Laser Pump Power Research Articles

Influence of low temperature on white light emission from graphene-based microchip

The laser-induced white emission of the graphene-based microchip was investigated under near-infrared region laser irradiation. The emission was characterized by an excitation threshold and an exponential dependence on the pump laser power. A decrease in temperature caused an increase in both the number of absorbed photons and the emission threshold. This dependence can be explained by the multiphoton ionization process in (sp2, sp3) hybridized domains.

Spectral Investigation of Yb3+/Ho3+/Tm3+:Y2Si2O7 Upconverting Nanophosphors for the Usage of Temperature Sensing

Rare earth (Yb3+, Ho3+, Tm3+) yttrium disilicate phosphors were produced by sol-gel technique and heated at 1050 °C temperature. The sizes of the phosphors vary between 20-30 nm according to the images obtained from the Transmission Electron Microscope. The up-conversion (UC) emissions of the nanopowders were measured in the range of 500–900 nm wavelength under 950 nm laser excitation. A linear increase with power was observed in the emission intensity ratio depending on the laser excitation power. Using the FIR technique, the phosphor’s temperature was determined by the heating effect caused by the laser pump power. Due to the change in intensity ratio versus temperature, the temperature sensitivity at 428 K was calculated as 0.781x10-2K-1 and it was suggested that it can be used as a promising temperature sensor probe in photonic devices.

X-ray scattering exhibits time-resolved view of rhodopsin activation.

Visual rhodopsin is an excellent model system to understand the spatio-temporal dynamics of class-A G-protein-coupled receptors (GPCRs). We aim to understand the mechanistic details of how the changes in retinal cofactor propagate to become protein-wide conformational changes over large orders of time. Our hypothesis was that a volumetric expansion occurs in the light-activation process [1]. Here we show the first time-resolved X-ray scattering-based detection of the expansion of rhodopsin leading to the signaling state. We conducted time-resolved small-angle and wide-angle scattering (TR-SAXS and TR-WAXS, respectively) of rhodopsin solubilized in CHAPS detergent at the BioCARS synchrotron beamline (Advanced Photon Source). The photochemistry was initiated with a green (527-nm) laser and probed with X-rays at time delays between 10 ns to 128 ms to collect small and wide-angle difference scattering profiles. Our controls were the retinal-free apoprotein opsin pumped with either green (527-nm) or red (650-nm) light, and the rhodopsin holoprotein pumped with off-resonance red light (650 nm). Optical (pump) laser power titrations were conducted to understand the how visible light modulates the conformational changes following the activation. The absence of difference scattering signals in both controls confirmed the capture of structural information from excitation of the retinal chromophore. Our analysis shows time-dependent increases in the radius of gyration and the volume of the light-activated state versus the inactive dark state which are important for effector proteins to function in visual signaling. The solvent heating found in the high-q region (2-2.5Å−1) (TR-WAXS) was used to quantify time-resolved temperature changes in the protein. The analysis showed that multiple photons are absorbed by rhodopsin, which we attribute to sequential absorption by intermediates in the photocycle as the protein traverses its conformational landscape. [1] S.M.D.C. Perera et al. (2018) J.Phys.Chem.Lett. 9, 7064−7071.

Ultrafast L Band Soliton Pulse Generation in Erbium-Doped Fiber Laser Based on Graphene Oxide Saturable Absorber

We demonstrate a simple mode-locked Erbium-doped fiber laser (EDFL) based on self-synthesized saturable absorber (SA) by combining graphene oxide (GO) and polyethylene oxide (PEO) solutions to form a GO-PEO thin film. This thin film was incorporated into an Erbium-doped fiber laser (EDFL) with a cavity length of 9 m. Our EDFL could operate at a 22 MHz repetition rate with a 0.8 ps pulse duration. The laser also showed stable soliton pulses under various laser pump power values. Our reported results show that GO-PEO SA is effective and proven as a cost-effective material for saturable absorbers for EDFLs.

Расчетно-экспериментальная оценка реакции волоконного лазера на импульсное воздействие тормозного излучения

Experiments have been carried out to study the transient radiation-induced absorption in the active core of a double-clad ytterbium fiber and the response of a laser based on it under the impact of pulsed X-rays. It has been found that the time of loss of laser performance (downtime) under pulsed irradiation increases with an increase in the absorbed dose rate of radiation and a decrease in the laser pump power and reaches values of ~1 ms. An analysis of the experimental results shows that the laser response to the action of X-rays pulse is determined by radiation-induced losses in the active fiber core. A experimental-calculated method for estimating the radiation reaction of a laser, based on the results of studies of the active fiber, is proposed.

