will only be by a scaling factor due to the gain in the GPC LS. Alternatively, the SLM can be illuminated directly with small Gaussian beam to fit inside the active phase modulation region. However, this comes at the expense of losing some of modulation
pixels and consequently having a broader jinc PSF. Moreover, the
central hotspot can be problematic for high power applications, as
previously discussed in Section 1, which provides the motivation
for using uniform illumination. Utilizing much of the SLM pixels is
suggested for applications requiring finer resolutions and thus
highlights the importance of a properly match readout beam.
For our extended pattern targets, we use the university's logo
and a binarized version of a standard test image. Fig. 5 shows our
results for extended light patterns and there is a substantial intensity gain in the resulting holographic reconstruction of extended intensity patterns similar to the spot arrays. The presence
of speckle (not an effect by the GPC-enhanced read-out) is in
general an undesirable feature of phase-only holography but for
some applications this can be tolerated when the aim is to efficiently generate high intensities such as is the case for two-photon
fabrication [21,22].
Complex beam shaping methods may be employed to reduce
speckles however cascading SLMs or other pixel-based diffractive
modulation elements to address both amplitude and phase is inefficient due to the inherently low diffraction efficiency of SLMs and
may demand high input powers for operation. Theoretical maximum
efficiency of the first diffraction order from a phase grating addressed