Mid-infrared supercontinuum generation from 1.6 to >11 µm using concatenated step-index fluoride and chalcogenide fibers.

We demonstrate an all-fiber supercontinuum source that generates a continuous spectrum from 1.6 µm to >11 µm with 417 mW on-time average power at 33% duty cycle. By utilizing a master oscillator power amplifier pump with three amplification stages and concatenating solid core ZBLAN, arsenic sulfide, and arsenic selenide fibers, we shift 1550 nm light to ∼4.5 µm, ∼6.5 µm, and >11 µm, respectively. With 69 mW past 7.5 µm, this source provides both high power and broad spectral expansion, while outputting a single fundamental mode.

Generation of near-diffraction-limited, high-power supercontinuum from 1.57 µm to 12 µm with cascaded fluoride and chalcogenide fibers.

We generate a supercontinuum (SC) spectrum ranging from 1.57 µm to 12 µm (20 dB bandwidth) with a soft glass fiber cascade consisting of ZrF4-BaF2-LaF3-AlF3-NaF fiber, As2S3 fiber, and As2Se3 fiber pumped by a nanosecond thulium master oscillator power amplifier system. The highest on-time average power generated is 417 mW at 33% duty cycle. We observe a near-diffraction-limit beam quality across the wavelength range from 3 µm to 12 µm, even though the As2Se3 fiber is multimode below 12 µm. Our study also shows that parameters of the As2Se3 fiber, such as numerical aperture, core size, and core/cladding composition, have significant effects on the long wavelength edge of the generated SC spectrum. Our results suggest that the high numerical aperture of 0.76 and low-loss As2Se3/GeAs2Se5 core/cladding material all contribute to broad SC generation in the long-wave infrared spectral region. Also, among our results, 10 µm core diameter selenide fiber yields the best spectral expansion, while the 12 µm core diameter selenide fiber yields the highest output power.

All-optical histology using ultrashort laser pulses.

As a means to automate the three-dimensional histological analysis of brain tissue, we demonstrate the use of femtosecond laser pulses to iteratively cut and image fixed as well as fresh tissue. Cuts are accomplished with 1 to 10 microJ pulses to ablate tissue with micron precision. We show that the permeability, immunoreactivity, and optical clarity of the tissue is retained after pulsed laser cutting. Further, samples from transgenic mice that express fluorescent proteins retained their fluorescence to within microns of the cut surface. Imaging of exogenous or endogenous fluorescent labels down to 100 microm or more below the cut surface is accomplished with 0.1 to 1 nJ pulses and conventional two-photon laser scanning microscopy. In one example, labeled projection neurons within the full extent of a neocortical column were visualized with micron resolution. In a second example, the microvasculature within a block of neocortex was measured and reconstructed with micron resolution.