lobes interfere in the time-domain in a manner analogous to a double slit experiment. The figure shows Phantom-FROG traces comprising the measured FROG data (left half) with the PCGP retrieved traces (right half). The resulting pulse shape intensity profile lies within a Gaussian envelope shown as a visual guide. The intensity modulation period is set by the separation of the spectral peaks, while the temporal intensity interference structure shifts in the expected manner with the relative phase between the two spectral lobes.

References

• J. W. Wilson, P. Schlup, and R. A. Bartels, "Ultrafast phase and amplitude pulse shaping with a single, one-dimensional, high-resolution phase mask," Opt. Express 15, 8979-8987 (2007)
  http://www.opticsinfobase.org/abstract.cfm?URI=oe-15-14-8979
• P. Schlup, J. W. Wilson, K. Hartinger, and R. A. Bartels, "Dispersion balancing of variable-delay monolithic pulse splitters," Appl. Opt. 46, 5967-5973 (2007)
  http://www.opticsinfobase.org/abstract.cfm?URI=ao-46-23-5967
• The pulse shaper used is available from Boulder Nonlinear Systems