Kerr Frequency Comb and Stimulated Raman Comb Covering S+C+L+U Band Based on a Packaged Silica Spherical Microcavity

Optical microresonators supported whispering gallery modes (WGMs) are one of the most cost-effective platforms for optical frequency comb generated due to their advantages of ultra-high quality ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) factor and ultra-low mode volume. In this paper, we report a portable and robust packaged silica spherical microcavity by melting the end of a standard single-mode fiber with ultra-high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${10}^8$</tex-math></inline-formula> , and theoretically and experimentally demonstrate a broadband optical frequency comb (OFC) generation including Kerr OFC and stimulated Raman comb. Kerr OFCs are separated by one, two, eight and twelve free spectral ranges corresponding to 1.4, 2.8, 11.2, and 16.8 nm, respectively. The transition between Kerr OFC and stimulated Raman comb is achieved by changing the pump laser power and the detuning frequency resulting from gain competition between modulation instability and Raman gain. Benefitting from the dispersion control and ultra-high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor persistence in our packaged microcavity, OFC can be adjusted continuously covering from S-band to C-band, L-band and U-band. We also explain these results by numerical simulations using a model framework combined with the Lugiato-Lefever equation and Raman response function.

Accurate Determination of Spin-Exchange Relaxation in a Self-Compensated Atomic Comagnetometer

The spin-exchange (SE) relaxation of the electron spins limits the sensitivity of the self-compensated atomic co-magnetometer. In this paper, a novel method for measuring the SE relaxation based on the pulse response of the comagnetometer is proposed. The SE relaxation is measured from the difference between the transverse and longitudinal relaxation of the electron spins, which are synchronously extracted from the responses along the probe and pump laser directions to a series of pulsed magnetic fields. Furthermore, we investigate the variation of the SE relaxation with different pump laser power densities and cell temperatures based on this method. The results indicate that there is a maximum of the SE relaxation with the increase of the pump laser power density, and the pump laser power density corresponding to the maximum increases with the cell temperature. The theory and method presented here not only shed light on the way to suppress the SE relaxation in the self-compensated comagnetometer, but also have the potential to be applied to other optically pumped atomic sensors.

Optical Supercontinuum Generation via Rotational and Vibrational Molecular Cavity Optomechanics

AbstractThe solid high quality (Q) factor whispering gallery mode microcavities are demonstrated as an excellent experimental platform for enhanced light–matter interactions, and are applied in the studies of nonlinear optics, quantum optics, and sensing. However, the interaction between the microcavity and liquid anisotropic molecule, which is unique for abundant vibrational and rotational degrees of freedom, is rarely studied. Here, the gap is bridged by filling an optofluidic microbubble resonator with carbon disulfide, and the related anisotropic molecular cavity optomechanics effects are investigated. Due to the enhanced coupling between the optical mode and the rotation/vibration of molecules, stimulated Rayleigh–Kerr/Raman–Kerr scattering effects are observed. Molecular cavity optomechanics provides a broadband gain for generating Stokes photons in high‐Q optical modes, and eventually allows quasi‐supercontinuum generation with a bandwidth of 436 nm under a low continuous laser pump power of about 10 mW. This work opens a new avenue for strong light–matter interactions by exploring rotational and vibrational molecular cavity optomechanics, which provides a promising platform for nonlinear optics, cavity‐enhanced molecular reorientation dynamics, and novel optical sources.

Analysis on the effect of electron spin polarization on a hybrid optically pumped K-Rb-21Ne co-magnetometer.

In this paper, the effect of longitudinal electron spin polarization under the combined action of alkali metal density ratio and pump laser power density on the hybrid optically pumped co-magnetometer operated in the spin-exchange relaxation-free (SERF) regime is studied. The AC response model of rotation velocity and magnetic noise of the SERF co-magnetometer system is proposed, and the factors of frequency and system bandwidth are considered. Based on the proposed response model, the error equation of the system is obtained, and the relationship between alkali metal density ratio and pump laser power density and the system noise response is theoretically analyzed and experimentally tested. The results show that when the product of pumping rate and alkali metal density ratio is greater than the electron spin relaxation rate, there is a longitudinal electron spin polarization point that minimizes the system error. In addition, the range of minimum error calculated results obtained by changing the pumping rate for the cells with different alkali metal density ratios is within 5% of the average value, that is, their minimum error potential is roughly the same within a certain range. Under the experimental conditions in this paper, due to the limitation of the electron spin relaxation rate and the operating capacity of the pump laser, the optimal alkali metal density ratio range is about 1/100-1/300.

Upconverting nanoparticles as primary thermometers and power sensors

Luminescence thermometry is a spectroscopic technique for remote temperature detection based on the thermal dependence of the luminescence of phosphors, presenting numerous applications ranging from biosciences to engineering. In this work, we use the Er3+ emission of the NaGdF4/NaGdF4:Yb3+,Er3+/NaGdF4 upconverting nanoparticles upon 980 nm laser excitation to determine simultaneously the absolute temperature and the excitation power density. The Er3+2H11/2→4I15/2 and 4S3/2→4I15/2 emission bands, which are commonly used for thermometric purposes, overlap with the 2H9/2 →4I13/2 emission band, which can lead to erroneous temperature readout. Applying the concept of luminescent primary thermometry to resolve the overlapping Er3+ transitions, a dual nanosensor synchronously measuring the temperature and the delivered laser pump power is successfully realized holding promising applications in laser-supported thermal therapies.

