Laser Pump Power Research Articles

Heat transfer and thermoregulation within single cells revealed by transient plasmonic imaging

Summary Cells, as the basic unit of life, undergo continuous heat transfer and dissipation during their metabolism, which is related not only to fundamental cellular functions but also massive applications. Unfortunately, thus far, we still know little about the heat transfer properties at the cellular or subcellular levels. Here, we demonstrated a transient microscopic method to measure the heat transfer in single cells. The thermal conductivity of different regions within a single cell shows a wide heterogeneity, and heat transfer in the region near the cell membrane is more active than the central region. However, the median values of thermal conductivity between different individual cells are quite close. A cellular-level heat regulation that responds to environmental temperature is observed in warm-blooded humans and chickens rather than in cold-blooded bullfrogs. According to the temperature-dependent cell metabolism, we proposed a hypothesis for cellular control of heat dissipation, which might be the cellular-level foundation of body thermoregulation.

YAG:Yb crystal with non-linear doping ions distribution as promising active element for high average power laser systems

The influence of optical centers concentration profiles on thermal fields under high-power end-face diode pumping is analyzed using numerical model. It is shown that non-uniform distribution profiles of optical centers concentration are very promising for high average pump power laser amplifiers. The possibility of creating concentration profiles of optical centers in gradient-activated crystals with YAG matrix with a specified distribution along the growth axis of the crystal is demonstrated. A technology of growing gradient-activated single crystal involving active mirror as active element is proposed and discussed.

Features of repetitively-pulsed oscillation of an erbium fiber laser with a saturable absorber Bi2Te3 covered by silicone at various temperatures

The oscillation of erbium doped fiber lasers (EDFL) in the Q-switch mode is investigated. Etched out fiber tapers coated with two types of saturable absorbers (SA) are tested as passive Q-switches. SA of the first type comprises two-component silicone with nano-flakes of a Bi2Te3 single crystal dissolved in it. A thin film of Bi2Te3 synthesized by the Metalorganic Chemical Vapor Deposition (MOCVD) method on the surface of the fiber taper and coated with the same silicone served as SA of the second type. Housed within a refrigerator the fabricated sample of fiber taper with SA was in series plug into the fiber ring of the laser. A maximum is observed in the temperature dependence of the EDFL pulse repetition rate with both types of Q-switches. A decrease in temperature to –4 °C (for the first type) and to 9.5 °C (for the second one) led to the oscillation wavelength change from 1560 to 1530 nm. Cooling of Q-switches of the first and second types was accompanied by a decrease in the duration of laser pulses by a factor of 2.5 and 3.5, respectively, at a pump power corresponded to the conversion of laser oscillation from CW to repetitively-pulsed mode. At a given laser pump power, a 20% and 40% increment in the pulse repetition rate is observed upon cooling of passive Q-switches based on Bi2Te3 nanopowder-in-polymer and Bi2Te3 thin-film, up to temperatures of –14.8 °C and 4.4 °C, respectively, as compared to that one at room temperature. A diminution in the temperature of a passive Q-switch made it possible to obtain pulsed laser oscillation in a circuit that did not support the pulsed mode at room temperature.

Generation of color tunable emissions from Ho3+/Tm3+/Yb3+ co-doped YTaO4 phosphors through NIR excitation under different conditions (variation of concentration, excitation pump power and the external temperature)

This work reports the color tunable emission from Ho3+/Tm3+/Yb3+ co-doped YTaO4 phosphors synthesized through high temperature solid state reaction method. Pure phase formation and the effect of concentrations of dopants on the phase have been confirmed by X-ray diffraction (XRD) measurements. Vibrational structure and the phonon frequencies have been monitored using Fourier transform infrared (FTIR) measurements. The color tunability from green to blue regions has been studied by varying the concentration of sensitizer (Yb3+ ion) via upconversion (UC) process on excitation with 980 nm diode laser qualitatively as well as quantitatively. The variation in UC emission intensity in different regions at different concentrations of Yb3+ ion is explained using energy level diagram of Ho3+, Tm3+ and Yb3+ ions. The color tunability has been also observed with pump power of excitation source. The locus of the color coordinates in CIE diagram of the YTaO4:Tm3+, Ho3+, Yb3+ show different curvatures with different pump powers at different Yb3+ concentrations. The laser induced optical heating is responsible for variation in the color on increasing pump power. The color coordinates has been also investigated by varying the external temperature. The color tunable behaviours of YTaO4:Tm3+, Ho3+, Yb3+ phosphor by varying the concentration of Yb3+ ion, pump power of diode laser and at different external temperatures in the same material makes it suitable for the applications in security and fluorescence imaging.

