Excited State Absorption Transition Research Articles

Excited state absorption in Yb 3+–Er 3+-codoped phosphate glasses (ZnO–Al 2O 3–La 2O 3–P 2O 5) around the 4I 13/2→ 4I 15/2 emission spectral range

We are involved in Yb 3+–Er 3+-codoped phosphate glass research for eye-safe laser source near 1540 nm. Undoped and doped glasses of the composition: ZnO–Al 2O 3–La 2O 3–P 2O 5 have been synthesised. Absorption from the 4I 15/2 ground state, emission spectra and decay time measurements have been performed at room temperature on these materials. In addition to the usual spectroscopic characterisations, the excited state absorption 4I 13/2→ 4I 9/2 Er 3+ transition located at the long wavelength edge of the 4I 13/2→ 4I 15/2 emission transition have also been investigated at room temperature. The excited state absorption spectra were obtained with a pump and probe technique employing a double modulation scheme in the infrared wavelength region from 1300 to 1900 nm. Furthermore, the line strength of the excited state absorption transition have been calculated in order to compare it with the experimental.

Excited state absorption and stimulated emission of Nd 3+ in crystals. Part I: Y 3 Al 5 O 12 , YAlO 3 , and Y 2 O 3

F3/2 excited state of the Nd3+ ion in Y3Al5O12, YAlO3, and Y2O3 were measured in a continuous wave pump- and probe experiment in a wide spectral range from 850 nm (780 nm for Y3Al5O12) to 1500 nm. The cross sections were determined from a comparison with the emission spectra and the simultaneously measured ground state absorption bleaching. The strongest excited state absorption transitions were found in the 1220–1400 nm spectral region due to transitions to the 2G9/2 and 4G7/2 levels. The spectral positions of the measured transitions are in good agreement with the theoretically expected transitions calculated from the known Stark-level splittings.

Upconversion fluorescence of Ho 3+ ions in a BaF 2 crystal

Efficient upconversion luminescence from the Ho 3+ C 3v centre in a BaF 2 crystal is reported. The red-to-green and red-to-blue upconversion is observed upon pumping with a single cw red dye laser. The upconversion mechanism is assigned as a sequential two-photon excitation process in which the excitation wavelength is resonant with either ground state absorption (GSA) or excited state absorption transitions. The efficient green upconversion with excitation into GSA results from a double-resonant excitation between the 5I 8→ 5F 5 and 5I 7→ 5F 3 transitions.

Optical transitions inMn3+-doped garnets

The optical spectra of ${\mathrm{Mn}}^{3+}$-doped garnet crystals reveal a large Jahn-Teller stabilization energy of about $1900{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for the ${}^{5}E$ ground state, and smaller Jahn-Teller stabilization energies for the excited states, i.e., $\ensuremath{\approx}325{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for the ${}^{5}{T}_{2},$ and $\ensuremath{\approx}180{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for the ${}^{1}{T}_{2}$ level. The absorption spectra are dominated by the spin-allowed ${}^{5}{E}^{5}{T}_{2}$ transition. At low temperatures, the emission occurs from the ${}^{1}{T}_{2}$ level to the Jahn-Teller-split ground state and the ${}^{3}{T}_{1}$ intermediate level. With increasing temperature the ${}^{5}{T}_{2}$ level becomes thermally populated and the emission spectrum is dominated by the spin-allowed ${}^{5}{\stackrel{\ensuremath{\rightarrow}}{{T}_{2}}}^{5}E$ transition. The emission lifetime is nearly independent of the detection wavelength, but strongly dependent of the temperature and the host lattice. At 12 K the lifetime is $\ensuremath{\approx}6\mathrm{ms}$ for all crystals, while at room temperature it is between 1.1 ms for ${\mathrm{Mn}}^{3+}{:\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ and $<0.5\ensuremath{\mu}\mathrm{s}$ for ${\mathrm{Mn}}^{3+}{:\mathrm{G}\mathrm{d}}_{3}{\mathrm{Sc}}_{2}{\mathrm{Ga}}_{3}{\mathrm{O}}_{12}.$ The radiative lifetimes of the ${}^{1}{T}_{2}$ and ${}^{5}{T}_{2}$ levels were determined to be about 6 ms and 16 \ensuremath{\mu}s, respectively. Both the radiative and the nonradiative rate are temperature dependent due to the coupling of odd-parity and totally-symmetric phonons, and the thermalization of the ${}^{5}{T}_{2}$ level. The nonradiative decay is more pronounced for lower crystal-field strengths, because of the smaller ${}^{5}{T}_{2}{\ensuremath{-}}^{3}{T}_{1}$ energy gap and the higher population of the ${}^{5}{T}_{2}$ level. Excited-state absorption transitions arising from the energetically lower ${}^{1}{T}_{2}$ in higher lying singlet levels cover the entire spectral range of the emission; therefore laser oscillation at room temperature is unlikely in ${\mathrm{Mn}}^{3+}$-doped garnets.

