The effect of source backing materials and excitation pulse durations on laser-generated ultrasound waveforms.

In this article, it is shown experimentally that a planar laser-generated ultrasound source with a hard reflective backing will generate higher acoustic pressures than a comparable source with an acoustically matched backing when the stress confinement condition is not met. Furthermore, while the source with an acoustically matched backing will have a broader bandwidth when the laser pulse is short enough to ensure stress confinement, the bandwidths of both source types will converge as the laser pulse duration increases beyond stress confinement. The explanation of the results is supported by numerical simulations.

A QbD Approach to Design and to Optimize the Self-Emulsifying Resveratrol-Phospholipid Complex to Enhance Drug Bioavailability through Lymphatic Transport.

Objectives: Despite having profound therapeutic value, the clinical application of resveratrol is restrained due to its <1% bioavailability, arising from the extensive fast-pass effect along with enterohepatic recirculation. This study aimed to develop a self-emulsifying formulation capable of increasing the bioavailability of resveratrol via lymphatic transport. Methods: The resveratrol−phospholipid complex (RPC) was formed by the solvent evaporation method and characterized by FTIR, DSC, and XRD analyses.

High pulse energy fibre laser as an excitation source for photoacoustic tomography.

A custom fibre laser designed as an excitation source for biomedical photoacoustic tomography has been developed. It is based on a custom-drawn large core diameter fibre (200 µm) that enables high pulse energies (∼10 mJ) to be achieved. The system can provide variable pulse durations (10 - 500 ns) and pulse repetition frequencies (100 Hz - 1 kHz), as well as arbitrary pulse bursts according to specific user defined sequences.

Controllable duration and repetition-rate picosecond pulses from a high-average-power OP-GaAs OPO.

We report an orientation-patterned gallium arsenide (OP-GaAs) optical parametric oscillator (OPO) offering a high degree of temporal flexibility with controllable pulse repetition rates from 100 MHz to 1 GHz and pulse durations from ∼95 ps to ∼1.1 ns. The maximum average power of 9.

High-average-power picosecond mid-infrared OP-GaAs OPO.

We report a high-average-power mid-infrared picosecond (ps) optical parametric oscillator (OPO) based on orientation-patterned gallium arsenide (OP-GaAs), with wide wavelength tunability. The OP-GaAs OPO is synchronously pumped by a thulium-doped-fiber (TDF) master oscillator power amplifier (MOPA), seeded by a gain-switched laser diode. At a pump power of 35.

Compact, high repetition rate, 4.2 MW peak power, 1925 nm, thulium-doped fiber chirped-pulse amplification system with dissipative soliton seed laser.

We report the demonstration of a high average- and peak-power, 1925 nm, thulium-fiber based chirped pulse amplification (CPA) system. A compact, dissipative soliton thulium-fiber, mode-locked seed produced pre-chirped pulses with 25 ps duration, 45 mW output power and repetition rate of 15.7 MHz.

Ultra-short wavelength operation of thulium-doped fiber amplifiers and lasers.

We fabricate and characterize a germanium/thulium (Ge/Tm) co-doped silica fiber in order to enhance the gain at the short wavelength edge of the thulium emission band (i.e. 1620-1660 nm).

106 W, picosecond Yb-doped fiber MOPA system with a radially polarized output beam.

We report the generation of high average output power, high peak power, and high pulse energy radially polarized picosecond pulses from a compact gain-switched laser-diode-seeded Yb-doped fiber master oscillator power amplifier (MOPA) system. A q-plate was employed as a mode converter prior to the final power amplifier to efficiently convert the linearly polarized Gaussian-shaped beam into a donut-shaped radially polarized beam. The desired vector beam was efficiently amplified yielding ∼110  ps pulses with a maximum output pulse energy of ∼30.

Nonlinear dynamic of picosecond pulse propagation in atmospheric air-filled hollow core fibers.

Atmospheric air-filled hollow core (HC) fibers, representing the simplest yet reliable form of gas-filled hollow core fiber, show remarkable nonlinear properties and have several interesting applications such as pulse compression, frequency conversion and supercontinuum generation. Although the propagation of sub-picosecond and few hundred picosecond pulses are well-studied in air-filled fibers, the nonlinear response of air to pulses with a duration of a few picoseconds has interesting features that have not yet been explored fully. Here, we experimentally and theoretically study the nonlinear propagation of ~6 ps pulses in three different types of atmospheric air-filled HC fiber.

5.6 kW peak power, nanosecond pulses at 274 nm from a frequency quadrupled Yb-doped fiber MOPA.

A 2 W deep-ultraviolet (DUV) source at 274 nm with 5.6 kW peak power is demonstrated by frequency quadrupling a diode-seeded, polarization-maintaining (PM), Yb-doped fiber master oscillator power amplifier (MOPA) system delivering 1.8 ns pulses at a repetition rate of 200 kHz.

295-kW peak power picosecond pulses from a thulium-doped-fiber MOPA and the generation of watt-level >2.5-octave supercontinuum extending up to 5 μm.

We report a gain-switched diode-seeded thulium doped fiber master oscillator power amplifier (MOPA) producing up to 295-kW picosecond pulses (35 ps) at a repetition rate of 1 MHz with a good beam quality (M ~1.3). A narrow-band, grating-based filter was incorporated within the amplifier chain to restrict the accumulation of nonlinear spectral broadening and counter-pumping of a short length of large-mode-area (LMA) fiber was used in the final stage amplifier to further reduce nonlinear effects.

