Boulder Nonlinear Systems’ (BNS) spatial light modulator (SLM) technology can be used to shape ultrafast laser pulses spectrally and temporally in both amplitude and phase.


Why shape femtosecond laser pulses?
Ultrashort pulses are routinely used to excite dynamic processes in quantum-mechanical systems. The shape of the temporal intensity envelope plays a large role in the excitation dynamics and hence the outcome of the process. The ability to “coherently control” or drive an experiment with a shaped optical field is one of the most intriguing applications in the field of ultrafast phenomena today. Similar concepts are currently used to provide excitation state dynamics in ultrafast spectroscopy and novel sources of contrast in nonlinear microscopy. However, even if coherent control isn’t the goal, there are pragmatic reasons to consider programmable pulse shape control when using femtosecond lasers. A pulse shaper provides the ultimate control in terms of dispersion and amplitude compensation. The pulse shaper can be used to ensure that the pulse delivered on target is precisely the desired pulse, i.e., it can effectively pre-compensate for dispersive optics. This dynamic compensation ability is especially useful if the optical dispersion changes during the experiment, as it can in multiphoton microscopy when changing objective lenses, for example.

Because the LC SLM is reflective, the achromat is used off-axis to achieve a height change between the input (unshaped) pulse and the output (shaped) pulse. Thus the shaped pulse comes out of the apparatus on the same line it entered (orange line), but it is roughly 2 cm lower.
Typical ultrashort laser pulse shaper layout. The spectrum is angularly dispersed and focused to a central focal plane. A modulator placed at this plane can now operate on the amplitude and phase of individual frequencies of the light pulse.

BNS has extensive experience in developing liquid crystal SLMs for use as the dynamic element in ultrashort pulse shaping systems. For ultrashort pulse shaping, BNS can develop linear array SLMs with tens of thousands pixels with large phase stroke and highly reflective coatings for high throughput. Such large linear arrays not only increase the accuracy of the phase mask but also enable amplitude modulation in addition to phase modulation. This amplitude modulation is possible because each frequency of light is over-sampled on the modulator, meaning there are multiple pixels modulating each of the focused frequencies. Thus the SLM can be used to create localized phase gratings to diffract selected frequencies out of the beam path, thereby providing simultaneous modulation of both amplitude and phase with a single device. Currently, BNS is actively pursuing development of new SLM backplanes, novel addressing schemes, and low latency 16-bit PCIe drivers to improve the temporal response of linear array SLMs to below 1 ms for improved dynamic pulse shaping.

For more information, please read publications on our Beam and Pulse Shaping applications.
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