Excited-state absorption and laser potential of Mn^6+-doped BaSO_4 crystals

Room-temperature E‖b and E⊥b polarized excited-state absorption (ESA) measurements on Mn6+-doped crystals of BaSO4 in the 530–1800-nm spectral region are reported. ESA transitions from the metastable 2T2 ligand–field state to the lowest-energy ligand-to-metal charge transfer states involve two-electron excitations and thus carry low intensity. A strong ESA band owing to the first one-electron ligand-to-metal charge transfer transition peaks near 600 nm. Between 700 and 900 nm, ground-state absorption is stronger than ESA, and near-infrared pumping by laser diodes is thus possible. The stimulated-emission cross section is larger than the ESA cross section over the whole range of spontaneous emission. Our results indicate that tunable laser action between 920 nm and 1.6 µm should, in principle, be achievable. The effective peak stimulated-emission cross section at 1100 nm is 3×10-19 cm2.

Three-photon upconversion in Er 3+ doped Ca 3Al 2Ge 3O 12

Efficient upconversion fluorescence from an Er 3+ center in Ca 3Al 2Ge 3O 12 has been observed, upon pumping with a single red dye laser. The mechanism for the blue upconversion is either a sequential three-photon absorption or an energy transfer process depending on the laser energy being tuned on either the excited state absorption or the ground state absorption transitions. Owing to a double resonant excited state absorption transition character, the three-photon blue upconversion efficiency is relatively high.

Ultrafast absorption difference spectra of the Fenna-Matthews-Olson protein at 19 K: experiment and simulations

We describe simulations of absorption difference spectra in strongly coupled photosynthetic antennas. In the presence of large resonance couplings, distinctive features arise from excited-state absorption transitions between one- and two-exciton levels. We first outline the theory for the heterodimer and for the general N-pigment system, and we demonstrate the transition between the strong and weak coupling regimes. The theory is applied to Fenna-Matthews-Olson (FMO) bacteriochlorophyll a protein trimers from the green photosynthetic bacterium Prosthecochloris aestuarii and then compared with experimental low-temperature absorption difference spectra of FMO trimers from the green bacterium Chlorobium tepidum.

Ultrafast dynamics of excited-state absorption in V3+:YAG crystal

Picosecond differential absorption spectra measurements for V3+:YAG were performed and a schematic energy-level diagram for tetrahedrally coordinated V3+ in YAG was deduced. The excited-state absorption transitions from the 1E(1D) level were observed with peaks at 870 and 740 nm. The lifetime of the 1E(1D) excited state of the tetrahedral V3+ was found to be ∼130 ps. The ground-state absorption band of the 3T1(3P) state was found to be at 590 nm.

IR-to-visible up-conversion mechanisms in Pr 3+-doped ZBLAN fluoride glasses and fibers

The infrared-to visible up-conversion in Pr 3+-doped ZBLAN fluoride glasses has been investigated for different activator concentrations and for different type-materials, either bulk or fiber. Single beam experiments using continuous wave (CW) laser excitation and pulsed laser excitation allow to point out different up-conversion mechanisms, namely excited state absorption (ESA) and energy transfer up-conversion (ETU). The 2.8th power dependence of the blue fluorescence from the 3P 0 state under CW resonant pumping of the 1G 4 state indicates a dominant three-photon mechanism involving the 1D 2 state. Pulsed laser excitation shows that an ETU process is occurring. When the excitation wavelength is resonant with an ESA transition from the 1G 4 state, a two-photon process is pointed out. Concerning the red fluorescence issued from 1D 2 state, under CW excitation of the 1G 4 state, it is attributed to an ETU process which is greatly enhanced by ESA of the 1.3 μm signal, in the amplification regime in fibers. The influence of the Stark splitting and subsequent transition probabilities on the optical spectra is discussed, enlightening a behavior particular to Pr 3+ ion as compared to other rare earth ions.

Room-temperature up-conversion fluorescence of rare-earth centers in CaF 2

We report temperature-dependent up-conversion fluorescence from Er 3+ and Tm 3+ C 4v centers in CaF 2, upon pumping with a single red-dye laser. The up-conversion mechanism is a sequential two-photon excitation process in which the laser is resonant with either a ground-state or an excited-state absorption transition.

