Persistent Spectral Hole Burning Research Articles

In vivo ultrasound modulated optical tomography with a persistent spectral hole burning filter.

We present in vivo ultrasound modulated optical tomography (UOT) results on mice, using the persistent spectral hole burning (PSHB) effect in a Tm3+:YAG crystal. Indocyanine green (ICG) solution was injected as an optical absorber and was clearly identified on the PSHB-UOT images, both in the muscle (following an intramuscular injection) and in the liver (following an intravenous injection). This demonstration also validates an experimental setup with an improved level of performance combined with an increased technological maturity compared to previous demonstrations.

Storage and Reemission of Heralded Telecommunication-Wavelength Photons Using a Crystal Waveguide

Large-scale quantum networks will employ telecommunication-wavelength photons to exchange quantum information between remote measurement, storage, and processing nodes via fibre-optic channels. Quantum memories compatible with telecommunication-wavelength photons are a key element towards building such a quantum network. Here, we demonstrate the storage and retrieval of heralded 1532 nm-wavelength photons using a solid-state waveguide quantum memory. The heralded photons are derived from a photon-pair source that is based on parametric down-conversion, and our quantum memory is based on a 6 GHz-bandwidth atomic frequency comb prepared using an inhomogeneously broadened absorption line of a cryogenically-cooled erbium-doped lithium niobate waveguide. Using persistent spectral hole burning under varying magnetic fields, we determine that the memory is enabled by population transfer into niobium and lithium nuclear spin levels. Despite limited storage time and efficiency, our demonstration represents an important step towards quantum networks that operate in the telecommunication band and the development of on-chip quantum technology using industry-standard crystals.

Deep and persistent spectral holes in thulium-doped yttrium orthosilicate for imaging applications

With their optical wavelength in the near infrared (790-800nm) and their unique spectroscopic properties at cryogenic temperatures, thulium-doped crystals are at the center of many architectures linked to classical signal processing and quantum information. In this work, we focus on Tm-doped YSO, a compound that was left aside in the mid-1990s due to its rather short optical coherence lifetime. By means of time-resolved hole-burning spectroscopy, we investigate the anisotropic enhanced nuclear Zeeman effect and demonstrate deep, sub-MHz, persistent spectral hole burning under specific magnetic field orientation and magnitude. By estimating the experimental parameters corresponding to a real-scale ultrasound optical tomography setup using Tm:YSO as a spectral filter, we validate Tm:YSO as a promising compound for medical imaging in the human body.

Ultrasound-modulated optical tomography in scattering media: flux filtering based on persistent spectral hole burning in the optical diagnosis window.

Ultrasound-modulated optical tomography (UOT) is a powerful imaging technique to discriminate healthy from unhealthy biological tissues based on their optical signature. Among the numerous detection techniques developed for acousto-optic imaging, only those based on spectral filtering are intrinsically immune to speckle decorrelation. This Letter reports on UOT imaging based on spectral hole burning in Tm:YAG crystal under a moderate magnetic field (200G) with a well-defined orientation. The deep and long-lasting holes translate into a more efficient UOT imaging with a higher contrast and faster imaging frame rate. We demonstrate the potential of this method by imaging calibrated phantom scattering gels.

Influence of Silver Nanoparticles Crystallinity on Localized Surface Plasmons Dephasing Times

The dephasing time of localized surface plasmons is a crucial parameter that defines the quality of resonance and achievable electromagnetic field enhancement near metal nanoparticles. Lattice irregularities of as‐deposited supported metal nanoparticles shorten the plasmon dephasing time and degrade the resonance quality. To study the crystallinity influence on the plasmon dephasing time in more detail, silver nanoparticles in the form of a granular film were produced on dielectric substrates via physical vapor deposition in a vacuum chamber. The samples are characterized using Vis–NIR spectroscopy and transmission electron microscopy. The persistent spectral hole burning technique is applied to study the annealing influence on the dephasing time of localized surface plasmons of the particular resonance frequency. After annealing, the improved crystallinity of nanoparticles leads to a twofold dephasing time increase. This conclusion is supported by the electron diffraction patterns. The role of the improved crystallinity among concurrent effects of annealing is discussed.

