A short-pulse Yb-doped fiber laser based on a master oscillator and power amplifier scheme is reported to yield an average power exceeding 500 W and pulse energy over 1 mJ. The final amplifier stage features a polarization-maintaining, large mode area tapered fiber with core/cladding diameters of 35/250 μm and 56/400 μm at each end of the flared section. The latter yields excellent optical conversion efficiency, near diffraction-limited output, narrow spectral linewidth and high polarization extinction ratio. The threshold for the onset of stimulated Raman scattering was further investigated using a pulsed seeder with ps-ns digitally programmable waveforms. Besides, no indication for transverse mode instability could be observed below the stimulated Raman scattering threshold, as beam quality M2 was measured < 1.3 and no fluctuations were further detected from photodiode time-traces of near-field laser beam samples.
An endoscope capable of Coherent Anti-Stokes Raman scattering (CARS) imaging would be of significant clinical value
for improving early detection of endoluminal cancers. However, developing this technology is challenging for many
reasons. First, nonlinear imaging techniques such as CARS are single point measurements thus requiring fast scanning in
a small footprint if video rate is to be achieved. Moreover, the intrinsic nonlinearity of this modality imposes several
technical constraints and limitations, mainly related to pulse and beam distortions that occur within the optical fiber and
the focusing objective.
Here, we describe the design and report modeling results of a new CARS endoscope. The miniature microscope
objective design and its anticipated performance are presented, along with its compatibility with a new spiral scanningfiber
imaging technology developed at the University of Washington. This technology has ideal attributes for clinical
use, with its small footprint, adjustable field-of-view and high spatial-resolution. This compact hybrid fiber-based
endoscopic CARS imaging design is anticipated to have a wide clinical applicability.
An analysis of the optical signal transmitted by a polarimetric sensor developed for the measurement of velocities of fluids in a capillary optical fiber is presented. It allows one to determine whether a fluid is moving in the vapor or the liquid phase.
This paper reports on a novel pair of microlens arrays (MLA's) for efficient coupling of the high aspect ratio optical beam emitted by high-power laser diode linear arrays (also referred to as laser diode bars) into the core of multimode optical fibers. These novel MLA's overcome the limitations observed when using high fill factors laser diode bars. The MLA designs are described. Results from modelling work show good coupling performances for laser diode bars with fill factors up to 75%. The technique for fabricating the complex surface profiles of the MLA's is discussed. Masters are first fabricated and MLA's are then replicated, so that volume production at low cost can be envisioned. The fabricated MLA's have been used for reshaping and fiber coupling the output of a 10-mm laser diode bar. An efficiency of 74% has been obtained when coupling into an optical fiber having a core diameter of 400 μm and a numerical aperture of 0.22.