Phase-locking of octave-spanning optical frequency comb based on Kerr-lens mode-locked Yb:KYW laser to reference laser

We phase locked an octave-spanning optical frequency comb based on a laser-diode-pumped Kerr-lens mode-locked Yb:KYW laser to a reference laser. We controlled the cavity length of the mode-locked laser to phase lock the mode frequency of the comb to the reference laser. This was conducted using a fast piezoelectric-actuated mirror on a lead-filled mount, which was aimed at damping the mechanical resonances. We achieved a servo bandwidth of 200 kHz, a residual phase noise of 0.47 rad, and a power concentration to a carrier of 91%. To extend the locking duration of the carrier-envelope offset frequency, we compensated its slow drift using the position of the Yb:KYW crystal while the pump-laser power was controlled to achieve its phase locking. We continuously maintained the full phase locking of the comb for 3 h until the reference lasers were out of lock.

On-chip tunable microdisk laser fabricated on Er3+-doped lithium niobate on insulator.

We demonstrate a C-band wavelength-tunable microlaser with an Er3+-doped high quality (∼1.8×106) lithium niobate microdisk resonator. With a 976 nm continuous-wave pump laser, lasing action can be observed at a pump power threshold lower than 400 µW at room temperature. Furthermore, the microdisk laser wavelength can be tuned by varying the pump laser power, showing a tuning efficiency of ∼-17.03pm/mW at low pump power below 13 mW, and 10.58 pm/mW at high pump power above 13 mW.

Photocatalytic, thermometric and internal heating multifunctional properties of Er3+/Yb3+-codoped MoO3 upconverting microparticles

To solve the existing challenges of luminescent materials for multifunctional applications, we developed Er3+/Yb3+-codoped MoO3 upconvering microparticles as promising platforms towards thermometry, optical heater and photocatalysis. At 980 nm light excitation, bright upconverison (UC) emissions are generated and the emission intensities are dependent on the doping content. The optimal doping content is 3 mol% and the UC emission mechanism is contributed by a tow-photon absorption process. Through analyzing the temperature-dependent UC emission intensities of thermally coupled levels of Er3+ ions, the thermometric properties of the final products are studied. The maximum absolute and relative sensitivities of the designed microparticles are 0.0093 K-1 and 2.9% K−1, respectively, which are insensitive to the dopant content. Furthermore, the laser pump power triggered internal heating properties of the developed samples are also investigated, in which the temperature of the samples is elevated from 318.7 to 587.6 K when the laser pump power is adjusted from 59 to 359 mW. Additionally, the designed microparticles can degrade pollutant efficiently upon full spectrum light irradiation. Compared with the MoO3, these compounds doped with Er3+ and Yb3+ ions show superior photocatalytic activities, in which the h+, ▪ and ·OH species can contribute to the involved photocatalytic mechanism. This work initiates a new insight to search for rare-earth ions doped upconverting materials for versatile applications.

Improvement of sensing sensitivity based on green emissions from Er-doped (AlGa)2O3 films

The temperature-dependent photoluminescence behaviors in green region of Er-doped (AlGa)2O3 films with different Al contents have been studied in the temperature range of 77–400 K. A reduced thermal quenching in green region was observed with the increase of host bandgap, resulting in an enhancement of green emissions. Subsequently, the temperature sensing properties of films were studied by using the fluorescent intensity ratio (FIR) technique based on the thermally coupled levels of 2H11/2 and 4S3/2 in Er3+. The enhanced thermal sensing properties were found with the increase of Al content in films. The absolute sensitivity of 0.0056 K−1 at 400 K was obtained at the Al content of 0.77, which is twice that of Ga2O3:Er film. Finally, the effect of adding Al content on the thermal effect induced by the laser pump power was investigated, and the results suggest that the thermal effect in all samples induced by the pump power can be negligible in this work. This work provides a useful insight for developing optical temperature sensors with high luminescence efficiency and sensitivity.