Up-conversion fluorescence of Eu 3+ doped alkaline earth fluoride crystals

Up-converted fluorescence has been observed for single laser frequency excitation of Eu 3+ ions in the tetragonal C 4v(F −) center of CaF 2 and SrF 2 and for the trigonal C 3v(F −) center of BaF 2. Numerous up-converted transitions are observed for resonant excitation of the long-lived 5D 0 multiplet, in addition to resonant excitation of excited state absorption transitions.

Study of closed-shell molecular complexes as possible laser media

We have evaluated a series of blue-green emitting molecular-complex materials (d/sup 0/ electronic system) from the point of view of their suitability as possible tunable laser media. All of them reveal a very strong, broad-band excited-state absorption (ESA), occurring between states of different configurations and positioned at the energy related to the crystal field parameter 10 Dq. The ESA strongly overlaps the luminescence spectra. Because of the nature of the terminal state of ESA, the high rate of ESA transitions can be ascribed to the efficient breaking of the Laporte selection rule, because of considerable admixture of % orbitals of ligands and/or p-orbitals of the central ion into the d-orbitals of the central ion in the terminal configuration, and to the existence of triplet terms in this configuration. We survey the ESA characteristics and compare its cross sections to those of stimulated emission. We interpret the obtained results by means of a configuration-coordinate model. Some possible avenues of future work are indicated. >

Excited-state absorption in Pr3+:Y3Al5O12.

The optical-absorption transitions originating from the lowest 4f5d excited state of ${\mathrm{Pr}}^{3+}$ in ${\mathrm{Y}}_{3}$${\mathrm{Al}}_{5}$${\mathrm{O}}_{12}$ have been studied. The experimental arrangement uses a 7-ns 266-nm light pulse to populate the lowest 4f5d state, and a spatially overlapped, time-sequenced pulse from a frequency-tunable dye laser to induce transitions from that excited state. The excited-state-absorption (ESA) spectrum covering the 900--300-nm probe wavelength range is characterized by two broad peaks centered at 700 and 350 nm on a slowly rising background. The peak ESA cross section at 355 nm is (1\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}17}$ ${\mathrm{cm}}^{2}$. The position, shape, and strength of the spectrum suggest that the terminal states of the ESA transitions are the second 4f5d state of ${\mathrm{Pr}}^{3+}$ and the conduction band of the host lattice. The ESA measurements have been extended to transitions from the $^{3}$${\mathit{P}}_{0}$ and $^{1}$${\mathit{D}}_{2}$ excited states of the 4${\mathit{f}}^{2}$ configuration of ${\mathrm{Pr}}^{3+}$ as well. The ESA cross sections at a probe wavelength of 532 nm are (8\ifmmode\pm\else\textpm\fi{}1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}19}$ ${\mathrm{cm}}^{2}$ and (5.7\ifmmode\pm\else\textpm\fi{}0.6)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}19}$ ${\mathrm{cm}}^{2}$ for transitions from the $^{3}$${\mathit{P}}_{0}$ and $^{1}$${\mathit{D}}_{2}$ excited states, respectively. The terminal state of ESA transitions from these two levels is the lowest 4f5d state. The strong ESA completely inhibits the potential laser action based on emission from these states in this crystal.

Excited-state absorption in ZnWO 4 crystal

We report the first measurement of Excited-State Absorption (ESA) in a zinc tungstate (ZnWO 4) crystal. The ESA is assigned to the 2e→4t 2 transitions and, in the simplest picture, can be related to the 10 Dq energy in T d symmetry. The breadth and height of the ESA spectrum, compared with stimulated emission spectrum, precludes any possibility of laser action in this material. The very high strength of ESA transitions suggests a triplet character of the terminal ESA term, originating in (t 5 1,4t 2) configuration, and breaking the Laporte selection rule. The latter is consistent with considerable contribution of p-orbitals of the ligands and the tungsten ion in the terminal ESA state.

Excited-state absorption of Pr3+-doped fluoride crystals

The absorption and emission properties of the 4f-5d transition of trivalent praseodymium in fluoride crystals have been characterized, including the CaF 2 , SrF 2 , LiYF 4 and BaY 2 F 8 hosts. The emmission from the 4f5d state to numerous 4f 2 levels is observed, and the emission decay time is in the range of 25–29 ns. Attempts to measure gain on the 5d→4f transition have been unsuccessful, as a consequence of an interfering excited state absorption transition due to and electronic transition from the 5d orbital to the conduction band of the host.

