Indirect Pumping Research Articles

Quantum sized Ag nanocluster assisted fluorescence enhancement in Tm3+-Yb3+ doped optical fiber beyond plasmonics

We report a process for enhancing fluorescence emission from conventional rare earth ions in optical fiber by metal nanocluster (MNC) in nonresonant indirect pumping. The process is completely different from formal metal enhanced fluorescence phenomenon as the MNCs are too small in size to support localized surface plasmon and the excitation wavelength is far from plasmon resonance frequency. We used an established theory of two coupled oscillators to explain the simultaneous enhancement of Ytterbium (Yb3+) and Thulium (Tm3+) emission by silver (Ag) NCs under nonresonant pumping in optical fiber. The fiber is pumped with a 980 nm fiber pigtailed laser diode with input power of 20–100 mW to excite the Yb3+. Four times enhancement of Yb3+ emission of 900–1100 nm and Tm3+ upconversion emission around 474 nm, 650 nm, and 790 nm is observed in the fiber with Ag NCs.

Alkali-Metal Spin Maser

Quantum measurement is a combination of a read-out and a perturbation of the quantum system. We explore the nonlinear spin dynamics generated by a linearly polarized probe beam in a continuous measurement of the collective spin state in a thermal alkali-metal atomic sample. We demonstrate that the probe-beam-driven perturbation leads, in the presence of indirect pumping, to complete polarization of the sample and macroscopic coherent spin oscillations. As a consequence of the former we report observation of spectral profiles free from collisional broadening. Nonlinear dynamics is studied through exploring its effect on radio frequency as well as spin noise spectra.

Amplitude-modulated indirect pumping of spin orientation in low-density cesium vapor

A recently demonstrated technique of continuous indirect pumping enables a high level of atomic spin polarization to be generated in thermal alkali-metal vapors, without compromising the coherence lifetime through power broadening from the pump laser. The indirect pumping process combines optical excitation and spin-exchange collisions. Here we describe the pumping process and the role of spin-exchange collisions for the case of amplitude-modulated optical excitation. We demonstrate that effective spin-exchange decoherence is modified by the measurement geometry and dynamics. Decoherence changes are studied through magneto-optical-rotation signals. The studies presented here are particularly important for optimizing the performance of an atomic magnetometer operating in the quantum nondemolition configuration in a nonzero-magnetic-field environment.

Organic–inorganic heterostructures for nonlinear optics

We consider a hybrid heterostructure made of an inorganic quantum well in close proximity with an organic material overlayer, whereby the latter is used to funnel excitation energy to the former in order to exploit the optical nonlinearities of the two-dimensional Wannier excitons. The resonant optical pumping of the Frenkel excitons and their diffusion to the organic–inorganic interface can lead to an efficient indirect pumping of the inorganic quantum well turning on the corresponding nonlinearities. As organic material we consider a layer of anthracene or of tetracene. In the latter case, the singlet exciton has an energy which is close to twice the one of a triplet exciton and singlet exciton fission into two triplets can be efficient. In tetracene based hybrid heterostructures, the temperature dependence of fission opens the possibility to turn on and off the indirect pumping due to energy transfer from the organic into the inorganic subsystem. Finally, we show how a generic mechanism of dipole–dipole hybridization may lead to the formation of virtual heterodimers of organic molecules with an enhanced nonlinear optical response.

Roles of semiquinone species in proton pumping mechanism by complex I.

Complex I (NDH-1) translocates protons across the membrane using electron transfer energy. Two different coupling mechanisms are currently being discussed for complex I: direct (redox-driven) and indirect (conformation-driven). Semiquinone (SQ) intermediates are suggested to be key for the coupling mechanism. Recently, using progressive power saturation and simulation techniques, three distinct SQ species were resolved by EPR analysis of E. coli complex I reconstituted into proteoliposomes. The fast-relaxing SQ (SQ(Nf)) signals completely disappeared in the presence of the uncoupler gramicidin D or the potent E. coli complex I inhibitor squamotacin. The slow-relaxing SQ (SQ(Ns)) signals were insensitive to gramicidin D, but they were sensitive to squamotacin. The very slow-relaxing SQ (SQ(Nvs)) signals were insensitive to both gramicidin D and squamotacin. Interestingly, no SQ(Ns) signal was observed in the ΔNuoL mutant, which lacks transporter module subunits NuoL and NuoM. Furthermore, we sought out the effect of using menaquinone (which has a lower redox potential compared to that of ubiquinone) as an electron acceptor on the proton pumping stoichiometry by in vitro reconstitution experiments with ubiquinone-rich or menaquinone-rich double knock-out membrane vesicles, which contain neither complex I nor NDH-2 (non-proton translocating NADH dehydrogenase). No difference in the proton pumping stoichiometry between menaquinone and ubiquinone was observed in the ΔNuoL and D178N mutants, which are considered to lack the indirect proton pumping mechanism. However, the proton pumping stoichiometry with menaquinone decreased by half in the wild-type. The roles and relationships of SQ intermediates in the coupling mechanism of complex I are discussed.

