Low Pump Energy Research Articles

Distributed feedback laser action in reflection geometry from a dye-doped polymer film

Rhodamine 6G doped poly(methyl methacrylate) thin films were prepared on glass substrates. Tuneable distributed feedback (DFB) lasing output in a reflection grating geometry was realized in the films. Pure gain coupling and an additional index coupling were created in the films by the two crossing pump beams. Under low pump energy, a permanent gain modulation caused by dye bleaching was generated. An index modulation of the medium caused by photodamage was induced at higher pump energy. Dual-peak DFB lasing emission indicative of the existence of the index grating was observed under these conditions.

High-brightness optical-field-ionization collisional-excitation extreme-ultraviolet lasing pumped by a 100-TW laser system in an optically preformed plasma waveguide

Recent study on optical-field-ionization collisional-excitation extreme-ultraviolet lasing of Ni-like krypton at 32.8 nm pumped by a 100-TW laser system with an optically preformed plasma waveguide is reported. By using a 9-mm-long pure krypton plasma waveguide fabricated with the axicon-ignitor-heater scheme, the 32.8-nm extreme-ultraviolet laser provided an average output of 1012 photons/pulse at pump energy of 1 J, more than one order of magnitude enhancement relative to the previous results with the same scheme at pump energy of 235 mJ. It is also found the far-field pattern of laser beams varies from a single peak profile at low pump energy to an annular profile at high pump energy due to over-ionization of krypton ions at the center of the plasma channel.

Flow Drag and Heat Transfer Reduction Characteristics of Organic Brine (Potassium Acetate) and Inorganic Brine (Calcium Chloride) Solutions with Nonionic Surfactant

Flow drag and heat transfer reduction effects are useful in heat energy transportation systems and can lead to lower pumping energy requirements. The purpose of this research is to describe the flow drag and heat transfer reduction characteristics of organic (potassium acetate) and inorganic (calcium chloride) brine solutions. The nonionic surfactant oleyl dihydroxyethyl amine oxide (ODEAO) is used as a drag-reducing additive. The pipe friction coefficient and heat transfer coefficient are investigated experimentally in a straight pipe for each type of solution with ODEAO. These coefficients are found to be lower than those of water in the turbulent flow range. However, the rod-like micelles of ODEAO, which are necessary to induce the flow drag reduction effect, are not readily formed in these solutions. Hence, the flow drag and heat transfer reduction effects are measured only under limited conditions and it is difficult to apply these solutions practically as heat transfer media.

Femtosecond primary charge separation in Synechocystis sp. PCC 6803 photosystem I

The ultrafast (< 100 fs) conversion of delocalized exciton into charge-separated state between the primary donor P700 (bleaching at 705 nm) and the primary acceptor A 0 (bleaching at 690 nm) in photosystem I (PS I) complexes from Synechocystis sp. PCC 6803 was observed. The data were obtained by application of pump–probe technique with 20-fs low-energy pump pulses centered at 720 nm. The earliest absorbance changes (close to zero delay) with a bleaching at 690 nm are similar to the product of the absorption spectrum of PS I complex and the laser pulse spectrum, which represents the efficiency spectrum of the light absorption by PS I upon femtosecond excitation centered at 720 nm. During the first ∼ 60 fs the energy transfer from the chlorophyll ( Chl) species bleaching at 690 nm to the Chl bleaching at 705 nm occurs, resulting in almost equal bleaching of the two forms with the formation of delocalized exciton between 690-nm and 705-nm Chls. Within the next ∼ 40 fs the formation of a new broad band centered at ∼ 660 nm (attributed to the appearance of Chl anion radical) is observed. This band decays with time constant simultaneously with an electron transfer to A 1 (phylloquinone). The subtraction of kinetic difference absorption spectra of the closed (state P700 +A 0A 1) PS I reaction center (RC) from that of the open (state P700A 0A 1) RC reveals the pure spectrum of the P700 +A 0 − ion–radical pair. The experimental data were analyzed using a simple kinetic scheme: An* → k 1 [(PA 0)*A 1 → < 100 fs P +A 0 −A 1] → k 2 P +A 0A 1 −, and a global fitting procedure based on the singular value decomposition analysis. The calculated kinetics of transitions between intermediate states and their spectra were similar to the kinetics recorded at 694 and 705 nm and the experimental spectra obtained by subtraction of the spectra of closed RCs from the spectra of open RCs. As a result, we found that the main events in RCs of PS I under our experimental conditions include very fast (< 100 fs) charge separation with the formation of the P700 +A 0 −A 1 state in approximately one half of the RCs, the ∼ 5-ps energy transfer from antenna Chl* to P700A 0A 1 in the remaining RCs, and ∼ 25-ps formation of the secondary radical pair P700 +A 0A 1 −.