InGaN Resonant-Cavity Light-Emitting Diodes with Porous and Dielectric Reflectors

InGaN based resonant-cavity light-emitting diode (RC-LED) structures with an embedded porous-GaN/n-GaN distributed Bragg reflector (DBR) and a top dielectric Ta2O5/SiO2 DBR were demonstrated. GaN:Si epitaxial layers with high Si-doping concentration (n+-GaN:Si) in the 20-period n+-GaN/n-GaN stacked structure were transformed into a porous-GaN/n-GaN DBR structure through the doping-selective electrochemical wet etching process. The central wavelength and reflectivity were measured to be 434.3 nm and 98.5% for the porous DBR and to be 421.3 nm and 98.1% for the dielectric DBR. The effective 1λ cavity length at 432nm in the InGaN resonant-cavity consisted of a 30 nm-thick Ta2O5 spacer and a 148 nm-thick InGaN active layer that was analyzed from the angle-resolved photoluminescence (PL) spectra. In the optical pumping PL spectra, non-linear emission intensity and linewidths reducing effect, from 6.5 nm to 0.7 nm, were observed by varying the laser pumping power. Directional emission pattern and narrow linewidth were observed in the InGaN active layer with bottom porous DBR, top dielectric DBR, and the optimum spacer layer to match the short cavity structure.

Upconversion Luminescence, Laser Heating Effect and Temperature Sensing Properties of β-BiNbO4:Er3+/Yb3+

Upconversion (UC) phosphors of β-BiNbO4:Er3+/Yb3+ as temperature sensing materials were synthesized using the solid-state method. The structure was characterized by x-ray diffraction (XRD), revealing that all samples exhibited a single triclinic phase. Upon 980 nm laser excitation, the phosphors exhibited strong green emission and relatively weak red emission. Its possible luminescence mechanism is discussed based on the dependence of the UC emission spectra on the pump laser power. Finally, its temperature sensing properties were investigated using the temperature-dependent fluorescence intensity ratio (FIR) of two green emission bands originating from Er3+ ions. The thermal effect from laser irradiation and its influence on temperature sensing were also studied. Its absolute sensitivity SA exhibited a smaller change above 300 K, and reached a maximum value of 5.5‰ K−1 around 400 K. These results indicate that this type of qualified UC phosphor shows potential application in optical temperature sensors, especially at high temperature.

Strong second-harmonic generation in dielectric optical nanoantennas resulting from the hybridization of magnetic dipoles and lattice resonances

Magnetic dipole resonances supported by high refractive index dielectric nanoparticles have appeared recently as a new alternative to plasmonic nanostructures to manipulate light–matter interactions. The volume field enhancement within the particles significantly boosts some nonlinear processes, mitigating the need for conventional phase-matching conditions. In this paper, we show that by using an AlGaAs nanocylinder array whose lattice resonance spectrally matches the magnetic resonance of individual particles, the two resonances will couple with each other, leading to their strong hybridization and helping achieve a stronger circulation of the electric fields within the particles. As a result of this mode hybridization, at a low pump laser power intensity of 0. 053 G W / c m 2 , the efficiency of second-harmonic generation can be further enhanced by more than 2 orders of magnitude compared to that from an individual nanocylinder.

Optical temperature sensor based on upconversion luminescence of Er3+ doped GdTaO4 phosphors

AbstractFor the development of optical temperature sensor, a series of GdTaO4 phosphors with various Er3+‐doping concentrations (0, 1, 5, 10, 25, 35, 50 mol%) were synthesized by a solid‐state reaction method. The monoclinic crystalline structure of the prepared samples was determined by X‐ray diffraction (XRD). Under excitations of 980 and 1550 nm lasers, the multi‐photon‐excited green and red upconversion (UC) luminescence emissions of Er3+ were studied, and the critical quenching concentration of Er3+‐doped GdTaO4 phosphor was derived to be 25 mol%. By changing the pump power of laser, it was found that the two‐photon and three‐photon population processes happened for the UC emissions of Er3+‐doped GdTaO4 phosphors excited by 980 and 1550 nm lasers, respectively. Furthermore, based on the change of thermo‐responsive green UC luminescence intensity corresponding to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions of Er3+ with temperature, the optical temperature sensing properties of Er3+‐doped GdTaO4 phosphor were investigated under excitations of 980 and 1550 nm lasers by using the fluorescence intensity ratio (FIR) technique. It was obtained that the maximum absolute sensitivity (SA) and relative sensitivity (SR) of Er3+‐doped GdTaO4 phosphors are as high as 0.0041 K−1 at 475 K and 0.0112 K−1 at 293 K, respectively. These significant results suggest that the Er3+‐doped GdTaO4 phosphors are a promising candidate for optical temperature sensor.

