  Exposure to laser light alters cell culture examination via optical
microscopic imaging techniques, also based on label-free coherent digital
holography. To mitigate this detrimental feature, researchers tend to use a
broader spectrum and lower intensity of illumination, which can decrease the
quality of holographic imaging due to lower resolution and higher noise. We
study the lensless digital holographic microscopy (LDHM) ability to operate in
the low photon budget (LPB) regime to enable imaging of unimpaired live cells
with minimized sample interaction. Low-cost off-the-shelf components are used,
promoting the usability of such a straightforward approach. We show that
recording data in the LPB regime (down to 7 uW of illumination power) does not
limit the contrast nor resolution of the hologram phase and amplitude
reconstruction compared to the regular illumination. The LPB generates hardware
camera shot noise, however, to be effectively minimized via numerical
denoising. The ability to obtain high-quality, high-resolution optical complex
field reconstruction was confirmed using the USAF 1951 amplitude sample, phase
resolution test target, and finally, live glial restricted progenitor cells (as
a challenging strongly absorbing and scattering biomedical sample). The
proposed approach based on severely limiting the photon budget in lensless
holographic microscopy method can open new avenues in high-throughout (optimal
resolution, large field-of-view and high signal-to-noise-ratio single-hologram
reconstruction) cell culture imaging with minimized sample interaction.