Spatial Properties of Entangled Two-Photon Absorption

We experimentally study entangled two-photon absorption in rhodamine 6G as a function of the spatial properties of a high flux of broadband entangled photon pairs. We first demonstrate a key signature dependence of the entangled two-photon absorption rate on the type of entangled pair flux attenuation: linear, when the laser pump power is attenuated, and quadratic, when the pair flux itself experiences linear loss. We then perform a fluorescence-based Z-scan measurement to study the influence of beam waist size on the entangled two-photon absorption process and compare this to classical single- and two-photon absorption processes. We demonstrate that the entangled two-photon absorption shares a beam waist dependence similar to that of classical two-photon absorption. This result presents an additional argument for the wide range of contrasting values of quoted entangled two-photon absorption cross sections of dyes in literature.

All-Optical Method of Determining Laser Power from the Photomechanical Effect

A method to determine the power of a continuous wave laser from photothermal heating of a poly(dimethyl siloxane) film is reported. The base was doped with oil red O and cured on a surface relief grating. The grating period was shown to increase proportional to the temperature by monitoring the decrease in diffraction angle of a probe beam. A 10s illumination period of a continuous wave (CW) pump beam absorbed by the film increased the film’s temperature, which resulted in a local strain that could be modeled using the two-dimensional heat kernel. The amplitude of the transient response was found to be linearly correlated with the pump laser power.

Laser diode-pumped compact hybrid lithium niobate microring laser.

We demonstrate a compact hybrid lithium niobate microring laser by butt coupling a commercial 980-nm pump laser diode chip with a high-quality Er3+-doped lithium niobate microring chip. Single-mode lasing emission at 1531-nm wavelength from the Er3+-doped lithium niobate microring can be observed with the integrated 980-nm laser pumping. The compact hybrid lithium niobate microring laser occupies the chip size of 3 mm × 4 mm × 0.5 mm. The threshold pumping laser power is 6 mW and the threshold current is 0.5 A (operating voltage 1.64 V) at atmospheric temperature. The spectrum featuring single-mode lasing with small linewidth of 0.05 nm is observed. This work explores a robust hybrid lithium niobate microring laser source which has potential applications in coherent optical communication and precision metrology.

White emission of stable Yb3+/Er3+/Tm3+-tridoped Y2O3–ZnO ceramic phosphor tuned by altering Tm3+ concentration and excitation laser pump power

In this study, a series of well-crystallized Yb3+/Er3+/Tm3+-tridoped Y2O3–ZnO ceramic phosphors were prepared using sol–gel synthesis, and the phosphor structures were studied using X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The phosphors had excellent physical stability and porous structure. All phosphors generated blue, green, and red emission bands attributed to Tm: 1G4→3H6, Er: 2H11/2 (4S3/2)→4I15/2, and Er: 4F9/2 → 4I15/2 radiative transitions, respectively. The emissions were intensified twice by tuning the Tm3+ ratio in the host matrix Y2O3 and ZnO parts. The color coordinates were adjusted by tuning both the Tm3+ concentration and the excitation laser pump power to shift the color coordinates and only enhance the brightness, respectively. Meanwhile, heating phosphors can also linearly adjust the color coordinates of the luminescence. Therefore, it can also be used as a fluorescence thermometer in the field of temperature sensor. The study findings will broaden the phosphor practical application potential.

Multifunctional rare earth ions-doped Ba2LaF7 nanocrystals for simultaneous temperature sensing and photothermal therapy

As an urgent problem, cancer has boosted the development and application of many treatment technologies in biomedicine. Photothermal therapy with precise control for tumors has gained more and more attention as a promising technology in biomedical fields. In this work, rare earth ions-doped Ba2LaF7 nanocrystals have been successfully developed by the high-temperature solid-phase method as the core material in a multi-functional system. Optical temperature measurement based on fluorescence intensity ratio improves sensitivity by widely separating Er3+ and Nd3+ emission bands. Meanwhile, the relative sensitivity increases with increasing temperature. From the comparison between the fitting curve and the actual temperature, it can be concluded that the nanocrystals have a good photothermal response to the laser pumping power and can even be used for photothermal imaging. On this basis, to study its optical measurement and photothermal conversion performance, we made a multifunctional system acting on biological tissues. The results suggest that the developed material has a potential application in bio-targeted photothermal therapy.

Laser induced white emission of diamond.