Influence of Al2O3 on the photoluminescence and optical gain performance of Nd3+ doped germanate and tellurite glasses

Abstract We investigated the influence of aluminum oxide, Al2O3, on the photoluminescence (PL) spectrum and optical gain (at 1064 m) of neodymium ion, Nd3+, doped tellurium and germanium oxide glasses with compositions TeO2 − ZnO and GeO2 − PbO, respectively. The PL properties of both materials were studied using a continuous-wave diode laser operating at 808 nm, in resonance with the Nd3+ transition 4I9/2 → 4F5/2. For samples containing Al2O3 it was observed PL intensity growth up to 30% in comparison with the samples without Al2O3. Luminescence decay (τm) from the 4F3/2 level was measured monitoring the 4F/32 → 4I11/2 transition. From calculations of the Judd–Ofelt parameters, the radiative lifetimes, the emission cross -section (σem) and the quantum efficiency of 4F3/2 → 4I11/2 transition were determined; the effective linewidth (Δλeff) was calculated to determine the gain bandwidth product (σem x Δeff), figure of merit (σem x τm) and saturation intensity (Is) parameters. Optical gain measurements were performed using a pump laser at 808 nm and a probe laser at 1064 nm. For the samples with Al2O3 the relative gain at 1064 nm reached ≈ 2.8 dB/cm (pump laser power: 400 mW) indicating an enhancement of about 65% for TeO2 − ZnO and 120% for GeO2 − PbO with respect to the samples without Al2O3. The optical gain enhancement is correlated to the PL intensity behavior and increases due to the presence of Al2O3 because the coordination environment of the Nd3+ changes and become more asymmetric leading to the growth of the emission cross-section. The present study shows that Nd3+ doped tellurium and germanium oxide glasses containing Al2O3 present particularly good prospects to be used as optical amplifiers at 1064 nm.

Enhancing the long-term stability of dissipative Kerr soliton microcomb.

A temporal dissipative Kerr soliton (DKS) frequency comb can be generated in an optical micro-cavity relying on the rigid balance between cavity decay (dispersion) and parametric gain (nonlinear phase modulation) induced by an intense pump laser. In practice, to maintain such delicate double balances experienced by the intracavity soliton pulses, it requires precise control of the pump laser frequency and power, as well as the micro-cavity parameters. However, to date there still lacks experimental demonstration that simultaneously stabilizes all these key parameters to enhance the long-term DKS stability. Here, we demonstrate continuous working of a on-chip DKS microcomb for a record-breaking 14 days without showing any sign of breakdown. Such improved microcomb stability is enabled mainly by robust pump power coupling to the micro-cavity utilizing packaged planar-lightwave-circuit mode converters, and faithful locking of the pump frequency detuning via an auxiliary laser heating method. In addition to superior stability, the demonstrated DKS microcomb system also achieves favorable compactness, with all the accessory modules being assembled into a standard 4U case. We hope that our demonstration could prompt the practical utilization of Kerr microcombs in real-world applications.

Quantum correlations under the effect of a thermal environment in a triangular optomechanical cavity

We quantify the stationary correlations between the optical mode and the relative mechanical mode of a ring cavity composed of a fixed mirror and two movable ones in a triangular design. Using a ring cavity configuration not only enhances the optomechanical coupling by the displacement of the two movable mirrors, but also the circulation of the optical power inside the cavity enhances the intensity of the pumping power, not as in the case of a linear cavity. The bipartite covariance matrix is used to evaluate the logarithmic negativity as a measure of entanglement, the Gaussian quantum discord as a measure of total quantum correlations, and the mutual information as a measure of the overall correlations. The behavior of these quantities with respect to the environment’s temperature as well as other parameters, such as the laser pumping power and mass of the movable mirrors, is discussed.

Compound-induced transparency in three-cavity coupled structure* *Project supported by the National Natural Science Foundation of China (Grant No. 61575014).

We propose a three-cavity coupled cavity optomechanical (COM) structure with tunable system parameters and theoretically investigate the probe-light transmission rate. Numerical calculation of the system’s spectra demonstrates distinctive compound-induced transparency (CIT) characteristics, including multiple transparency windows and sideband dips, which can be explained by a coupling between optomechanically-induced transparency (OMIT) and electromagnetically-induced transparency. The effects of optical loss (gain) in the cavity, number and topology of active cavity, tunneling ratio, and pump laser power on the CIT spectrum are evaluated and analyzed. Moreover, the optical group delay of CIT is highly controllable and fast–slow light inter-transition can be achieved. The proposed structure makes possible the advantageous tuning freedom and provides a potential platform for controlling light propagation and fast–slow light switching.

