Microscopy

When coupled with narrow-band lasers, SLMs have been used to shape and selectively re-direct an excitation source to one or more sites within a sample, providing random access and multi-focal imaging capabilities. When used with broadband or supercontinuum lasers, SLMs can tune the illumination within a sample spectrally, spatially, and temporally for a variety of effects. SLMs are also frequently used to pre-correct the wavefront of an excitation source to compensate for aberrations caused by the optical system, refractive index mismatch, and scattering in turbid media, which provides improved resolution and contrast deep within tissue samples. Boulder Nonlinear Systems (BNS) SLM technology has even be used for spectral pulse shaping in nonlinear microscopy technologies, such as background-free coherent anti-Stokes Raman spectroscopy (CARS) microscopy and pump-probe techniques such as two-photon absorption microscopy. Through creative applications of these various techniques, SLMs can provide increased imaging speed, novel contrast mechanisms, and super-resolution in a variety of laser scanning microscopy modalities.

More recently, BNS has developed polarization independent SLMs that can modulate randomly polarized light, such as fluorescence emission, when placed in the imaging path. These modulators have been used to correct for aberrations in fluorescent imaging and as a non-mechanical switch that enables users to view a sample with a range of imaging modes, including brightfield, darkfield, spiral phase contrast, quantitative differential interference contrast (qDIC), or spatial light interference microscopy (SLIM).

In addition to developing novel capabilities, such as the polarization independent modulators, BNS is actively developing larger and faster SLMs with novel addressing schemes and low latency drivers, as well as bolt-on microscopy modules, to improve the capabilities of a wide-range of microscopy techniques, such as brightfield, darkfield, DIC and phase contrast, confocal, multiphoton, CARS, stimulated emission depletion (STED), spatial frequency domain imaging (SFDI), structured illumination microscopy (SIM), Fresnel incoherent correlation holography (FINCH), and many more.

Examples of narrowband CARS. From left to right: 1) Fat cells (red) surrounded by collagen (green). 2) Theophylline hydrate crystal on the surface of a tablet. 3) PMMA and PS spheres detected in consecutive measurements and overlaid. 4) Sebaceous gland showing lipid droplets inside the cells at the base of a hair. 5) Three overlaid measurements of constituents of an asthma dosage form. (Courtesy of H.L. Offerhaus and A.C.W. van Rhijn – University of Twente)

Super Resolution. Enhanced spatial resolution in the THG microscope is demonstrated through switching the polarization of the field from linear at the center, to circular at the beam edges. As the THG scattering is suppressed for circular polarization, the THG signal diameter is reduced. (Courtesy of Randy Bartels – Colorado State University)

SLiM. a) Microscope schematic with SLIM module, b) SLM generated phase rings and the corresponding images recorded by the CCD and c) SLIM quantitative phase image of a hippocampal neuron. (Courtesy of Gabriel Popescu – University of Illinois at Urbana-Champaign)