Simultaneous stimulated Raman gain and loss detection (SRGAL)

The fidelity of stimulated Raman scattering (SRS) microscopy images is impaired by artifacts such as thermal lensing, cross-phase modulation and multi-photon absorption. These artifacts affect differently the stimulated Raman loss (SRL) and stimulated Raman gain (SRG) channels making SRL and SRG image comparisons attractive to identify and correct SRS image artifacts. To provide answer to the question: "Can I trust my SRS images?", we designed a novel, but straightforward SRS scheme that enables the dectection of the stimulated Raman gain and loss (SRGAL) simultaneously at the same pixel level. As an advantage over the conventional SRS imaging scheme, SRGAL doubles the SRS signal by acquiring both SRL as well as SRG and allows for the identification of SRS artifacts and their reduction via a balanced summation of the SRL and SRG images.

Background-suppressed SRS fingerprint imaging with a fully integrated system using a single optical parametric oscillator

Stimulated Raman Scattering (SRS) imaging can be hampered by non-resonant parasitic signals that lead to imaging artifacts and eventually overwhelm the Raman signal of interest. Stimulated Raman gain opposite loss detection (SRGOLD) is a three-beam excitation scheme capable of suppressing this nonlinear background while enhancing the resonant Raman signal. We present here a compact electro-optical system for SRGOLD excitation which conveniently exploits the idler beam generated by an optical parametric oscillator (OPO). We demonstrate its successful application for background suppressed SRS imaging in the fingerprint region. This system constitutes a simple and valuable add-on for standard coherent Raman laser sources since it enables flexible excitation and background suppression in SRS imaging.

Dual-focus stimulated Raman scattering microscopy: a concept for multi-focus scaling

High-speed imaging is of the utmost importance for video-rate live cell investigations or to study extended sample areas at sufficient spatial resolution within reasonable time scales. Improving the speed of single-focus stimulated Raman scattering (SRS) microscopy is ultimately restricted by the sample's damage threshold and the shot noise of the demodulated laser source. To overcome this limitation, we present a dual-focus SRS approach modulating the pump laser for each focus at a distinct frequency. The corresponding probe beams are detected each by a photodiode and demodulated individually by two separate lock-in units to avoid inter-focal cross-talk. Two laterally or axially displaced images as well as hyperspectral SRS images can be obtained simultaneously within the field of view of the objective lens. The modular implementation presented here can be extended to multiple foci by using multi-channel acousto-optics modulators in combination with multi-channel lock-in amplifiers.

High-resolution multimodal flexible coherent Raman endoscope

Coherent Raman scattering microscopy is a fast, label-free, and chemically specific imaging technique that shows high potential for future in vivo optical histology. However, the imaging depth in tissues is limited to the sub-millimeter range because of absorption and scattering. Realization of coherent Raman imaging using a fiber endoscope system is a crucial step towards imaging deep inside living tissues and providing information that is inaccessible with current microscopy tools. Until now, the development of coherent Raman endoscopy has been hampered by several issues, mainly related to the fiber delivery of the excitation pulses and signal collection. Here, we present a flexible, compact, coherent Raman, and multimodal nonlinear endoscope (4.2 mm outer diameter, 71 mm rigid length) based on a resonantly scanned hollow-core Kagomé-lattice double-clad fiber. The fiber design enables distortion-less, background-free delivery of femtosecond excitation pulses and back-collection of nonlinear signals through the same fiber. Sub-micrometer spatial resolution over a large field of view is obtained by combination of a miniature objective lens with a silica microsphere lens inserted into the fiber core. We demonstrate high-resolution, high-contrast coherent anti-Stokes Raman scattering, and second harmonic generation endoscopic imaging of biological tissues over a field of view of 320 µm at a rate of 0.8 frames per second. These results pave the way for intraoperative label-free imaging applied to real-time histopathology diagnosis and surgery guidance.

Origin and suppression of parasitic signals in Kagomé lattice hollow core fibers used for SRS microscopy and endoscopy

Hollow core fibers are considered as promising candidates to deliver intense temporally overlapping picosecond pulses in applications such as stimulated Raman scattering (SRS) microscopy and endoscopy because of their inherent low nonlinearity compared to solid-core silica fibers. Here we demonstrate that, contrary to prior assumptions, parasitic signals are generated in Kagomé lattice hollow core fibers. We identify the origin of the parasitic signals as an interplay between the Kerr nonlinearity of air and frequency-dependent fiber losses. Importantly, we identify the special cases of experimental parameters that are free from parasitic signals, making hollow core fibers ideal candidates for noise-free SRS microscopy and endoscopy.

A rare case of palatin tonsillar metastasis from small cell lung cancer

Tonsillar metastases are absolutely rare. Small cell lung cancer (SCLC) is known to be the most frequent histological type of tonsillar metastases, however the way of tumor cells spreading to tonsil remains controversial. We described a case report of 76-year-old man with SCLC and tonsillar metastases, to highlight the importance of oral cavity evaluation as a part of a clinical exam and to show the rare tumor cells spreading.