Upconversion nanoparticles in biological labeling, imaging, and therapy

Upconversion refers to non-linear optical processes that convert two or more low-energy pump photons to a higher-energy output photon. After being recognized in the mid-1960s, upconversion has attracted significant research interest for its applications in optical devices such as infrared quantum counter detectors and compact solid-state lasers. Over the past decade, upconversion has become more prominent in biological sciences as the preparation of high-quality lanthanide-doped nanoparticles has become increasingly routine. Owing to their small physical dimensions and biocompatibility, upconversion nanoparticles can be easily coupled to proteins or other biological macromolecular systems and used in a variety of assay formats ranging from bio-detection to cancer therapy. In addition, intense visible emission from these nanoparticles under near-infrared excitation, which is less harmful to biological samples and has greater sample penetration depths than conventional ultraviolet excitation, enhances their prospects as luminescent stains in bio-imaging. In this article, we review recent developments in optical biolabeling and bio-imaging involving upconversion nanoparticles, simultaneously bringing to the forefront the desirable characteristics, strengths and weaknesses of these luminescent nanomaterials.

Growth profile of stimulated Raman anti‐Stokes scattering influenced by fluorescence seeding in liquid‐core optical fiber

AbstractWe demonstrated the growth profile of stimulated Raman anti‐Stokes scattering (SRS) of carbon disulfide (CS2) influenced by fluorescence seeding of all‐trans‐β‐carotene and rhodamine‐B (RhB) in liquid‐core optical fiber (LCOF). The pump energy which was needed to build up the first‐order anti‐Stokes radiation of CS2 solutions with the fluorescence seeding was lower than that of CS2 solutions without fluorescence seeding because of the fluorescence enhancement effect on the intensity of the first‐order Stokes radiation. The first‐order anti‐Stokes radiation of the RhB solution (10−8 M) was built up at a lower pump energy than that of the all‐trans‐β‐carotene solution (10−6 M), and the intensity of the first‐order anti‐Stokes radiation of the RhB solution was higher than that of the all‐trans‐β‐carotene solution. Simultaneously, the coupled wave differential equations were obtained by the theoretical derivation, and the growth profile of the first‐order anti‐Stokes radiation was theoretically calculated with and without the fluorescence seeding by these equations. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Improved output energy characteristic of optical limiting based on double stimulated Brillouin scattering

In order to improve the optical limiting performance based on stimulated Brillouin scattering (SBS), a method based on double SBS is proposed in this paper. The dependence of the output energy of optical limiting based on double SBS on the pump energy is numerically simulated, and experimentally validated with an Nd:YAG seed-injected laser. The results indicate that only the first SBS optical limiting works in the case of low pump energy. However, as the pump energy increases, the second SBS process can be activated if the transmitted power of the first SBS is still above the SBS threshold. Therefore, the output energy characteristic of optical limiting based on double SBS is much better than that based on single SBS. Owing to the sub-nanosecond response time and a high power threshold, the SBS optical limiting can provide protection in high power laser systems.

Optical parametric generation of nearly transform-limited mid-infrared pulses in dispersion-engineered nonlinear waveguides

Optical parametric generation in dispersion-engineered waveguides fabricated by proton exchange in periodically poled lithium niobate is numerically investigated as a means for producing widely tunable mid-infrared ultrashort pulses starting from low energy pump pulses at a 1.55 microm wavelength and with 100 fs duration, which are typical parameters of amplified Er-fiber oscillators. Numerical evidence is given about the generation of sub-100 fs nearly transform-limited pulses in the 2.4-4.4 microm spectral range.

