Low Pump Energy Research Articles

Design of a hybrid chalcogenide-glass on lithium-niobate waveguide structure for high-performance cascaded third- and second-order optical nonlinearities.

Dispersion engineering for efficient supercontinuum generation (SCG) is investigated in a hybrid nonlinear photonic platform that allows cascaded third- and second-order optical nonlinearities in transverse-electric (TE) guided modes. The highly nonlinear chalcogenide waveguides enable SCG spanning over 1.25 octaves (from about 1160nm to more than 2800nm at 20 dB below maximum power), while the TE polarization attained is compatible with efficient second-harmonic generation in a subsequent thin-film lithium niobate waveguide integrated monolithically on the same chip. A low-energy pump pulsed laser source of only 25pJ with 250fs duration, centered at a wavelength of 1550nm, can achieve such wideband SCG. The design presented is suitable for the f-to-2f carrier-envelope offset detection technique of stabilized optical frequency comb sources.

Two photon induced amplified spontaneous emission at low threshold from Styryl 7 dye incorporated DNA template

Studies on biophysical interactions between DNA-surfactant complexes and dye molecules are necessary to fully exploit its potential in optoelectronic devices. In this work investigations on nonlinear optical absorption and amplified spontaneous emission (ASE) of Styryl 7 dye (LDS 750) incorporating DNA-CTMA (deoxyribonucleic acid blended with cationic surfactant molecule, cetyltrimethyl-ammonium chloride) and PMMA (Poly methyl methacrylate) is reported. The nonlinear optical studies on the sample carried out using Z scan technique exhibits reverse saturable absorption with DNA -CTMA complex but with PMMA the sample behaves as a saturable absorber. We observed ASE at low pump energy for Styryl 7–DNA-CTMA film, when excited with a pulsed nanosecond Nd: YAG laser (λ = 532 nm) whereas ASE was not observed from dye incorporated with PMMA even with high pump energy. ASE characteristics were studied as a function of excitation energy density for the evaluation of threshold energy and exponential gain coefficient. The enhanced fluorescence and low threshold for ASE make Styryl 7 dye –DNA template a promising candidate for novel optoelectronic applications.

Stimulated Emission-Controlled Photonic Transistor on a Single Organic Triblock Nanowire.

In this work, we demonstrate a stimulated emission-controlled photonic transistor on a single organic triblock nanowire composed of alternate energy donor and acceptor. The population of acceptor excitons was engineered by energy transfer to achieve enhanced fluorescence, which was further amplified by the stimulated emission of the donor and the optical feedback in the nanowire microcavities, yielding a remarkable nonlinear amplification of the acceptor emission. On this basis, a prototype of photonic transistor with high nonlinear gain at very low pump energy was achieved. The results will provide a useful enlightenment for the rational design of novel all-optical switches with desired performances.

Optimization of deterministic controls for a cooling radiant wall coupled to a PV array

Thermally activated building systems (TABS) can work as thermal energy storage (TES) systems, which are useful in shifting the energy use of space cooling and heating in buildings. The present study analyses and optimizes simple deterministic control concepts for radiant wall supplied by a heat pump for cooling purposes. First, the “solar” concept was studied, which was focused on exploiting the output of a photovoltaic (PV) array. Secondly, a “peak load shifting” concept exploiting the low electricity cost and high heat pump energy efficiency during night periods was evaluated. The results showed that the “solar” concept saved between 57% and 95% in comparison to a conventional control in different PV installed capacities. Moreover, the optimized “peak load shifting” concept had lower operation cost than the conventional control with most of the PV configurations proposed. Therefore, the study showed that the investment in the PV array was fully harnessed only with specific controls. Furthermore, the “solar” control concepts were found to help achieving the goals of net-zero energy buildings by maximising self-consumption of renewable energies in the building, as well as reducing the total imported/exported energy.

