(a) Schematic of the DIH microscope. A 500 μs pulse of 635 nm light triggered from the laser diode (LD) passes through a single mode optical fiber (F) which is coupled to a GRIN lens (L). An approximately spherical wave originating at the lens focus passes through the cuvette (C) and is incident on the sensor (S). (b) An example of a normalized hologram. (c) Three dimensional view of the imaging volume with centroid locations of 110 algae from the hologram in (b). The intersection of two regions sets the shape of the imaging volume (shaded): the region where the signal-to-background is sufficient after maximum intensity normalization and the projection of the sensor to the focal point of the GRIN lens.

(a) Histogram of normalized maximum intensities for C. reinhardtii. [(b)–(d)] Reconstructed intensities for Tetrahymena thermophila, Chlamydomonas reihardtii, and Escherichia coli (left to right). The scale bars are 40, 5, and 5 μm. Contrasts are adjusted to show detail.

(a) Dynamics of replicate populations of C. reinhardtii, nine replicates in rich medium. Upper panel: mean dynamics (line) shown with the standard deviation across replicates (gray) and the mean fluctuation within systems assuming Poisson statistics (black). The illumination was turned on at 12 h as indicated by the arrow. Middle panel: the coefficient of variation (CV) across replicates (c_vm, gray) and the mean CV assuming Poisson statistics (c_vp, black). Lower panel: the ratio c_vm∕c_vp. The straight black line denotes c_vm∕c_vp=1, where variation between systems is equal to the variation we expect from counting statistics alone. (b) Dynamics of six replicate nitrogen-deprived populations with fluctuating illumination. Panels are the same as in (a). Mean illumination is constant. Fluctuations in illumination vary across replicates from no fluctuation to 30% of the mean. Upper panel: points within the shaded region are above the calibrated maximum algal density of 10⁵∕mL. Here, densities as high as 5×10⁵ were determined from counts within in a ∼1 μL volume (Ref. ). Middle and lower panels: shaded regions indicate where c_vm,c_vp and c_vm∕c_vp were estimated from counts above the maximum calibrated density.

Spatial density profiles for C. reinhardtii. For each microscope, the imaged volume was divided into 150×150×332 μm³ bins in x, y, and z, respectively. We then sum the counts within each bin across the entire time series shown in Fig. , resulting in an average of ∼50 counts∕bin in each microscope. For each bin we compute the normalized density, the ratio of the number of counts to the number of counts we expect assuming a uniform spatial distribution (a) presents the average normalized density across systems for three planes within the imaging volume. (b)–(d) present profiles in x, y, and z, respectively, as indicated by the arrows in (a). Bars indicate bins that are included in the average. Gravity points in the −y direction. Error bars are standard error.