Highly efficient frequency doubling and quadrupling of a short-pulsed thulium fiber laser.

We report the second harmonic generation and fourth harmonic generation of the output from a short-pulsed (~ 80 ps) thulium-doped fiber laser, generating 976 and 488 nm wavelengths with high efficiency. With a narrow-linewidth (0.5 nm) pump at a power of 3.

Demonstration of arbitrary temporal shaping of picosecond pulses in a radially polarized Yb-fiber MOPA with > 10 W average power.

High precision surface processing has an unmet demand for picosecond pulses with arbitrary temporal profiles in radial polarization states and at high average powers. Here, simultaneous spatial and arbitrary temporal shaping of chirped 10 - 100 picoseconds pulses is demonstrated with an Yb-doped fiber laser system generating an output power of more than 10 W at 40 MHz repetition frequency. The closed-loop control algorithm carves the pulses using a commercial, rugged, and fiberized optical pulse shaper placed at the front end of the system and uses feedback from the output pulse shapes for optimization.

All-optical mode-group multiplexed transmission over a graded-index ring-core fiber with single radial mode.

We present a design of graded-index ring-core fiber (GI-RCF) supporting 3 linearly polarized (LP) mode-groups (i.e. LP, LP and LP) with a single radial index of one for mode-division multiplexed (MDM) transmission.

Broadband silica-based thulium doped fiber amplifier employing multi-wavelength pumping.

A multi-wavelength pumped thulium doped fiber amplifier is investigated to extend the spectral gain coverage of the amplifier in the 1.7-1.9μm wavelength range.

Generation of stretched pulses and dissipative solitons at 2 μm from an all-fiber mode-locked laser using carbon nanotube saturable absorbers.

We demonstrate for the first time, to the best of our knowledge, a thulium-doped, all-fiber, mode-locked laser using a carbon nanotube saturable absorber, operating in the dissipative-soliton regime and the stretched-pulse-soliton regime. The net dispersion of the laser cavity is adjusted by inserting different lengths of normal dispersion fiber, resulting in different mode-locking regimes. These results could serve as a foundation for the optimization of mode-locked fiber-laser cavity design at the 2 μm wavelength region.

High gain holmium-doped fibre amplifiers.

We investigate the operation of holmium-doped fibre amplifiers (HDFAs) in the 2.1 µm spectral region. For the first time we demonstrate a diode-pumped HDFA.

High-energy, near- and mid-IR picosecond pulses generated by a fiber-MOPA-pumped optical parametric generator and amplifier.

We report a high-energy picosecond optical parametric generator/amplifier (OPG/A) based on a MgO:PPLN crystal pumped by a fiber master-oscillator-power-amplifier (MOPA) employing direct amplification. An OPG tuning range of 1450-3615 nm is demonstrated with pulse energies as high as 2.6 μJ (signal) and 1.

Demonstration of ultra-low NA rare-earth doped step index fiber for applications in high power fiber lasers.

In this paper, we report the mode area scaling of a rare-earth doped step index fiber by using low numerical aperture. Numerical simulations show the possibility of achieving an effective area of ~700 um² (including bend induced effective area reduction) at a bend diameter of 32 cm from a 35 μm core fiber with a numerical aperture of 0.038.

Detailed study of four-wave mixing in Raman DFB fiber lasers.

We both experimentally and numerically studied the ultra-compact wavelength conversion by using the four-wave mixing (FWM) process in Raman distributed-feedback (R-DFB) fiber lasers. The R-DFB fiber laser is formed in a 30 cm-long commercially available Ge/Si standard optical fiber. The internal generated R-DFB signal acts as the pump wave for the FWM process and is in the normal dispersion range of the fiber.

Compact, high-pulse-energy, high-power, picosecond master oscillator power amplifier.

We report a compact, stable, gain-switched-diode-seeded master oscillator power amplifier (MOPA), employing direct amplification via conventional Yb(3+)-doped fibers, to generate picosecond pulses with energy of 17.7 μJ and 97-W average output power (excluding amplified spontaneous emission) at 5.47-MHz repetition frequency in a diffraction-limited and single-polarization beam.

Minimizing differential modal gain in cladding-pumped EDFAs supporting four and six mode groups.

We employ a Genetic Algorithm for the purpose of minimization of the maximum differential modal gain (DMG) over all the supported signal modes (at the same wavelength) of cladding-pumped four-mode and six-mode-group EDFAs. The optimal EDFA designs found through the algorithm provide less than 1 dB DMG across the C-band (1530-1565 nm) whilst achieving more than 20 dB gain per mode. We then analyze the sensitivity of the DMG to small variations from the optimal value of the erbium doping concentration and the structural parameters, and estimate the fabrication tolerance for reliable amplifier performance.

Generation of mode-locked optical pulses at 1035 nm from a fiber Bragg grating stabilized semiconductor laser diode.

We report the generation of transform-limited, ~18 ps optical pulses from a fiber Bragg grating (FBG) stabilized semiconductor laser diode. Up to 7.2 pJ of pulse energy and a peak power of 400mW were achieved when operating at a repetition frequency of 832.

200 W Diffraction limited, single-polarization, all-fiber picosecond MOPA.

A fully fiberized, single-polarization, gain-switched diode-seeded fiber master oscillator power amplifier (MOPA) system is demonstrated delivering 28 ps pulses at variable repetition frequencies ranging from 53 MHz up to 858 MHz. An average signal output power of 200 W was achieved with good OSNR for all operating frequencies. A maximum pulse energy of 3.