Multimode laser emission from dye doped polymer optical fiber

Multimode laser emission is observed in a polymer optical fiber doped with a mixture of Rhodamine 6G (Rh 6G) and Rhodamine B (Rh B) dyes. Tuning of laser emission is achieved by using the mixture of dyes due to the energy transfer occurring from donor molecule (Rh 6G) to acceptor molecule (Rh B). The dye doped poly(methyl methacrylate)-based polymer optical fiber is pumped axially at one end of the fiber using a 532 nm pulsed laser beam from a Nd:YAG laser and the fluorescence emission is collected from the other end. At low pump energy levels, fluorescence emission is observed. When the energy is increased beyond a threshold value, laser emission occurs with a multimode structure. The optical feedback for the gain medium is provided by the cylindrical surface of the optical fiber, which acts as a cavity. This fact is confirmed by the mode spacing dependence on the diameter of the fiber.

Study on stimulated Brillouin scattering pulse waveform

In this paper, the pulse waveform of stimulated Brillouin scattering (SBS) is investigated experimentally and theoretically. The variations of SBS pulse waveform with pump parameters, structural parameters and medium parameters are experimentally investigated with a Nd∶YAG Q-switched laser，and numerically simulated using SBS theory model. The theoretical calculations are in good agreement with the experimental results. The results indicate that modulation of pulse waveform is difficult to realige with low pump energy, short focal length, long lens-cell distance and long phonon life time. The influence of the pump parameters, structural parameters and medium parameters on SBS pulse waveform is discussed extensively.

The influence of absorption and fluorescence from the solution on the stimulated Raman threshold of CS2 in liquid-core optical fiber

It is shown from experiments that the stimulated Raman thresholds of the first and the second Stokes lines of CS2 are influenced by the absorption and fluorescence from the solution of β-Carotene in CS2 in liquid core optical fiber. The threshold of the first Stokes line of CS2 becomes higher when the concentration of the solution increases. And the second Stokes line of CS2 can be observed at a lower pump energy in the solution of β-Carotene in CS2 compared with that of the solution of pure CS2. Then the theoretic explanations are given and the theoretic results agree well with the experimental results.

High-gain degenerated optical parametric chirped-pulse amplification in periodically poled LiTaO3

The gain curve in periodically poled LiTaO3 crystal (PPLT) was calculated for type 0 (e+e→e) quasi-phase matching (QPM). A high-gain amplifier centered at 1064nm based on degenerated optical parametric chirped-pulse amplification was built. The gain of ～106 and ～10.3% conversion efficiency were achieved with low pump energy of several hundreds of μJ. The experimental results are consistent with the simulation.

All-optical silicon modulators based on carrier injection by two-photon absorption

This paper presents a theoretical analysis of a silicon all-optical modulator based on free-carrier injection by two-photon absorption (TPA) in a highly light-confining structure. In spite of the weak optoelectronic properties of silicon, strong light confinement allows high modulation depths in very compact devices requiring low-energy pump pulses. This analysis is applied to 1-5 mum radius silicon ring resonators with the pump pulse coupled on-chip and including in the model the scattering loss due to sidewall roughness originating from the fabrication process. The calculations show that using this scheme, modulation depths greater than 80% can be achieved, with no more than 3 pJ of pump pulse energy, at speeds on the order of 10 GHz

Study of the competition between forward and backward stimulated Raman scattering in methane

Simultaneous forward and backward stimulated Raman scattering (SRS) in methane pumped by a single longitudinal mode Nd:YAG laser at 355 nm has been investigated both experimentally and numerically. For forward SRS, a maximum energy-conversion efficiency of 55% was obtained under 24 atm, while for backward SRS the corresponding figure was 58% under 4.7 atm. Under low pressures or at low pump energies, the conversion efficiency for backward SRS was found to be much higher than that for forward SRS, while the situation is quite the contrary under high pressures and at high pump energies. A quasi-two-dimensional numerical model is introduced to elucidate the competition between forward and backward SRS; we conclude that the high-pressure and high-pump-energy experimental results should be caused by the thermal defocusing effect in the SRS process. This is confirmed by the experimental fact that a decrease of the pulse-repetition rate increases the conversion efficiency for backward SRS but decreases that for forward SRS under high pressures. Our calculated results are in good agreement with the experimental results at a pulse-repetition rate of 2 Hz.