Struktur und Funktion der mitochondrialen Atmungskettenkomplexe

The molecular mechanisms of redox driven proton pumps are surprisingly diverse. Studying them is a great challenge, since protons are also involved in acid/base equilibria and many other redox reactions. Indirect pumping by long range interactions in complex I, ligand conduction via bifurcated electron transfer in complex III and direct proton pumping combined with charge translocation by an incomplete redox loop in complex IV are found in the respirasomes of the mitochondrial respiratory chain.

Singlets and triplets in hybrid nanodevices

An organic material thin layer can be used to resonantly absorb light and nonradiatively transfer excitation to an adjacent inorganic quantum well the optical nonlinearities of which can in this way be turned on more efficiently than by direct optical pumping. We theoretically consider this process in a hybrid structure based on crystalline tetracene in which the singlet exciton energy is close to twice the one of a triplet exciton and thermally activated singlet exciton fission into two triplets can be efficient. We investigate how the temperature dependence of the singlet exciton diffusion length affects the functional properties of such hybrid organic-inorganic nanostructures based on tetracene. We show how temperature activated fission opens a new possibility to turn on and off the indirect pumping due to energy transfer from the organic into the inorganic subsystem.

Excited state Faraday anomalous dispersion optical filters based on indirect laser pumping

The direct pump method now used in excited state Faraday anomalous dispersion optical filters (ES-FADOFs) requires that the transition between the target and the ground state is an electric dipole allowed transition and that a laser that operates at the exact pump wavelength is available. This is not always satisfied in practice. An indirect laser pump method for ES-FADOF is proposed and experimentally realized. Compared with the commonly used direct pump method, this indirect pump method can reach the same performance using lasers at very different wavelengths. This method can greatly extend the wavelength range of FADOF and provide a novel scheme for ES-FADOF design.

Effect of pump wavelength on Nd^3+:YABself-frequency-doubling laser

The direct and indirect pumping could be used to excite Nd3+-activated crystals effectively. The advantage of direct pumping is the reduction of heat load, and the shortage is the low absorption of pump power. They are the contrary factors affecting the laser performance; hence, the direct pumping is not always better than indirect pumping. To compare the laser performance under direct pumping with that under indirect pumping, the self-frequency-doubling laser model that takes the heat load into account is developed, and the model is applied to the case of Nd3+:YAB crystal. For the typical experimental parameters, we derive the criteria to judge the preferential pumping for the given crystal.

Efficient optical pumping of organic-inorganic heterostructures for nonlinear optics

We theoretically consider a hybrid heterostructure made of an inorganic quantum well in close proximity with an organic material overlayer whereby the latter is used to funnel excitation energy to the former in order to exploit the optical nonlinearities of the two-dimensional Wannier excitons. On the one hand, the diffusion length of Frenkel excitons in the organic medium is assumed to be comparable or larger than the corresponding absorption length. On the other hand, the nonradiative energy transfer from the organic to the inorganic subsytem can be very efficient when the Frenkel exciton energy is significantly higher than the band gap of the inorganic semiconductor. We show in this regime that the resonant optical pumping of the Frenkel excitons can lead to an efficient indirect pumping of the Wannier excitons (or electron-hole plasma) in the inorganic quantum well turning on the corresponding nonlinearities.

Room temperature femtotesla radio-frequency atomic magnetometer

A radio-frequency tunable atomic magnetometer with a sensitivity of about 1 fT/Hz1/2 in a range of 10–500 kHz is demonstrated. The magnetometer is operated in the orientation configuration in which atoms are pumped to the stretched atomic state by a scheme based on indirect optical pumping using only one unmodulated, low-power laser. The magnetometer operates with cesium atoms, which have sufficient vapor pressure near room temperature to enable high magnetometric sensitivities. The technique enables a compact and robust module to be constructed that could become an in-the-field device.

