Tunable resonantly pumped Er:GGAG laser

The main goal of this work was to present spectroscopic and laser characteristics including the wavelength tunability of Er-doped Gd3Ga3Al2O12 (Er:GGAG) crystal. Seven Er:GGAG crystals of various Er/Gd concentrations were investigated. The maximum output peak power of 0.99 W with an absorbed pumping peak power amplitude of 5.22 W for the crystal at 0.55 at.% Er/Gd concentration was researched. The tuning was accomplished using a SiO2 birefringent plate. The laser wavelength was tunable in three eye-safe spectral bands from 1609 to 1650 nm.

Spatiotemporal beam self-cleaning for high-resolution nonlinear fluorescence imaging with multimode fiber

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibers (MMFs) has been recently reported by different research groups. Driven by the interplay between Kerr effect and beam self-imaging, BSC counteracts random mode coupling, and forces laser beams to recover a quasi-single mode profile at the output of GRIN fibers. Here we show that the associated self-induced spatiotemporal reshaping allows for improving the performances of nonlinear fluorescence (NF) microscopy and endoscopy using multimode optical fibers. We experimentally demonstrate that the beam brightness increase, induced by self-cleaning, enables two and three-photon imaging of biological samples with high spatial resolution. Temporal pulse shortening accompanying spatial beam clean-up enhances the output peak power, hence the efficiency of nonlinear imaging. We also show that spatiotemporal supercontinuum (SC) generation is well-suited for large-band NF imaging in visible and infrared domains. We substantiated our findings by multiphoton fluorescence imaging in both microscopy and endoscopy configurations.

Spatiotemporal Beam Self-cleaning for High-resolution Nonlinear Fluorescence Imaging With Multimode Fiber

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibers (MMFs) has been recently reported by different research groups. Driven by the interplay between Kerr effect and beam self-imaging, BSC counteracts random mode coupling, and forces laser beams to recover a quasi-single mode profile at the output of GRIN fibers. Here we show that the associated self-induced spatiotemporal reshaping allows for improving the performances of nonlinear fluorescence (NF) microscopy and endoscopy using multimode optical fibers. We experimentally demonstrate that the beam brightness increase, induced by self-cleaning, enables two and three-photon imaging of biological samples with high spatial resolution. Temporal pulse shortening accompanying spatial beam clean-up enhances the output peak power, hence the efficiency of nonlinear imaging. We also show that spatiotemporal supercontinuum (SC) generation is well-suited for large-band NF imaging in visible and infrared domains. We substantiated our findings by multiphoton fluorescence imaging in both microscopy and endoscopy configurations.

Spatiotemporal beam self-cleaning for high-resolution nonlinear fluorescence imaging with multimode fibres

Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibres (MMFs) has been recently reported by different research groups. Driven by the interplay between Kerr effect and beam self-imaging, BSC counteracts random mode coupling, and forces laser beams to recover a quasi-single mode profile at the output of GRIN fibres. Here we show that the associated self-induced spatiotemporal reshaping allows for improving the performances of nonlinear fluorescence microscopy and endoscopy using multimode optical fibres. We experimentally demonstrate that the beam brightness increase, induced by self-cleaning, enables two and three-photon imaging of biological samples with high spatial resolution. Temporal pulse shortening accompanying spatial beam clean-up enhances the output peak power, hence the efficiency of nonlinear imaging. We also show that spatiotemporal supercontinuum generation is well-suited for large-band nonlinear fluorescence imaging in visible and infrared domains. We substantiated our findings by multiphoton fluorescence imaging in both microscopy and endoscopy configurations.

Генерация пикосекундных импульсов лазерами с распределенной обратной связью с длиной волны 1064 nm

Picosecond optical pulses generation by 1064nm InGaAs/GaAs quantum well distributed feedback lasers was investigated. In the gain-switching regime the duration of laser pulses decreased from 150 to 35 ps with temperature increase from 5 to 50 degrees. The minimal pulses duration 35 ps and spectral width 70 pm was achieved in the optimal temperature range. The laser was placed in sealed butterfly package, which made it possible to obtain wavelength temperature tuning of 3 nm where the pulses duration was less than 45 ps. The output peak power was 0.4 W from single-mode polarization maintaining fiber.

Observation of dark and bright pulses in q-switched erbium doped fiber laser using graphene nano-platelets as saturable absorber

In this paper, a passively Q-switched Erbium doped fiber laser (EDFL) by residing Graphene nanoplatelets (GnPs) embedded in polyvinyl alcohol (PVA) based saturable absorber (SA) is demonstrated. To aid the dispersion of GNPs, a surfactant is used and then it is mixed with polyvinyl alcohol (PVA) as host polymer to develop GnPs-PVA film based passive SA. The GnPs-PVA based film then integrated in laser cavity in ring cavity configuration for pulse laser generation. The experimental works show that the proposed passive SA operates at input pump power range from 77 mW to 128 mW with a tunable repetition rate from 78.4 kHz to 114.8 kHz and a shortest pulse width of 3.69 µs. The laser produces maximum instantaneous output peak power and pulse energy of 7.3 mW and 30.46 nJ, respectively and accompanied by signal to noise ratio (SNR) of 64 dB.

Development and testing of a three-section pulse-forming network and its application to Marx circuit

A three-section pulse forming network (PFN) based on Guillemin type-C circuit was developed to meet the challenge of a compact design, high withstand voltage, and high-quality output waveform with fast rise time, flat-top duration, and 100-ns pulse width. A simplified pulse forming circuit was proposed and studied that includes only three LC-sections connected in parallel, with each section containing an inductor and a capacitor connected in series. The effect of the capacitance deviation on the output waveform was investigated. The simulation results show that when the capacitance deviation exceeds +3%, both the flat top and fall time of the output waveform of single PFN module deteriorate greatly. Fortunately, in a multi-stage PFN-Marx circuit, even if the capacitance deviation exceeds +10%, when the average capacitance of the same LC sections is close to the theoretical value, the output waveform maintains a good quality and is in good agreement with the theoretical prediction. The compact three-section PFN developed during this project has a size of only 360 mm × 342 mm × 65 mm, and a maximum withstand voltage of 120 kV. Sixteen PFN stages were assembled to form a Marx generator with design parameters to provide of an output peak power of 12 GW and a maximum peak current of 15 kA. The tested output waveform agrees well with the theoretical results, having a rise time of 31 ns, a flat-top of 104 ns, and a pulse with of 164 ns.

Design of a dual-band power combining architecture for high-power microwave applications

The remaining challenges, confronting the limited output peak power level of high-power microwave (HPM) sources, stimulate the development of power combining system. This paper reports the design methods and numerical results for a kind of dual-band incoherent power combining architecture applied in HPM. It is particularly effective to radiate dual-band microwave simultaneously, generated by a coaxial dual-band HPM source or two separate HPM sources of different bands. Two types of mode conversion structures, i.e., a dual-band feed line with co-aligned ports and a dual-band feed line with off-aligned ports, are proposed, where coaxial output port itself is adopted to connect the coaxial dual-band horn feed. These two types of feed lines provide a high conversion efficiency of about 98% from TEM or TM01mode to TE11mode and a bandwidth of about 10% at each band. The horn feed, with a high power handling capacity, is compact, and a good far-field radiation pattern at each band has been achieved by combining horizontal and vertical corrugations. Thus, the dual-band radiation system has not only realized incoherent power combination, with higher output peak power level, but also is suitable for feeding of, e.g., offset shaped single-reflector antennas in dual-band HPM systems in the future.