An optical sectioning programmable array microscope implemented with a digital micromirror device

The defining feature of a programmable array microscope (PAM) is the presen ce of a spatial light modulator in the image plane, A spatial light modulat or used singly or as a matched pair for both illumination and detection can be used to generate an optical section, Under most conditions, the basic o ptical properties of an optically sectioning PAM are similar to those of ro tating Nipkow discs. The method of pattern generation, however, is fundamen tally different and allows arbitrary illumination patterns to be generated under programmable control, and sectioning strategies to be changed rapidly in response to specific experimental conditions. Mie report the features o f a PAM incorporating a digital micromirror device, including the axial sec tioning response to fluorescent thin films and the imaging of biological sp ecimens. Three axial sectioning strategies were compared: line scans, dot l attice scans and pseudo-random sequence scans. The three strategies varied widely in light throughput, sectioning strength and robustness when used on real biological samples. The axial response to thin fluorescent films demo nstrated a consistent decrease in the full width at half maximum (FWHM), ac companied by an increase in offset, as the unit cells defining the patterns grew smaller. Experimental axial response curves represent the sum of the response from a given point of illumination and cross-talk from neighbourin g points, Cross-talk is minimized in the plane of best focus and when measu red together with the single point response produces a decrease in FWHM, In patterns having constant throughput, there appears to be tradeoff between the FWHM and the size of the offset. The PAM was compared to a confocal las er scanning microscope using biological samples. The PAM demonstrated highe r signal levels and dynamic range despite a shorter acquisition time. It al so revealed more structures in x-z sections and less intensity drop-off wit h scanning depth.