Single-pass Configuration Research Articles

All-optical pulse bursts generation from a nonlinear amplifying loop mirror.

A novel method for the generation of bursts of optical pulses is proposed. It is shown analytically that a nonlinear amplifying loop mirror in single pass configuration can transform a low power input pulse into a burst consisting of pulses with individual energy up to tens of nJ. The burst features; number of pulses; and their peak power, energy, and duration can be tuned and controlled. Numerical simulations show robustness of the technique to presence of Raman scattering and that sub-picosecond pulse duration can be achieved. The latter highlights the relevance of the proposed pulse bursts generator for material processing and in medical applications involving optical ablation.

Waveguide-coupled single collective excitation of atomic arrays.

Considerable efforts have been recently devoted to combining ultracold atoms and nanophotonic devices1-4 to obtain not only better scalability and figures of merit than in free-space implementations, but also new paradigms for atom-photon interactions5. Dielectric waveguides offer a promising platform for such integration because they enable tight transverse confinement of the propagating light, strong photon-atom coupling in single-pass configurations and potentially long-range atom-atom interactions mediated by the guided photons. However, the preparation of non-classical quantum states in such atom-waveguide interfaces has not yet been realized. Here, by using arrays of individual caesium atoms trapped along an optical nanofibre6,7, we observe a single collective atomic excitation8,9 coupled to a nanoscale waveguide. The stored collective entangled state can be efficiently read out with an external laser pulse, leading to on-demand emission of a single photon into the guided mode. We characterize the emitted single photon via the suppression of the two-photon component and confirm the single character of the atomic excitation, which can be retrieved with an efficiency of about 25%. Our results demonstrate a capability that is essential for the emerging field of waveguide quantum electrodynamics, with applications to quantum networking, quantum nonlinear optics and quantum many-body physics10,11.

The effect of 980 nm and 1480 nm pumping on the performance of newly Hafnium Bismuth Erbium-doped fiber amplifier

An experimental study on the comparison of optical amplifying performance between 980 nm and 1480 nm pumping for the newly Hafnium Bismuth Erbium co-doped fiber (HB-EDF) has been presented. A short length of 1-meter HB-EDF was used as the gain medium of the optical amplifier. 1480 nm pumping is found to provide higher attainable gain and lower noise figure compared to 980 nm pumping. At 1480 nm pumping, the average small signal gain for HB-EDFA in the single pass configuration has improved by 13.4 dB in the C-band region range from 1525 nm to 1565 nm. In the double-pass configuration, a maximum small signal gain of 36.6 dB was achieved at the wavelength of 1560 nm, this is 11.6 dB higher compared to the HB-EDFA with 980 nm pumping. The double pass HB-EDFA with 1480 nm pumping has exhibited a reduction of average noise figure by 23.4% and 29.8% for -30 dBm and -10 dBm of input signal power respectively in the C- and L-band region.

2.7 W diffraction-limited yellow lasers by efficient frequency doubling of high-brightness tapered diode lasers

Abstract Modulated yellow lasers may enable more efficient photocoagulation for treatments of ophthalmic diseases. In this regard, we present a laser system emitting 2.7 W of true-yellow light at 576 nm by frequency doubling the emission of a tapered diode laser emitting 7 W at 1153 nm. The frequency doubling is based on a single-pass configuration using a cascade of two 40-mm periodically poled lithium niobate (PPLN) crystals. The stabilization of the yellow power over 10 h showed a standard deviation of 0.10% and a relative intensity noise of 0.032% rms. Moreover, we demonstrate the generation of yellow pulses with 900 mW of amplitude and a high extinction ratio in the microsecond and millisecond regimes, as required for photocoagulation.

Watt-level green random laser at 532 nm by SHG of a Yb-doped fiber laser.

We have developed a watt-level random laser at 532nm. The laser is based on a 1064nm random distributed ytterbium (Yb) gain-assisted fiber laser seed with a 0.35nm linewidth and 900mW polarized output power. A study for the optimal length of the random distributed mirror was carried out. A Yb-doped fiber master oscillator power amplifier architecture is used to amplify the random seeder laser without additional spectral broadening up to 20W. By using a periodically poled lithium niobate crystal in a single-pass configuration, we generate in excess of 1W random laser at 532nm by second-harmonic generation (SHG) with an efficiency of 9%. The green random laser exhibits an instability <1%, an optical signal-to-noise ratio >70 dB, a 0.1nm linewidth, and excellent beam quality.