Highly Nondegenerate Two-Photon Absorption in Silicon Wire Waveguides

Non-degenerate two-photon absorption (TPA) is investigated in a nanophotonic silicon waveguide in a configuration such that the dispersion of the nonlinear absorption and refraction cannot be neglected. It is shown that a signal wave can strongly be absorbed by cross-TPA by interaction with a low energy pump pulse (1.2\,pJ), close to the half-bandgap and experiencing low nonlinear absorption. The experiments are very well reproduced by numerical simulations of two-coupled generalized nonlinear Schr\"{o}dinger equations (GNLSE), validating the usual approximation made to compute the cross nonlinear coefficients in indirect-gap semiconductors. We show that the nonlinear dynamics can be well described by a single GNLSE despite the wavelength separation between the pump and the signal waves. We also demonstrate that in silicon wire waveguides and contrary to optical fibers, the dispersion of the nonlinear absorption is much larger than the dispersion of the Kerr effect. This could have an impact in the design of all-optical functions based on cross-TPA, as well as on the study of supercontinuum and frequency comb generation in integrated semiconductor-on-insulator platforms.

Simulation of the transient thermally induced beam quality degradation in end-pumped slab Yb:YAG amplifiers of hundred-mJ-level

The transient thermal distribution and thermally induced beam quality (M 2) degradation in low repetition (10 Hz) and hundred-mJ-level end-pumped Yb:YAG slab amplifiers with different thicknesses are discussed. Using Fast Fourier Transformation, the output beam quality is evaluated for different pump conditions, including variable pump power, single- or double-end pumping, and different pump beam widths. Simulation results show that for a slab amplifier operating at low repetition rates and high pump energy levels, adequate thermal property and output beam quality can be achieved by simply increasing the slab thickness.

Effect of Dehydrated Trehalose Matrix on the Kinetics of Forward Electron Transfer Reactions in Photosystem I

Abstract The effect of dehydration on the kinetics of forward electron transfer (ET) has been studied in cyanobacterial photosystem I (PS I) complexes in a trehalose glassy matrix by time-resolved optical and EPR spectroscopies in the 100 fs to 1 ms time domain. The kinetics of the flash-induced absorption changes in the subnanosecond time domain due to primary and secondary charge separation steps were monitored by pump–probe laser spectroscopy with 20-fs low-energy pump pulses centered at 720 nm. The back-reaction kinetics of P700 were measured by high-field time-resolved EPR spectroscopy and the forward kinetics of A 1A • − / A 1 B • − → F X ${\rm{A}}_{{\rm{1A}}}^{ \bullet - }/{\rm{A}}_{1{\rm{B}}}^{ \bullet - } \to {{\rm{F}}_{\rm{X}}}$ by time-resolved optical spectroscopy at 480 nm. The kinetics of the primary ET reactions to form the primary P 700 • + A 0 • − ${\rm{P}}_{700}^{ \bullet + }{\rm{A}}_0^{ \bullet - }$ and the secondary P 700 • + A 1 • − ${\rm{P}}_{700}^{ \bullet + }{\rm{A}}_1^{ \bullet - }$ ion radical pairs were not affected by dehydration in the trehalose matrix, while the yield of the P 700 • + A 1 • − ${\rm{P}}_{700}^{ \bullet + }{\rm{A}}_1^{ \bullet - }$ was decreased by ~20%. Forward ET from the phylloquinone molecules in the A 1 A • − ${\rm{A}}_{1{\rm{A}}}^{ \bullet - }$ and A 1 B • − ${\rm{A}}_{1{\rm{B}}}^{ \bullet - }$ sites to the iron–sulfur cluster FX slowed from ~220 ns and ~20 ns in solution to ~13 μs and ~80 ns, respectively. However, as shown by EPR spectroscopy, the ~15 μs kinetic phase also contains a small contribution from the recombination between A 1 B • − ${\rm{A}}_{1{\rm{B}}}^{ \bullet - }$ and P 700 • + . ${\rm{P}}_{700}^{ \bullet + }.$ These data reveal that the initial ET reactions from P700 to secondary phylloquinone acceptors in the A- and B-branches of cofactors (A1A and A1B) remain unaffected whereas ET beyond A1A and A1B is slowed or prevented by constrained protein dynamics due to the dry trehalose glass matrix.