Ultrafast all-optical modulation on a silicon chip

We experimentally demonstrate ultrafast all-optical modulation using a micrometer-sized silicon photonic integrated device. The device transmission is strongly modulated by photoexcited carriers generated by low-energy pump pulses. A p-i-n junction is integrated on the structure to permit control of the generated carrier lifetimes. When the junction is reverse biased, carriers are extracted from the device in a time as short as 50 ps, permitting greater than 5 Gbit/s modulation of optical signals on a silicon chip.

Transition from single-mode to multimode operation of an injection-seeded pulsed optical parametric oscillator

Optical-heterodyne measurements are made on ~842-nm signal output of an injection-seeded optical parametric oscillator (OPO) based on periodically poled KTiOPO4 pumped at 532 nm by long (~27-ns) pulses from a Nd:YAG laser. At low pump energies (</= 2.5 times the free-running threshold), the narrowband tunable OPO output is single-longitudinal-mode (SLM) and frequency chirp can be <10 MHz, much less than the transform-limited optical bandwidth (~17.5 MHz). We explore the transition from SLM operation to multimode operation as pump energy or phase mismatch are increased, causing unseeded cavity modes to build up later in the pulse.

Third harmonic beam profile generated in atmospheric air using femtosecond laser pulses

We present, both experimentally and theoretically, the results on third harmonic generation in air during the filamentation of a powerful femtosecond laser pulse. The third harmonic beam pattern shows a central spot on the propagation axis at lower pump energy and is then surrounded by bright third harmonic conical emission at higher pump energy. We argue that the combined action of self-focusing and plasma generation in air plays an important role for the on-axis and off-axis phase-matching conditions along the filament resulting in high conversion efficiency. The experimental results are in good qualitative agreement with numerical simulations.

Generation of high repetition rate femtosecond Ti:sapphire regenerative amplified pulse of high beam quality for ultra-precision machining

On the basis of calculation and analysis on femtosecond amplification gain saturation and femtosecond pulse stretching, we believe it is possible to achieve moderate energy femtosecond regenerative amplification without stretcher if the amplifying cavity parameters is optimized and the pumping pulse energy is changed. According to the conclusion, applying low pumping energy and Ti:sapphire off-focusing technique to the amplifier, we do the experiment about high repetition rate femtosecond Ti:sapphire regenerative amplification and compressing without the stretcher. The femtosecond amplified pulse of perfect beam quality is obtained. The energy of amplified pulse is more than 100μJ.The amplified pulse repetition is 1kHz. The spectrum FWHM is 7.7nm.After the compressing,the pulsewidth is 500fs.

Low pumping energy mode of the “optical bars”/“optical lever” topologies of gravitational-wave antennae

The “optical bars”/“optical lever” topologies of gravitational-wave antennae allow to obtain sensitivity better that the Standard Quantum Limit while keeping the optical pumping energy in the antenna relatively low. Element of the crucial importance in these schemes is the local meter which monitors the local test mirror position. Using cross-correlation of this meter back-action noise and its measurement noise it is possible to further decrease the optical pumping energy. In this case the pumping energy minimal value will be limited by the internal losses in the antenna only. Estimates show that for values of parameters available for contemporary and planned gravitational-wave antennae, sensitivity about one order of magnitude better than the Standard Quantum Limit can be obtained using the pumping energy about one order of magnitude smaller energy than is required in the traditional topology in order to obtain the Standard Quantum Limit level of sensitivity.

Long lifetime and high repetition rate operation from distributed feedback plastic waveguided dye lasers

Abstract Long lifetime and high repetition rate laser operation was demonstrated from laser-dye-doped waveguides with distributed feedback (DFB) structures. The waveguides were fabricated with a spin-coating and lithography techniques, and DFB structure was written by an ultraviolet holography technique. A compact frequency-doubled Nd:YAG microchip laser was used as a pumping source, and the laser output wavelength range of 575–945 nm was obtained from 10 different kinds of laser-dye-doped plastic film and the laser performance was evaluated about 5 of them. Very low pumping energy requirement of around several μJ could extend the durabilities of the DFB dye-doped waveguides, and the lifetime of more than one million shots was obtained. Further a high repetition laser operation up to 1000 pps was demonstrated with an output energy stability of less than ±0.5%. A palm-top size tunable laser is realized by this configuration.