Anti‐Stokes cooling of Yb-doped KYF4 single crystals

Truly vibration-free, optical cooling of solids, relying on annihilation of lattice phonons via anti-Stokes fluorescence, is a rapidly advancing technology with a huge potential impact on a variety of space and terrestrial applications. In this paper, we focus on investigation of active media and we report on the first observation of anti-Stokes cooling in a novel material, a Yb-doped KYF4 single-crystal, promising in relation to its multi-site structure and low phonon cut-off energy. The cooling efficiency of the sample was measured, external quantum efficiency and background absorption were evaluated and compared to other fluoride active media. Bulk cooling by ~ 1.8 °C was observed under ~ 1.5 W laser excitation, tuned close to 1025 nm, in single-pass configuration.

0.83 W, single-pass, 1.54 μm gas Raman source generated in a CH4-filled hollow-core fiber operating at atmospheric pressure.

We report here the first watt-level efficient single-pass 1.54 μm fiber gas Raman source by methane-filled hollow-core fiber operating at atmospheric pressure. Pumped with a high-power MOPA (master oscillator power amplifier) structure Q-switched 1.06 μm pulsed solid-state laser, efficient 1.54 μm Stokes wave is generated in a single-pass configuration by vibrational stimulated Raman scattering of methane molecules. With an experimentally optimized fiber length of 3.2 m, we get a 1543.9 nm Stokes wave operating at atmospheric pressure with a record average power of ~0.83 W, which is about 12 times higher than the similar experiment previously reported, and the corresponding power conversion efficiency is about 45%. Operating at atmospheric pressure makes it more convenient in future applications.

High efficiency single-pass SHG of low power CWML and QML laser in an MgO:PPLN

We present the second harmonic generation (SHG) of a low power and of both Q-switched mode-locked (QML) and CW (CWML) mode-locked picosecond (ps) laser at 1064 nm based on a single-pass frequency-doubling configuration of an end-pumped passively mode-locked Nd:YVO4 laser in a 3-mm periodically poled MgO-doped lithium-niobate (MgO:PPLN). The maximum SHG conversion efficiency is 27.4% when the laser is operated in the QML mode at an averaged pumping power of 895 mW and the conversion efficiency is reduced to 24.1% in the CWML mode with a maximum averaged pumping power of 1.37 W. The corresponding pulse width of the SHG output is estimated to be 15.5 ps. The repetition rates of the laser are 137 kHz for QML and 78.7 MHz for CWML. The theoretical efficiencies of SHG are calculated in both QML and CWML and the results agree very well with the experiments especially in the QML. This work provides a useful method for efficient frequency conversion for low power mode-locked lasers.

Engineering the spectral and temporal properties of a GHz-bandwidth heralded single-photon source interfaced with an on-demand, broadband quantum memory

Photonics offers a route to fast and distributed quantum computing in ambient conditions, provided that photon sources and logic gates can be operated deterministically. Quantum memories, capable of storing and re-emitting photons on demand, enable quasi-deterministic operations by synchronizing stochastic events. Interfaced source–memory systems are thus a key building block in photonics-based quantum information processors. We discuss the design of the single-photon source in this type of light–matter interface and present an experimental system based on a Raman-type quantum memory. In addition to the spectral purity of the produced heralded single photons, we find that their temporal distinguishability also becomes important due to the implicit temporal binning derived from photon storage in the memory. When aiming to operate the source–memory system at high repetition rates, a practical compromise between both of these requirements needs to be found. Our implemented photon source system demonstrates such a solution and enables passive stability, high brightness in a single-pass configuration, high purity as well as good mode matching to our Raman memory.

Continuous-Wave Mid-Infrared Gas Fiber Lasers

Efficient continuous-wave laser emission of acetylene molecules at 3.1 μ m wavelength has been demonstrated in low-loss hollow-core fiber by optically pumping using a fiber-amplified diode laser around 1.53 μ m. In this paper, we report and compare the continuous-wave laser performance of acetylene molecules in the cavity and single-pass configurations. The use of low-loss antiresonant hollow-core fiber makes the single-pass configuration ideal for high-power laser generation and enables over 1.1 W continuous-wave mid-infrared laser output with over 33% slope efficiency relative to the absorbed pump power. The systematic characterization of power-scaling and pump power absorption properties demonstrates that the molecular kinetics inside hollow-core fiber determines the laser performance, and that low fiber attenuation is key to high-efficiency continuous-wave output.