Experimental demonstration of a collinear triple pulse grazing-incidence pumping scheme for a transient collisional pumped x-ray laser

We present a nickel-like Molybdenum x-ray laser (XRL) based on the transient collisional excitation scheme. Extending the double grazing-incidence pumping scheme to a triple pulse scheme with a nanosecond pre-pulse and two consecutive 3 ps pulses the output power of the XRL can be ∼6 times increased compared to existing configurations, while using a relatively low total pump energy of 0.7 J. Additionally we show that this setup can be extended to a double stage, oscillator and amplifier stage, XRL.

A train of backward Raman soliton pulses in hollow-core photonic crystal fibres filled with hydrogen gas

By using a novel hollow-core photonic crystal fibres (HC-PCFs) filled with hydrogen gas, the like-solitary pulse train in backward stimulated Raman scattering (BSRS) is experimentally reported. The pulse dynamics go through two processes. At first, the seed pulse amplification is uniform at relatively low pump energy. Secondly, at high pump energy, the seed one becomes amplifying and resharpenening to a train of successive solitons with secant-hyperbolic shapes. The asymptotic solution for BSRS equations is also used to explain qualitatively for these interesting phenomena in a transient regime.

Pump laser-induced space-charge effects in HHG-driven time- and angle-resolved photoelectron spectroscopy

With the advent of ultrashort-pulsed extreme ultraviolet sources, such as free-electron lasers or high-harmonic-generation (HHG) sources, a new research field for photoelectron spectroscopy has opened up in terms of femtosecond time-resolved pump-probe experiments. The impact of the high peak brilliance of these novel sources on photoemission spectra, so-called vacuum space-charge effects caused by the Coulomb interaction among the photoemitted probe electrons, has been studied extensively. However, possible distortions of the energy and momentum distributions of the probe photoelectrons caused by the low photon energy pump pulse due to the nonlinear emission of electrons have not been studied in detail yet. Here, we systematically investigate these pump laser-induced space-charge effects in a HHG-based experiment for the test case of highly oriented pyrolytic graphite. Specifically, we determine how the key parameters of the pump pulse—the excitation density, wavelength, spot size, and emitted electron energy distribution—affect the measured time-dependent energy and momentum distributions of the probe photoelectrons. The results are well reproduced by a simple mean-field model, which could open a path for the correction of pump laser-induced space-charge effects and thus toward probing ultrafast electron dynamics in strongly excited materials.

Optical Features of Spherical Gold Nanoparticle-Doped Solid-State Dye Laser Medium

The development of a new laser medium based on gold nanoparticle/dye-doped polymethylmethacrylate (PMMA) has been investigated. In particular, gold nanoparticles with small (16 nm diameter) spherical shape strongly influenced the absorption and fluorescence emission spectra of [2-[2-[4-(dimethylamino)phenyl]ethenyl]-6-methyl-4H-pyran-4-ylidene]-propanedinitrile (DCM) laser dye. Fluorescence quenching and enhancement of DCM emission were observed for various concentrations of gold nanoparticles (GNPs). Fluorescence intensity enhancement was recorded for the sample containing 1.5 × 1010 par/mL GNPs and doped with 3 × 10−5 mol/L DCM. Thermal photodegradation was significantly decreased by using low pump energy for laser emission.

Red to UV and blue up-conversion in alumina sol containing only Tm3+ or both Tm3+ and Yb3+ ions via low energy pumping

This paper reports the up-conversion emission properties of alumina sol containing only Tm3+ or both Tm3+ and Yb3+ ions under 650 nm pumping using a low power xenon lamp source. Two UV emission bands which centered at 349 nm for the 1I6 → 3F4 transition of Tm3+ ion and at 367 nm for the 1D2 → 3H6 transition of Tm3+ ion and two blue emission bands which centered at 457 nm for the 1D2 → 3H4 transition of Tm3+ ion and at 485 nm for the 1G4 → 3H6 transition of Tm3+ ion have been observed. The up-conversion emission follows a two-photon absorption process for both blue bands, and the UV band centered at 367 nm but follows a cross-relaxation process for the UV band centered at 349 nm. The concentration quenching effect is relatively low in this material under 650 nm pumping. Due to the back energy transfer from Yb3+ to Tm3+ ions, the intensity of UV emission corresponding to the 1I6 → 3F4 transition of Tm3+ ion is stronger in alumina sol samples containing both Tm3+ and Yb3+ ions than in which containing only Tm3+ ions.