Methods of hot wire creation for fiber-optical thermal anemometer

Subject of Research. The paper presents the study of various methods of optical radiation coupling from the fiber core into its cladding with the aim of creating a fiber-optic anemometer hot wire. The effectiveness of the described methods is evaluated by analyzing the obtained dependencies. Method. The structures of two optical fibers were studied, one of which was used to transmit an information signal, and the other — to create a hot wire. A Bragg grating was formed in the core of the first fiber, and a radiation coupling region was created in the second fiber. These fiber sections were aligned with each other and fixed by a tin-lead alloy. The temperature was measured by monitoring the spectral characteristics of fiber Bragg gratings inscribed by the phase mask method. The areas of radiation coupling were formed either by changing the fiber geometry using custom modes of the arc fusion splicer, or by creating a SMF-MMF-SMF transition. Main Results. Structures are developed which can be used as a hot wire of a fiber-optic anemometer sensitive element. The dependencies of the Bragg resonance wavelength shift on the pump laser power are obtained; the Bragg wavelength shift varies in the range from 0.15 nm to 3 nm as a result of a hot wire creation. The resulting curves are constructed after three experiments for each type of structure, taking into account the standard deviation. They make it possible to judge the effectiveness of various methods of radiation coupling. Comparative analysis of the studied methods is presented. Practical Relevance. The study describes the capabilities of fiber-optic anemometry when creating point and distributed sensors. The results of this work can be used in the areas where the creation of quasi-distributed and point diffusers is necessary, as well as partial or complete coupling of radiation from a fiber core.

Breach and recurrence of dissipative soliton resonance during period-doubling evolution in a fiber laser

We report on the experimental observation of period-doubling bifurcation of dissipative-soliton-resonance (DSR) pulses in a fiber laser passively mode-locked by using the nonlinear optical loop mirror. Increasing the pump power of the fiber laser, we show that temporally a stable, uniform DSR pulse train could be transformed into a period-doubling state, exhibiting two sets of pulse parameters between the adjacent cavity roundtrip. It is found that DSR pulses in the period-doubling state could maintain the typical feature of DSR pulse: fixed pulse peak power and linear variation in pulse width with respect to the pump power change. The mechanism for achieving period-doubling of DSR pulses is discussed.

Measurement of laser-induced dynamic structures on the surface of materials in a real time scale

The processes induced by laser radiation in the region of its interaction with matter are characterized by a high development rate and exclude direct contact of measuring detectors in the interaction region. The opportunity of structural adjustment of the irradiated surface of the material requires recording the temporal characteristics of these dynamic processes, which essentially determine the structural surface phase transitions in a heterogeneous medium. Therefore, for their diagnostics the highly sensitive, non-contact and inertialess registration methods are required. We used promising in this aspect optical recording methods based on the two channel scheme, i.e. the pump-probe techniques: the power pump laser and additional/probe laser radiation (brightness amplifies) to measure the development of nonlinear dynamic processes on the solid surface under laser radiation. The approach in frame of work of the such unified intelligent laser technological system results in control in time of processes of both laser thermal hardening with corresponding characteristics and generation of the spatial structures of different types on the surface of metallic units. We demonstrated some results for the laser technological processing with powerful laser radiation of a metal surface.

Reverse microemulsion synthesis of mixed α and β phase NaYF4:Yb,Er nanoparticles: calcination induced phase formation, morphology, and upconversion emission

A novel “water-in-oil” type reverse microemulsion assisted synthesis detail on the formation of mixed cubic and hexagonal (α + β) phase NaYF4:Yb,Er nanoparticles and their upconversion emission properties are presented. The effect of surfactants, fluorine precursors on the crystallographic phase fraction, crystallite size of NaYF4:Yb,Er nanoparticles on red upconversion emission is discussed. The NaYF4:Yb,Er nanoparticles synthesized with CTAB, and oleic acid surfactants give larger crystallite size and moderate hexagonal/cubic phase fraction. It has resulted very intense upconversion red emission. The oleic-acid-free preparation of NaYF4:Yb,Er nanoparticles resulted highly-agglomerated nanoparticles and low crystallite size, which gives less-intense upconversion emission. The cubic and hexagonal phase fractions of NaYF4:Yb,Er depends on surfactants, microemulsion, molar concentrations of precursors, and post-calcination. All these factors influence the mondispersibility and upconversion red emission properties. The 980 nm laser pump power dependent upconversion emission studies have confirmed the typical two-photon behavior in α + β phase NaYF4:Yb,Er nanoparticles. Their decay life was also measured to correlate the upconversion red emission intensity. The effect of mixed α + β phase NaYF4:Yb,Er nanoparticles on the 1530 nm NIR emission is also presented.