Chenan Xia

Mid-infrared supercontinuum generation to 4.5 μm in ZBLAN fluoride fibers by nanosecond diode pumping

A mid-infrared supercontinuum (SC) is generated in ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF...) fluoride fibers from amplified nanosecond laser diode pulses with a continuous spectrum from approximately 0.8 microm to beyond 4.5 microm. The SC has an average power of approximately 23 mW, a pump-to-SC power conversion efficiency exceeding 50%, and a spectral power density of approximately -20 dBm/nm over a large fraction of the spectrum. The SC generation is initiated by the breakup of nanosecond laser diode pulses into femtosecond pulses through modulation instability, and the spectrum is then broadened primarily through fiber nonlinearities in approximately 2-7 m lengths of ZBLAN fiber. The SC long-wavelength edge is consistent with the intrinsic ZBLAN material absorption.

10.5 W Time-Averaged Power Mid-IR Supercontinuum Generation Extending Beyond 4

A novel, all-fiber-integrated supercontinuum (SC) laser is demonstrated and provides up to 10.5 W time-averaged power with a continuous spectrum from ~0.8 to 4 mum. The SC is generated in a combination of standard single-mode fibers and ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fluoride fibers pumped by a laser-diode-based cladding-pumped fiber amplifier system. The output SC pulse pattern can be modulated by directly modulating the seed laser diode. Near-diffraction-limited beam qualities are maintained over the entire SC spectrum. The SC average power is also linearly scalable by varying the input pump power and pulse repetition rate. We further investigate the theoretical limitations on the achievable average power handling and spectral width for the SC generation in ZBLAN fibers. Based on the thermal modeling, the standard ZBLAN fiber can handle a time-averaged power up to ~15 W, which can be further scaled up to ~40 W with a proper thermal coating applied onto the ZBLAN fiber. The SC long-wavelength edge is limited by the nonlinear wavelength generation processes, fiber bend-induced loss, and glass material loss. By using a ZBLAN fiber with a 0.3 numerical aperture, the SC spectrum could extend out to ~4.5 mum, which is then limited by the material loss.

\mu

Mid-infrared supercontinuum (SC) extending to ~4.0 mum is generated with 1.3 W time-averaged power, the highest power to our knowledge, in ZBLAN (ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF...) fluoride fiber by using cladding-pumped fiber amplifiers and modulated laser diode pulses. We demonstrate the scalability of the SC average power by varying the pump pulse repetition rate while maintaining the similar peak power. Simulation results obtained by solving the generalized nonlinear Schrödinger equation show that the long wavelength edge of the SC is primarily determined by the peak pump power in the ZBLAN fiber.

m With Direct Pulse Pattern Modulation

Third order cascaded Raman shifting is used to generate light to 1867 nm in sulfide fibers, and the nonlinearity is measured to be ~5.7 times 10-12 (m/W). Damage at ~1 GW/cm2 limits the wavelength shift range.

Power scalable mid-infrared supercontinuum generation in ZBLAN fluoride fibers with up to 1.3 watts time-averaged power

Supercontinuum (SC) with a continuous spectrum from ~0.8-3 mum is generated in a standard single-mode fiber followed by high-nonlinearity fiber. The SC is pumped by 2-ns laser diode (LD) pulses amplified in a multistage fiber amplifier, and the two octave spanning continuum is achieved by optimizing a two-stage process that separates pulse breakup and soliton formation from spectral broadening. We also demonstrate scalability of the average power in the continuum from 27 mW to 5.3 W by increasing the pulse repetition rate from 5 kHz to 1 MHz, while maintaining comparable peak power. We attribute the generated SC spectrum to the ensemble average of multiple solitons and the superposition of their corresponding spectra. The hypothesis is confirmed through simulation results obtained by solving the generalized nonlinear Schrodinger equation (NLSE). Similar SC spectra can also be obtained by using both femtosecond and nanosecond pump pulses. Furthermore, by tailoring the input pulse shape, we propose and simulate the generation of the entire SC spectrum in one single soliton under quasi-continuous-wave (CW) pulse pumping scheme.

Third order cascaded Raman wavelength shifting in chalcogenide fibers and determination of Raman gain coefficient

Supercontinuum covering 0.45-1.2 mum is scaled from 250-740 mW by varying the repetition rate of a frequency doubled telecom laser diode. Efficient SC generation requires minimal non-linearity in the amplifier and fiber dispersion matched to the pump.

Supercontinuum Generation in Silica Fibers by Amplified Nanosecond Laser Diode Pulses

We identify and differentially damage lipids and proteins using wavelengths between 2.6 and 3.8 mum from a fiber-based supercontinuum (SC) laser. Absorption spectroscopy of the constituents of normal artery and atherosclerotic plaque, including adipose tissue, macrophages and foam cells, are measured by a SC laser in the mid-infrared. By using the laser light within the C-H fatty acid and cholesterol esters absorption band, we also demonstrate differential damage of lipid-rich adipose tissue without damaging the protein-rich blood vessel wall. The experiments use a novel SC laser that is all-fiber-integrated with no moving parts, covers a continuous spectrum ranging from approximately 0.8 to beyond 4.2 microm, and outputs a time-averaged power scalable up to 10.5 W.

Power adjustable visible supercontinuum generation using amplified nanosecond gain-switched laser diode

A Mid-InfraRed FIber Laser (MIRFIL) has been developed that generates super-continuum covering the spectral range from 0.8 to 4.5 microns with a time-averaged power as high as 10.5W. The MIRFIL is an all-fiber integrated laser with no moving parts and no mode-locked lasers that uses commercial off-the-shelf parts and leverages the mature telecom/fiber optics platform. The MIRFIL power can be easily scaled by changing the repetition rate and modifying the erbium-doped fiber amplifier. Some of the applications using the super-continuum laser will be described in defense, homeland security and healthcare. For example, the MIRFIL is being applied to a catheter-based medical diagnostic system to detect vulnerable plaque, which is responsible for most heart attacks resulting from hardening-of-the-arteries or atherosclerosis. More generally, the MIRFIL can be a platform for selective ablation of lipids without damaging normal protein or smooth muscle tissue.

Mid-infrared absorption spectroscopy and differential damage in vitro between lipids and proteins by an all-fiber-integrated supercontinuum laser

An all-fiber-integrated supercontinuum laser having time-averaged power scalable up to 10.5W with diffraction limited beam quality is demonstrated. The SC pulses can be generated with arbitrary modulation patterns having on/off durations as short as 10µS.

Mid-IR super-continuum generation

Using a two-stage design with ~1 m standard fiber followed by 10 cm of high-nonlinearity, fused silica fiber, super-continuum is generated from ~0.8 to 3.0 mum using amplified 2 ns laser diode pulses.