Spotlight on optics: The manipulation of the temporal shape of optical pulses has been extensively studied for a few decades, due to its importance in many practical applications including optical communications, imaging, high power laser amplification, and even laser processing. Since the temporal variation of ultrashort pulses, especially femtosecond (fs) laser pulses, is much faster than the speed of any mechanical or electrical component, it is essential to use purely optical techniques to precisely control the shape of pulse. One of the most common ways to get this job done is to control the spectral amplitude and phase of a laser pulse by using a spatial light modulator (SLM) in a 4-f configuration, given that the time and frequency domains are connected by Fourier transformation. This configuration basically allows ultrashort laser pulses to be spectrally separated by a grating, such that the phase and amplitude of different spectral components are focused and manipulated one by one at a SLM prior to their recombination at the grating.

In this paper, Schwarz et al. extend the shaping capabilities of fs laser pulses to include full-vector field control by cleverly implanting a new design in a 4-f configuration. A brief description of the authors’ method is as follows: The authors employ a train of femtosecond pulses with a pulse duration and spectral bandwidth of 61 fs and 13.6 nm, respectively. A reference beam is first separated without generating satellite pulses by using a pair of glass wedges. Next, prior to the 4-f setup, a half wave plate, a thin film polarizer, and two lenses are used to split a single fs pulse into two perpendicularly polarized fs pulses with appropriate amplitudes and angle of separation, so that two polarization components can propagate along two arms of an interferometric common-path setup within a 4-f configuration. A thin film polarizer is chosen over a Wollaston prism due to a large separation angle between two perpendicularly polarized components with no angular dispersion, and a common-path interferometer is selected for high stability. Then, the amplitude and phase of the two components are independently adjusted at a SLM in a 4-f setup, and the two components are recombined into a single pulse, where the temporal shape and polarization states of the pulse are arbitrarily controlled. Finally the single pulse is combined with the reference beam, and the two polarization components of the combined pulse are characterized independently with dual-channel Fourier transform spectral interferometry.

The authors thoroughly demonstrate the performance of their full vector-field pulse shaper by temporally shaping two perpendicularly polarized pulses individually. With this new pulse shaping technique, both the temporal shape and polarization states of ultrashort pulses can be controlled with high stability. It is therefore expected that this technique can allow the revealing of hidden features in ultrafast spectroscopy and microscopy.

---

---

 Add Comment

You must log in to add comments.