Synthesis, characterization, optical absorption, luminescence and defect centres in Er3+ and Yb3+ co-doped MgAl2O4 phosphors

The Er3+–Yb3+ co-doped MgAl2O4 phosphor powders have been prepared by the combustion method. The phosphor powders are well characterized by X-ray diffraction (XRD) and energy dispersive (EDX) techniques. The absorption spectrum of Er3+/Er3+–Yb3+ doped/co-doped phosphor powder has been recorded in the UV–Vis–NIR region of the electro-magnetic spectrum. The evidence for indirect pumping under 980 nm excitation of Er3+ from Yb3+ was observed in the MgAl2O4 matrix material. Electron spin resonance (ESR) studies were carried out to identify the defect centres responsible for the thermally stimulated luminescence (TSL) process in MgAl2O4:Er3+ phosphor. Three defect centres were identified in irradiated phosphor by ESR measurements which were carried out at room temperature and these were assigned to an O− ion and F+ centres. O− ion (hole centre) appears to correlate with the low temperature TSL peak at 210 °C and one of the F+ centres (electron centre) is related to the high temperature peak at 460 °C.

Design of three-well indirect pumping terahertz quantum cascade lasers for high optical gain based on nonequilibrium Green’s function analysis

The nonequilibrium Green’s function approach is applied to the design of three-well indirect pumping terahertz (THz) quantum cascade lasers (QCLs) based on a resonant phonon depopulation scheme. The effects of the anticrossing of the injector states and the dipole matrix element of the laser levels on the optical gain of THz QCLs are studied. The results show that a design that results in a more pronounced anticrossing of the injector states will achieve a higher optical gain in the indirect pumping scheme compared to the traditional resonant-tunneling injection scheme. This offers in general a more efficient coherent resonant-tunneling transport of electrons in the indirect pumping scheme. It is also shown that, for operating temperatures below 200 K and low lasing frequencies, larger dipole matrix elements, i.e., vertical optical transitions, offer a higher optical gain. In contrast, in the case of high lasing frequencies, smaller dipole matrix elements, i.e., diagonal optical transitions are better for achieving a higher optical gain.

Design concepts of terahertz quantum cascade lasers: Proposal for terahertz laser efficiency improvements

Conceptual disadvantages of typical resonant phonon terahertz quantum cascade lasers (THz-QCLs) are analyzed. Alternative designs and their combination within a concrete device proposal are discussed to improve the QCL performance. The improvements are (1) indirect pumping of the upper laser level, (2) diagonal optical transitions, (3) complete electron thermalization, and (4) materials with low effective electron masses. The nonequilibrium Green’s function method is applied to predict stationary electron transport and optical gain. The proposed THz-QCL shows a higher optical gain, a lower threshold current, and a higher operation temperature. Alloy disorder scattering can worsen the QCL performance.

UVES/VLT high resolution absorption spectroscopy of the GRB 080330 afterglow: a study of the GRB host galaxy and intervening absorbers

We study the Gamma Ray Burst (GRB) environment and intervening absorbers by analyzing the optical absorption features produced by gas surrounding the GRB or along its line of sight. We analyzed high resolution spectroscopic observations (R=40000, S/N=3 - 6) of the optical afterglow of GRB080330, taken with UVES at the VLT ~ 1.5 hours after the GRB trigger. The spectrum illustrates the complexity of the ISM of the GRB host galaxy at z = 1.51 which has at least four components in the main absorption system. We detect strong FeII, SiII, and NiII excited absorption lines associated with the bluemost component only. In addition to the host galaxy, at least two more absorbers lying along the line of sight to the afterglow have been detected in the redshift range 0.8 < z < 1.1, each exhibiting MgII absorption. For the bluemost component in the host galaxy, we derive information about its distance from the site of the GRB explosion. We do so by assuming that the excited absorption lines are produced by indirect UV pumping, and compare the data with a time dependent photo-excitation code. The distance of this component is found to be 280+40-50 pc, which is lower than found for other GRBs (1 - 6 kpc). We identify two additional MgII absorbers, one of them with a rest frame equivalent width larger than 1A. The distance between the GRB and the absorber measured in this paper confirms that the power of the GRB radiation can influence the conditions of the interstellar medium up to a distance of at least several hundred pc. For the intervening absorbers, we confirm the trend that on average one strong intervening system is found per afterglow, as has been noted in studies exhibiting an excess of strong MgII absorbers along GRB sightlines compared to quasars.