Excited-state absorption in BaY2F8:Nd3+

Upconversion pumping with yellow cw and pulsed dye lasers was used to produce uv and blue light arising from deexcitation of the $^{4}$${\mathit{D}}_{3/2}$ and $^{2}$${\mathit{P}}_{3/2}$ states of ${\mathrm{Nd}}^{3+}$ ions in ${\mathrm{BaY}}_{2}$${\mathrm{F}}_{8}$:${\mathrm{Nd}}^{3+}$. Upconversion excitation occurs via sequential two-photon absorption, which was probed by the anti-Stokes emission dynamics and by a two-color laser experiment. An analysis of the steady-state populations as a function of pumping rates ${\mathit{R}}_{1}$ and ${\mathit{R}}_{2}$ for the two-step excitation is developed. When the excitation frequency is resonant with the $^{4}$${\mathit{F}}_{3/2}$${\ensuremath{\rightarrow}}^{4}$${\mathit{D}}_{3/2}$ excited-state absorption transition, the power dependence of the anti-Stokes fluorescence intensity, plotted on a logarithmic scale, shows a straight line with a slope of 1.8. This behavior is explained quite well by the model for a mean-excitation-power regime where the second step is 4 orders of magnitude more efficient than the ground-state absorption.

Excited-state absorption in excimer-pumped CaWO 4 crystals

We report excited state absorption (ESA) in a CaWO 4 under excimer laser excitation (308 nm). The ESA spectrum proves to be very broad and intense. We calculate the stimulated emission cross-section and show that it is at least one order of magnitude smaller than the broad-band ESA cross-section. This precludes laser action in an undoped CaWO 4 crystal. The ESA spectra can be assigned to the transitions between terms of (t 5 1, 2e) and (t 5 1, 4t 2) configurations of the WO 2- 4 complex. Using experimental parameters deduced from the emission and ESA spectra, we construct a configuration coordinate diagram including a higher excited state. The diagram predicts that the initial and terminal states of the ESA transition are characterized by different equilibrium positions and, consequently, different charge distribution. It is suggested that this effect can be explained by contribution of p orbitals of the ligand ions to the 4t 2 state. The overall ESA is of a complex nature, being a combination of conventional ESA, decaying like luminescence and another, long lasting component possibly connected with phosphorescent traps. This behavior is reproduced by a simple kinetic model.

New excited-state absorption measurement technique and application to Pr3+ doped fluorozirconate glass

A new technique for analyzing excited state absorption (ESA) is introduced, in which the relative ESA spectrum is determined directly from fluorescence measurements. This represents, to our knowledge, the first application of the McCumber theory [D. E. McCumber, Phys. Rev. 136, A954 (1964)] to the calculation of excited state absorption spectra. The new technique is used to study ESA transitions from the 1G4 level in Pr3+ doped fluoride glass (ZBLAN). An ESA transition around 1380 nm is found, which shifts the peak of the gain curve for a 1.3 μm Pr3+ fiber amplifier about 10 nm to shorter wavelengths, and gives rise to negative gain for wavelengths longer than 1380 nm. Another ESA transition around 840 nm is found, which is an order of magnitude stronger than the 1 μm ground state absorption.

Excited-state absorption cross sections in the 800-nm band for Er-doped, Al/P-silica fibers: Measurements and amplifier modeling

Excited-state absorption (ESA) cross sections were determined for the 800-nm band of Er-doped, Al/P-silica fibers. The oscillator strength of the ESA transition exceeds that of the 800 nm, ground-state absorption (GSA) transition by a factor of approximately= 2.3, in reasonable agreement with a Judd-Ofelt calculation. The extended, long-wavelength tail of the GSA band leads to a region around 820 nm where the GSA cross section approximately= ESA cross section. The cross sections were incorporated into an amplifier model for pumping in the 800-nm band. Codirectional and the bidirectional pumping schemes were analyzed for excitation near the peak and in the long wavelength tail of the GSA band. Pumping in the tail for either pumping scheme or pumping near the peak for the bidirectional scheme are predicted to produce a significant improvement in the small-signal gain.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The role of excited-state absorption in tunable solid-state lasers

The lasing properties of tunable solid state lasers can be strongly influenced by Excited State Absorption (ESA). It is shown that the tuning behaviour of Cr:GSGG and Cr:LLGG is limited at short wavelengths due to the ESA transitions2E →2T2 (b),2T1 (b) and4T2 →4T1 (b), respectively. At long wavelengths the4T2 →4T1 (a) ESA transition narrows the tuning range largely. The reason is that both levels are Jahn-Teller split due to the centric chromium site resulting in a very broad ESA band. In Ti: YAIO3 strong ESA of the pumping wavelength into a charge transfer band occurs, which is caused by a Ti3+/Fe3+ complex centre. By this transition the pumping efficiency is diminished largely. It is believed that the lasing behaviour of Ti: YAIO3 can be improved considerably by growing of highest iron-free crystals.