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. Author manuscript; available in PMC: 2014 Aug 14.
Published in final edited form as: Microsc Microanal. 2008 Dec;14(6):526–531. doi: 10.1017/S1431927608080811

Figure 3.

Figure 3

Improvements in S/N using photon counting imaging of dendritic spines. Comparison of signal variations between digital (i.e., photon counting) and analog detection schemes. A,C: SHG images of dendritic spines under investigation, where arrow heads indicate target points from where SHG signals were collected for comparison. B: Signal obtained using photon counter with counting gate frequency of 2 kHz. D: Analog signal from PMT with data acquisition rate of 2 kHz and low-pass filtered at 1 kHz. Laser was on target from time t = 20 ms to t = 50 ms controlled by modulating Pockel’s cell. Coefficient of variation during the laser on period is 13% for B and 29% for D. Note the large fluctuations of signal baseline from analog detection. Scale bars: 2 μm.