Focusing of light following a 4-fpulse shaper: Considerations for quantum control

The focusing of coherent light, modified by a spatial light modulator (SLM) based 4-f pulse shaper, is discussed in the context of scalar diffraction theory. Diffractive effects (including space-time coupling) in SLMs may alter the size and shape of a subsequent laser focus. A numerical approach is used to investigate the effects of some common phase masks on the properties of the laser focus. The extreme case of an alternating phase mask is considered in some detail, as it clearly illustrates the effects of space-time coupling. The results are compared to a simple analytic model. The potential influence of SLM diffractive effects on multiphoton quantum control studies is discussed and some approaches to minimizing undesirable diffractive effects are suggested.