Laser-induced white emission of diamond was investigated under irradiation with a focused beam of an infrared laser diode. It is a surface-related coherent emission, characterized by an excitation threshold and an exponential dependence on pumping laser power. The mechanism of white emission is discussed in terms of multiphoton ionization of carbon atoms in an irradiated spot. The excitation power dependence of white emission intensity has demonstrated hysteresis loop behavior. This phenomenon could be useful in new broadband laser sources and optical information storage.

Broadband flat amplification based on fully double-pass configuration in serial hybrid fiber amplifier

A broadband amplification that utilizes a serial hybrid fiber amplifier is experimentally demonstrated in this paper. Two fully double-pass configurations, namely, setups A and B, are implemented. The difference between these two configurations is that the position of the two amplifiers (erbium and Raman) is swapped. These two configurations are tested under the same input parameter conditions. Two laser pump power wavelengths with a total pump power of 375 mW (1495 nm with 350 mW for Raman and 1480 nm with 25 mW for the erbium amplifier) were used. Under the optimum condition and under a small signal power of −30 dBm, a wide flatness gain bandwidth of 80 nm (1530–1610 nm) with an average gain level of 28.5 and 24 dB is achieved for setups A and B, respectively. A wide bandwidth is achieved by avoiding the amplification overlap between these two amplifiers through choosing the proper pump wavelength. In addition, A gain dynamic range values of 3 dB and more than 15 dB were recorded for setup A and B respectively.

Time-resolved serial femtosecond crystallography on fatty-acid photodecarboxylase: lessons learned.

Upon absorption of a blue-light photon, fatty-acid photodecarboxylase catalyzes the decarboxylation of free fatty acids to form hydrocarbons (for example alkanes or alkenes). The major components of the catalytic mechanism have recently been elucidated by combining static and time-resolved serial femtosecond crystallography (TR-SFX), time-resolved vibrational and electronic spectroscopies, quantum-chemical calculations and site-directed mutagenesis [Sorigué et al. (2021), Science, 372, eabd5687]. The TR-SFX experiments, which were carried out at four different picosecond to microsecond pump-probe delays, yielded input for the calculation of Fourier difference maps that demonstrated light-induced decarboxylation. Here, some of the difficulties encountered during the experiment as well as during data processing are highlighted, in particular regarding space-group assignment, a pump-laser power titration is described and data analysis is extended by structure-factor extrapolation of the TR-SFX data. Structure refinement against extrapolated structure factors reveals a reorientation of the generated hydrocarbon and the formation of a photoproduct close to Cys432 and Arg451. Identification of its chemical nature, CO2 or bicarbonate, was not possible because of the limited data quality, which was assigned to specificities of the crystalline system. Further TR-SFX experiments on a different crystal form are required to identify the photoproducts and their movements during the catalytic cycle.

Crystallization via cavity-assisted infinite-range interactions

We study a one-dimensional array of bosons with infinite-range interactions mediated by a laser-driven dissipative optical cavity. The cavity-mediated infinite-range interactions open up a new pathway to fermionization, hitherto only known for dipolar bosons due to their long-range interactions. In parameter ranges attainable in state-of-the-art experiments, we systematically compare observables for bosons and fermions with infinite-range interactions. At large enough laser pump power, many observables, including density distributions in real and momentum space, correlation functions, eigenvalues of the one-body density matrix, and superradiance order parameter, become identical for bosons and fermions. We map out the emergence of this cavity-induced fermionization as a function of pump power and contact interactions. We discover that cavity-mediated interactions can compensate a reduction by several orders of magnitude in the strength of the contact interactions needed to trigger fermionization.

Recovery of the laser-induced breakdown spectroscopy system using a ceramic microchip deteriorated by radiation for the remote elemental analysis

ABSTRACT The radiation-induced deterioration of ceramic microchip laser properties limits the applications of laser-induced breakdown spectroscopy (LIBS) systems. The deteriorated properties were recovered through thermal treatment of ceramics as derived by the spectroscopic comparison of ceramics and single crystals (SCs). The absorption in spectra was increased by gamma rays irradiation, which was higher for the ceramics than for the SCs in the infrared radiation region. Although the amount of absorption decreased by heating and increased via cooling ceramics, no significant thermal effects were observed for the SCs. The effects of irradiation on the laser properties of ceramics were examined, and the laser pulse energy loss was well recovered via heating. Because heating did not deteriorate the beam profile, affecting the LIBS efficiency, the procedure was effective in recovering the diminished LIBS signal. Although heating reduced the number of generated pulses, affects the burst-mode measurement, the reduction was recovered by increasing the pump laser power. Because the radiation-induced deterioration of the LIBS signal for single-pulse and multiburst mode measurements was well recovered, the procedures are considered effective for the application of LIBS systems using radiation-sensitive ceramics, particularly in harsh radiation environments.