Laser performance study of mixed vanadate crystals &lt;inline-formula&gt;&lt;math display="inline" overflow="scroll"&gt;&lt;mrow&gt;&lt;mi mathvariant="normal"&gt;Nd&lt;/mi&gt;&lt;mo&gt;:&lt;/mo&gt;&lt;msub&gt;&lt;mi mathvariant="normal"&gt;Y&lt;/mi&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/msub&gt;&lt;msub&gt;&lt;mi mathvariant="normal"&gt;Gd&lt;/mi&gt;&lt;mrow&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;mi&gt;x&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mi mathvariant="normal"&gt;V&lt;/mi&gt;&lt;msub&gt;&lt;mi mathvariant="normal"&gt;O&lt;/mi&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/inline-formula&gt; with direct and indirect pumping

We present, for the first time, comparative studies of laser performance in the mixed vanadate crystals Nd:YxGd1−xVO4 with direct and indirect pumping. A series of mixed vanadate crystals Nd:YxGd1−xVO4 with different yttrium and gadolinium composition ratios but the same Nd3+ dopant level is prepared under the same fabrication processes and their laser performance in the TEM00 mode operation is studied using the same experimental configuration under direct pumping with laser diodes at 880 nm as well as indirect pumping at 808 nm. Remarkable improvement in laser efficiency and maximum achievable output power is achieved under direct 880-nm excitation over indirect 808-nm excitation. The maximum optical slope efficiency in the TEM00 mode operation is 74% with direct 880-nm pumping, which also produces the maximum overall optical-to-optical conversion efficiency of 59%. The maximum attainable laser power is up to 50% higher under direct 880-nm pumping over the more conventional 808-nm pumping. These achieved results provide valuable insight into crystal composition selection and pump schemes for the mixed vanadate crystals, which have the potential to tailor laser parameters through crystal composition engineering.

Indirect pump scheme for quantum cascade lasers: dynamics of electron-transport and very high T0-values

An alternative pump scheme, named indirect pump one is proposed to clarify its own feasibility. The high device performances of 8 microm quantum cascade lasers with cavity lengths of 4 mm and 1.5 mm are demonstrated: low threshold current densities of 2.7 and 3.3 kA/cm2 and maximum output powers of 362 and 50 mW at room temperature, and high T0-values of 243 and 303 K around room temperature. The higher T0-value, 303 K is the highest record ever reported with quantum cascade lasers. The high stability for temperature changes is interpreted in terms of the indirect pumping model.

Absorption free superluminal light propagation in a three-level pump–probe system

We investigate the dispersion and the absorption properties of a weak probe field in a three-level pump–probe atomic system. It is shown that the slope of dispersion changes from positive to negative just with the intensity of the coherent or indirect incoherent pumping fields. It is demonstrated that the absorption free superluminal light propagation is appeared in this system.

Population dynamics of the 3F4 and 3H4 levels in highly-doped Tm3+:ZB(L)AN glasses

Population dynamics of the 3F4 and 3H4 levels in Tm3+ doped ZB(L)AN glasses was studied for Tm3+ concentrations from 0.5 to 12mol%. Fluorescence waveforms from these levels were measured at 1.8μm (3F4) and 800nm (3H4) with both direct and indirect pumping. Decay from the 3F4 level was found to be exponential with non-radiative decay rates proportional to the square of the Tm concentration. This indicated a process of energy migration by diffusion within the excited Tm3+ ions followed by quenching at sites to which the ions could migrate. The decay of the directly pumped 3H4 level exhibited both exponential and non-exponential behavior depending on the concentration. For the lowest concentration (0.5mol%) the decay was exponential, but at concentrations of 1, 2, 4 and 6mol% the decay waveforms were distinctly non-exponential. The non-exponential waveforms could be fitted by the Yokota–Tanimoto model for diffusion of excited donors and dipole–dipole interactions with acceptors. This model produced values for CDD and CDA, the donor–donor and donor–acceptor energy transfer parameters, respectively. At the higher concentrations (8, 10, 12mol%) the waveforms were exponential with decay rates from which the cross-relaxation parameter for the process 3H4, 3H6→3F4, 3F4 was obtained. When the 3F4 level is pumped at 1660nm, the decay of the 3H4 level confirmed the influence of the up-conversion energy transfer process 3F4, 3F4→3H4, 3H6.

Observation of indirect parallel pumping of magneto-elastic modes in layered YIG/GGG structures

In this work we report new experimental results on nonlinear excitation of magnetoelastic (ME) modes in layered YIG/GGG waveguide structures at GHz frequencies, obtained by a guided-wave light scattering technique. It is shown that the fundamental spin-dipole wave (SDW) mode induces a secondary microwave field at double frequency that can efficiently excite shear elastic modes of the structure. The distinctive feature of a mechanism for ME coupling proposed is that it is free from the selection rules and provides continuous excitation of elastic modes within a wide frequency range by means of the standard microstripe line excitation system.