Ultrafast all-optical modulation using a photonic-crystal Fano structure with broken symmetry.

We experimentally demonstrate ultrafast all-optical modulation using an ultracompact InP photonic-crystal Fano structure. In contrast to symmetric configurations previously considered, the use of a structure with broken symmetry in combination with a well-engineered Fano resonance is shown to suppress patterning effects as well as lower the energy consumption. These properties enable the achievement of error-free 10 Gbit/s modulation with low pump energy using realistic pseudorandom binary sequence patterns. At 20 Gbit/s, the bit error ratio remains well below the limit for forward error correction.

Spectral behavior of amplified back-scattered Stokes pulse in two-cell phase conjugating mirror

In this paper, the spectral behavior of two-cell phase conjugating mirror (PCM) with a two-pass Nd:YAG amplifier has been analyzed experimentally and theoretically. For this purpose, input intensity with single and multi-longitudinal modes has been investigated. The numerical model is based on focused geometry model (1+1 dimension) equations of Stokes back-scattered intensity and acoustic waves, for two-cell generator-amplifier phase conjugating mirror with proper boundary conditions that are solved simultaneously with the rate equations of Nd:YAG optical amplifier. Results of the Fourier analysis of the amplified intensity show considerable differences between Fourier amplitudes of the amplifier equipped with PCM and a two-pass amplifier with a conventional mirror under the same output energy. The amplifier with PCM has a completely filtered and different spectral behavior with clearly reduction of the beating between Fourier components of input optical field. Calculations show that the filtering of Fourier components by a PCM is done more effectively with lower pumping energy.

: ZnSe laser pumped by a nonchain electric-discharge HF laser at room temperature

The characteristics of a : ZnSe laser in a scheme with transverse pumping by a nonchain electric-discharge HF laser at room temperature are studied. Doping of ZnSe crystals with ions was performed by diffusion simultaneously through two surfaces under the conditions of thermodynamic equilibrium. It is found that the : ZnSe laser pulses are modulated by short spikes ( at half maximum at low pump energies), whose number decreases and modulation depth increases as the pump energy decreases to a threshold value. A laser pulse energy of is achieved at a pulse duration at half maximum of (at high pump energies); the possibility of a further increase in the energy of : ZnSe lasers pumped by nonchain HF lasers is discussed.

Two indigenous high sheared membrane modules' performance expatiation for the ultrafiltration of polyethylene glycol

Performance of the ultrafiltration (UF) with anti-thixotropic polyethylene glycol (PEG) 6000 was investigated in the present study using two forward-looking high sheared membrane modules called radial flow membrane module (RFMM) and turbine flow membrane module (TFMM). In addition, the present study has been extended to investigate the effect of both polyether sulfone (PES) and poly sulfone (PSf) membranes equipped within the individual module during ultrafiltration of hydrophilic PEG 6000. Moreover, applicability of the membrane-module combination was judged along with the membrane reusability and the power consumed by these modules. TFMM equipped with PSf membrane was found to be more effective in this respect at 20 kg m−3 initial PEG 6000 concentration and 0.2 MPa in creating maximum shear rate over the membrane attributing to moderate flux with low pump energy consumption. Around 97% water flux regains after two consecutive experiments with maximum initial PEG 6000 concentration in order to conclude the reusability of the post-washed membrane even the membrane was exposed to the highest level of concentration.

Low Threshold Lasing of GaN-Based VCSELs With Sub-Nanometer Roughness Polishing

Low threshold lasing at room temperature was achieved in optically pumped GaN-based vertical-cavity surface-emitting lasers (VCSELs) with sub-nanometer roughness polishing. The cavity region sandwiched by two dielectric distributed Bragg reflectors, incorporating InGaN/GaN multiquantum wells, a p-type AlGaN layer, and n- and p-type GaN layers, is a typical structure for electrically driven VCSELs. We observed lasing at a wavelength of 431.0 nm with a low threshold pumping energy density of ~ 3.2 mJ/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a high spontaneous emission coupling factor of ~ 0.09. These results were attributed to the significant reduction of the internal cavity loss by the removal of the high-dislocation GaN region, the reduction of cavity length, and the achievement of sub-nanometer level surface roughness (root mean square roughness of 0.3 nm) via inductively coupled plasma etching and chemical mechanical polishing. The loss mechanism is discussed and loss is quantitatively calculated in this letter.