Green and continuous route to assemble lateral nanodimensional graphitic oxide composites without process interruption

Lateral nanoscaled graphitic oxide composite flakes were assembled in a single-pass configuration without process interruption, and the assembled flakes demonstrated controlled drug release having magneto- and photothermal activities as well as contrasting properties.

A novel single-pass reverse osmosis configuration for high-purity water production and low energy consumption in seawater desalination

Seawater reverse osmosis (SWRO) desalination is required to produce high-quality water to meet stricter water standards, which could be satisfied with single-pass RO through the advancement of reverse osmosis (RO) membranes. In this study, a novel single-pass RO configuration was proposed to further improve permeate quality. Split partial single-pass (SSP) RO is a design in which the permeate from the rear RO element(s) in a pressure vessel is blended with the RO feed. This blending resulted in the dilution of the feed, leading to the production of high-quality permeate with lower energy demand. Modeling of the RO process demonstrates that SSP RO had the highest energy efficiency when the permeate from the 7th element (i.e., the last one in the single pass RO configuration) was circulated back and mixed with the feed. For typical SWRO operating conditions, SSP RO was effectively able to improve permeate quality. In fact, SSP RO produced an approximately 15% purer permeate compared to conventional single-pass RO. SSP RO was also always more energy-efficient than the two-pass RO configurations. The economic feasibility of the design was assessed further and the possibility of its practical application explored.

Modulation instability in dispersion oscillating fibers

In this review we present recent theoretical and experimental progress on modulation instability and parametric amplification processes in dispersion oscillating fibers. These optical fibers are characterized by longitudinal periodic variations of their outer diameter engineered over the meter-long scale, which provides an additional degree of freedom to the system and leads to the generation of multiple MI sideband pairs. The main results published in single-pass configurations and in passive cavities are summarized in this review.

Photoinduced Rapid Transformation from Au Nanoagglomerates to Drug-Conjugated Au Nanovesicles.

Gold (Au) agglomerates (AGs) are reassembled using Triton X‐100 (T) and doxorubicin (D) dissolved in ethanol under 185 nm photoirradiation to form TAuD nanovesicles (NVs) under ambient gas flow conditions. The positively charged Au particles are then electrostatically conjugated with the anionic chains of TD components via a flowing drop (FD) reaction. Photoirradiation of the droplets in a tubular reactor continues the photophysicochemical reactions, resulting in the reassembly of Au AGs and TD into TAuD NVs. The fabricated NVs are electrostatically collected onto a polished aluminum rod in a single‐pass configuration. The dispersion of NVs is employed for bioassays to confirm uptake by cells and accumulation in tumors. The chemo‐photothermal activity is determined both in vitro and in vivo. Different combinations of components are also used to fabricate NVs using the FD reaction, and these NVs are suitable for gene delivery as well. This newly designed gaseous single‐pass process results in the reassembly of Au AGs for incorporation with TD without the need of batch wet chemical reactions, modifications, separations, or purifications. Thus, this process offers an efficient platform for preparing biofunctional Au nanostructures that requires neither complex physicochemical steps nor special storage techniques.

Sub-50 ps pulses at 620 nm obtained from frequency doubled 1240 nm diamond Raman laser.

We report a monolithic 1240 nm diamond Raman laser producing pulses with duration of 42-62 ps at 100 kHz repetition rate, and maximum average power of 246 mW. The Raman laser is formed by a 0.5-mm thick planar diamond, coated on both sides and pumped by ~100 ps pulses from a Q-switched 1064 nm laser. The maximum conversion efficiency from 1064 nm to 1240 nm was about 25%. The 1240 nm signal was frequency-doubled in single-pass configuration through a 10-mm long LBO crystal, enabling generation of pulses with a duration of 29-46 ps at 620 nm. The maximum average power at 620 nm was 128 mW, and the maximum conversion efficiency from 1240 nm to 620 nm was 50%. The Raman laser provides an efficient and flexible way to extend short pulse operation to wavelengths in spectral domains difficult to reach, such as 620 nm and in addition provides a simple pulse shortening mechanisms.

Mid-infrared 1 W hollow-core fiber gas laser source.

We report the characteristics of a 1W hollow-core fiber gas laser emitting CW in the mid-IR. Our system is based on an acetylene-filled hollow-core optical fiber guiding with low losses at both the pump and laser wavelengths and operating in the single-pass amplified spontaneous emission regime. Through systematic characterization of the pump absorption and output power dependence on gas pressure, fiber length, and pump intensity, we determine that the reduction of pump absorption at high pump flux and the degradation of gain performance at high gas pressure necessitate the use of increased gain fiber length for efficient lasing at higher powers. Low fiber attenuation is therefore key to efficient high-power laser operation. We demonstrate 1.1W output power at a 3.1μm wavelength by using a high-power erbium-doped fiber amplifier pump in a single-pass configuration, approximately 400 times higher CW output power than in the ring cavity previously reported.

