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We report an all-fiber free-running bidirectional dual-comb laser system for coherent anti-Stokes Raman scattering spectroscopy based on spectral focusing. The mode-locked oscillator is a bidirectional ring-cavity erbium fiber laser running at a repetition rate of$\sim <\#comment/>114\mathrm{M}\mathrm{H}\mathrm{z}$. One output of the bidirectional laser is wavelength-shifted from 1560 to 1060 nm via supercontinuum generation for use as the pump source. We have been able to record the Raman spectra of various samples such as polystyrene, olive oil, polymethyl methacrylate (PMMA), and polyethylene in the C–H stretching window. We believe that this all-fiber laser design has promising potential for coherent Raman spectroscopy and also label-free imaging for a variety of practical applications.

Imaging submicron fluorescent microspheres are the standard method for measuring resolution in multiphoton microscopy. However, when using high-energy pulsed lasers, photobleaching and heating of the solution medium may deteriorate the images, resulting in an inaccurate resolution measurement. Moreover, due to the weak higher-order response of fluorescent microspheres, measuring three-photon resolution using three-photon fluorescence (3PEF) and third-harmonic generation (THG) signals is more difficult. In this report, we demonstrate a methodology for complete characterization of multiphoton microscopes based on second- and third-harmonic generation signals from the sharp edge of GaAs wafers. This simple methodology, which we call the nonlinear knife-edge technique, provides fast and consistent lateral and axial resolution measurement with negligible photobleaching effect on semiconductor wafers. In addition, this technique provides information on the field curvature of the imaging system, and perhaps other distortions of the imaging system, adding greater capability compared to existing techniques.

We present the design and construction of an all-fiber high-power optical parametric chirped-pulse amplifier working at 1700 nm, an important wavelength for bio-photonics and medical treatments. The laser delivers 1.42 W of output average power at 1700 nm, which corresponds to ∼40 nJ pulse energy. The pulse can be de-chirped with a conventional grating pair compressor to ∼450 fs. Furthermore, the laser has a stable performance with relative intensity noise typically below the -130 dBc/Hz level for the idler pulses at 1700 nm from 10kHz to 16.95 MHz, half of the laser repetition ratef/2.

Pancreatic cancer is a common cancer with poor odds of survival for the patient, with surgical resection offering the only hope of cure. Current surgical practice is time-consuming and, due to time constraints, does not sample the whole cut surface sufficiently to check for remaining cancer. Although microscopy with hematoxylin and eosin (H&E) stain is the gold standard for microscopic evaluation, multiphoton microscopy (MPM) has emerged as an alternative tool for imaging tissue architecture and cellular morphology without labels. We explored the use of multimodal MPM for the label-free identification of normal and cancerous tissue of the pancreas in a mouse model by comparing the images to H&E microscopy. Our early studies indicate that MPM using second-harmonic generation, third-harmonic generation, and multiphoton excitation of endogenous fluorescent proteins can each contribute to the label-free analysis of the pancreatic surgical margin.

We report a self-triggered asynchronous optical sampling terahertz spectroscopy system based on a single bidirectional mode-locked fiber laser and plasmonics-enhanced photoconductive nanoantennas. The fiber laser generates two optical mutually coherent pulse trains with a stable repetition rate difference, enabling time-domain terahertz spectroscopy without using any mechanical delay line, stabilization electronics, or external trigger. The resolved terahertz spectra over a 0.1–2 THz frequency range and a 30-second measurement time show more than a 70-dB dynamic range, revealing water absorption lines matching the HITRAN database, through a light-weight and compact spectroscopy setup.