Red, Green, and Blue Light‐Emitting Polyfluorenes Containing a Dibenzothiophene‐S,S‐Dioxide Unit and Efficient High‐Color‐Rendering‐Index White‐Light‐Emitting Diodes Made Therefrom

AbstractA series of blue (B), green (G) and red (R) light‐emitting, 9,9‐bis(4‐(2‐ethyl‐hexyloxy)phenyl)fluorene (PPF) based polymers containing a dibenzothiophene‐S,S‐dioxide (SO) unit (PPF‐SO polymer), with an additional benzothiadiazole (BT) unit (PPF‐SO‐BT polymer) or a 4,7‐di(4‐hexylthien‐2‐yl)‐benzothiadiazole (DHTBT) unit (PPF‐SO‐DHTBT polymer) are synthesized. These polymers exhibit high fluorescence yields and good thermal stability. Light‐emitting diodes (LEDs) using PPF‐SO25, PPF‐SO15‐BT1, and PPF‐SO15‐DHTBT1 as emission polymers have maximum efficiencies LEmax = 7.0, 17.6 and 6.1 cd A−1 with CIE coordinates (0.15, 0.17), (0.37, 0.56) and (0.62, 0.36), respectively. 1D distributed feedback lasers using PPF‐SO30 as the gain medium are demonstrated, with a wavelength tuning range 467 to 487 nm and low pump energy thresholds (≥18 nJ). Blending different ratios of B (PPF‐SO), G (PPF‐SO‐BT) and R (PPF‐SO‐DHTBT) polymers allows highly efficient white polymer light‐emitting diodes (WPLEDs) to be realized. The optimized devices have an attractive color temperature close to 4700 K and an excellent color rendering index (CRI) ≥90. They are relatively stable, with the emission color remaining almost unchanged when the current densities increase from 20 to 260 mA cm−2. The use of these polymers enables WPLEDs with a superior trade‐off between device efficiency, CRI, and color stability.

GaN-based high contrast grating surface-emitting lasers

GaN-based high contrast grating surface-emitting lasers (HCG SELs) with AlN/GaN distributed Bragg reflectors were reported. The device exhibited a low threshold pumping energy density of about 0.56 mJ/cm2 and the lasing wavelength was at 393.6 nm with a high degree of polarization of 73% at room temperature. The specific lasing mode and polarization characterisitcs agreed well with the theoretical modeling. The low threshold characteristics of our GaN-based HCG SELs faciliated by the Fano resonance can serve as the best candidate in blue surface emitting laser sources.

Red, green and blue lasing enabled by single-exciton gain in colloidal quantum dot films

Colloidal quantum dots exhibit efficient photoluminescence with widely tunable bandgaps as a result of quantum confinement effects. Such quantum dots are emerging as an appealing complement to epitaxial semiconductor laser materials, which are ubiquitous and technologically mature, but unable to cover the full visible spectrum (red, green and blue; RGB). However, the requirement for high colloidal-quantum-dot packing density, and losses due to non-radiative multiexcitonic Auger recombination, have hindered the development of lasers based on colloidal quantum dots. Here, we engineer CdSe/ZnCdS core/shell colloidal quantum dots with aromatic ligands, which form densely packed films exhibiting optical gain across the visible spectrum with less than one exciton per colloidal quantum dot on average. This single-exciton gain allows the films to reach the threshold of amplified spontaneous emission at very low optical pump energy densities of 90µJcm(-2), more than one order of magnitude better than previously reported values. We leverage the low-threshold gain of these nanocomposite films to produce the first colloidal-quantum-dot vertical-cavity surface-emitting lasers (CQD-VCSEL). Our results represent a significant step towards full-colour single-material lasers.