Performance of 1.73 μm Superluminescent Source Based on Bismuth-Doped Fiber Under Various Temperature Conditions and γ-Irradiation

Performance characteristics of superluminescent fiber source (SFS) operating at 1.73 μ m under different temperature conditions and gamma-irradiation of active fiber were studied. The SFS in a single-pass and backward pumping configuration was constructed using a bismuth-doped high-germania silicate fiber. The output parameters of the SFS including output power, spectral shape, mean wavelength, full width at half maximum, and peak position were measured in the temperature range from –60 to +60 °C. The simulation of the bismuth SFS at room temperature was performed for the first time to our knowledge. The simulation was also used for theoretical study of the SFS performance under gamma-irradiation. The obtained results of calculation are in good agreement with the experimental data. The effect of gamma-radiation exposure (60Co source) of active fiber on the SFS output power was investigated at different temperatures. The output power as a function of radiation dose is presented. No photobleaching of radiation induced absorption in bismuth doped fibers by pump light at 1550 nm was observed.

Optical parametric generation in orientation-patterned gallium phosphide.

We report an optical parametric generator (OPG) based on the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched nanosecond Nd:YAG laser at 1064nm with 25kHz pulse repetition rate, the OPG can be tuned across 1721-1850nm in the signal and 2504-2787nm in the idler. Using a 40-mm-long crystal in single-pass configuration, we have generated a total average output power of up to ∼18 mW, with ∼5 mW of idler power at 2670nm, for 2W of input pump power. The OPG exhibits a passive stability in total output power better than 0.87% rms over 1h, at a crystal temperature of 120°C, compared to 0.14% rms for the input pump. The output signal pulses, recorded at 1769nm, have duration of 5.9ns for input pump pulses of 9ns. Temperature-dependent loss measurements for the pump polarization along the [100] axis in the OP-GaP crystal have also been performed, for the first time, indicating a drop in transmission from 28.8% at 50°C to 19.4% at 160°C.

Direct fluorescent labeling for efficient biological assessment of inhalable particles

Labeling of aerosol particles with a radioactive, magnetic, or optical tracer has been employed to confirm particle localization in cell compartments, which has provided useful evidence for correlating toxic effects of inhaled particles. However, labeling requires several physicochemical steps to identify functionalities of the inner or outer surfaces of particles, and moreover, these steps can cause changes in size, surface charge, and bioactivity of the particles, resulting in misinterpretations regarding their toxic effects. This study addresses this challenging issue with a goal of introducing an efficient strategy for constantly supplying labeled aerosol particles in a single-pass configuration without any pre- or post-physicochemical batch treatments of aerosol particles. Carbon black (CB, simulating combustion-generated soot) or calcium carbonate (CC, simulating brake-wear fragments) particles were constantly produced via spark ablation or bubble bursting, respectively. These minute particles were incorporated with fluorescein isothiocyanate-poly(ethylene glycol) 2-aminoethyl ether acetic acid solution at the orifice of a collison atomizer to fabricate hybrid droplets. The droplets successively entered a diffusion dryer containing 254-nm UV irradiation; therefore, the droplets were dynamically stiffened by UV to form fluorescent probes on particles during solvent extraction in the dryer. Particle size distributions, morphologies, and surface charges before and after labeling were measured to confirm fluorescence labeling without significant changes in the properties. In vitro assays, including confocal imaging, were conducted to confirm the feasibility of the labeling approach without inducing significant differences in bioactivity compared with untreated CB or CC particles.

97-μJ single frequency linearly polarized nanosecond pulsed laser at 775 nm using frequency doubling of a high-energy fiber laser system

We report a high-energy (∼97 μJ), high-peak power (∼20 kW), single-frequency, linearly polarized, near diffraction-limited (M2<1.2) ∼4.8-ns pulsed laser source at 775 nm with a 260-Hz repetition rate. This laser was achieved by frequency doubling of a high-energy linearly polarized all-fiber-based master oscillator–power amplifier, seeded by a single-frequency semiconductor distributed feedback laser diode at 1550 nm. The frequency doubling is implemented in a single-pass configuration using a periodically poled lithium niobate crystal, and a conversion efficiency of 51.3% was achieved.