Lens-less surface second harmonic imaging

Abstract

Lens-less surface second harmonic generation imaging (SSHGI) is used to image an SHG active molecule, (S)-(+)-1,1'-bi-2-naphthol (SBN), incorporated into a lipid bilayer patterned with the 1951 United States Air Force resolution test target. Data show the coherent plane-wave nature of SHG allows direct imaging without the aid of a lens system. Lens-less SSHGI readily resolves line-widths as small as 223 μm at an object-image distance of 7.6 cm and line-widths of 397 μm at distances as far as 30 cm. Lens-less SSHGI simplifies the detection method, raises photon collection efficiency, and expands the field-of-view. These advantages allow greater throughput and make lens-less SSHGI a potentially valuable detection method for biosensors and medical diagnostics.

Second Harmonic Correlation Spectroscopy: Theory and Principles for Determining Surface Binding Kinetics

“…The coherence length was determined using lensless surface SHG imaging (SSHGI) by incorporating SBN into DOPC bilayers patterned into various sized linewidths using the United States Air Force (USAF) resolution test target. 39 The lensless SHG image of two different sized linewidths, 355 and 397 mm, is reproduced here and shown in Figure 3a. For comparison, a white light image of the same linewidths of the test target are shown in Figure 3c.…”

“…One such technique that exhibits an output with large spatial and temporal coherence is SHG. 39 SHG is an emissive coherent process where the incident beams typically have a narrow frequency distribution, such that when they are spatially and temporally overlapped in a counter-propagating fashion, produce an extremely spatially and temporally coherent emission. 39 The highly coherent emission of SHG also makes it possible to have a much larger spatially coherent illumination/detection area than DLS.…”

“…39 SHG is an emissive coherent process where the incident beams typically have a narrow frequency distribution, such that when they are spatially and temporally overlapped in a counter-propagating fashion, produce an extremely spatially and temporally coherent emission. 39 The highly coherent emission of SHG also makes it possible to have a much larger spatially coherent illumination/detection area than DLS. The authors have previously shown that the coherence area of the SHG output when using a properly configured counter-propagating geometry with a highly collimated source is essentially the illuminated area of the sample as long as the incident beams are monochromatic, collimated, and spatially and temporally coherent.…”

“…The authors have previously shown that the coherence area of the SHG output when using a properly configured counter-propagating geometry with a highly collimated source is essentially the illuminated area of the sample as long as the incident beams are monochromatic, collimated, and spatially and temporally coherent. 39 The temporal coherence of SHG has a linear relationship to the square of the spatially coherent illumination area 39 meaning the coherence length increases with increasing illumination area. The large spatial and temporal coherence eliminates the need for a pinhole aperture at the detector, which increases the signal.…”

High throughput second harmonic imaging for label-free biological applications

“…The second one is to parallelize the imaging process. Recent advancements [46] include wide-field counter propagating SHG geometries [10,11], lens-less imaging approaches [49], harmonic holography [50,51], multi-confocal imaging [52,53], and spatiotemporal wide-field illumination [54][55][56][57][58].…”