Fabrication and laser-assisted modification of the Ag particles ensembles supporting quadrupole plasmon oscillations

A combination of physical vapour deposition, thermal annealing and laser irradiation was used to tailoring of the silver nanoparticles array on a quartz substrate. This method for control of optical properties is exploit 355-nm pulsed laser irradiation. Experimental separation of three main overlapped plasmonic modes, dipoles that correspond to parallel and perpendicular oscillations and quadrupole with maximum wavelength at 355 nm, in extinction spectrum of Ag nanoparticles ensembles was demonstrated. It was shown that the laser post-processing of the nanoparticles array in spectral vicinity of the quadrupole band leads to selective ablation of nanometer particles. This process resulted to close-packing of the nanoparticles ensemble on top of the substrate causing, in turn, formation of ‘hot-spots’ and absorptive bands in the near IR range. Using the laser post-processing as persistent spectral hole burning technique, a dephasing time of quadrupole plasmon resonances was experimentally defined for the first time.

Modification of phonon processes in nanostructured rare-earth-ion-doped crystals

Nano-structuring impurity-doped crystals affects the phonon density of states and thereby modifies the atomic dynamics induced by interaction with phonons. We propose the use of nano-structured materials in the form of powders or phononic bandgap crystals to enable or improve persistent spectral hole-burning and coherence for inhomogeneously broadened absorption lines in rare-earth-ion-doped crystals. This is crucial for applications such as ultra-precise radio-frequency spectrum analyzers and optical quantum memories. As an example, we discuss how phonon engineering can enable spectral hole burning in erbium-doped materials operating in the convenient telecommunication band, and present simulations for density of states of nano-sized powders and phononic crystals for the case of Y2SiO5, a widely-used material in current quantum memory research.

Efficient and long-lived Zeeman-sublevel atomic population storage in an erbium-doped glass fiber

Long-lived population storage in optically pumped levels of rare-earth ions doped into solids, referred to as persistent spectral hole burning, is of significant fundamental and technological interest. However, the demonstration of deep and persistent holes in rare-earth ion doped amorphous hosts, e.g. glasses, has remained an open challenge since many decades -- a fact that motivates our work towards a better understanding of the interaction between impurities and vibrational modes in glasses. Here we report the first observation and detailed characterization of such holes in an erbium-doped silica glass fiber cooled to below 1 K. We demonstrate population storage in electronic Zeeman-sublevels of the erbium ground state with lifetimes up to 30 seconds and 80\% spin polarization. In addition to its fundamental aspect, our investigation reveals a potential technological application of rare-earth ion doped amorphous materials, including at telecommunication wavelength.

Free base tetraazaporphine isolated in inert gas hosts: matrix influence on its spectroscopic and photochemical properties.

The absorption, fluorescence, and excitation spectra of free base tetraazaporphine (H2TAP) trapped in Ne, N2, and Ar matrices have been recorded at cryogenic temperatures. Normal Raman spectra of H2TAP were recorded in KBr discs and predicted with density functional theory (DFT) using large basis sets calculations. The vibrational frequencies observed in the Raman Spectrum exhibit reasonable agreement with those deduced from the emission spectra, as well as with frequencies predicted from large basis set DFT computations. The upper state vibrational frequencies, obtained from highly resolved, site selected excitation spectra, are consistently lower than the ground state frequencies. This contrasts with the situation in free base phthalocyanine, where the upper state shows little changes in vibrational frequencies and geometry when compared with the ground state. Investigations of the photochemical properties of H2TAP isolated in the three matrices have been performed using the method of persistent spectral hole-burning (PSHB). This technique has been used to reveal sites corresponding to distinct N-H tautomers which were not evident in the absorption spectra. An analysis of the holes and antiholes produced with PSHB in the Qx (0-0) absorption band made it possible to identify inter-conversion of distinct host sites.

Transient spectral hole burning observed on the single-molecule level in terrylene-doped biphenyl

We use the method of fluorescence correlation spectroscopy to analyze the single-molecule (SM) spectroscopy data earlier recorded for a special type of terrylene SM impurity center (referred as “spectrally confined unstable molecule”, SCM) in an incommensurate single crystal of biphenyl. The SCM's SM line seems to be chaotically jumping around within a broad “spectral envelope” and was first considered being subject to a peculiar spectral diffusion behavior. However, our correlation analysis reveals that all the features observed for SCM at 1.8K are consistent with an assumption that this SM center participates in a process of reversible (transient) spectral hole burning (THB) earlier observed for terrylene-doped polycrystalline biphenyl. No observations of THB processes on SM level have been so far reported for this impurity system, partially due to a low concentration of relevant impurity centers. Another reason making searching for such centers experimentally challenging is an unusual SM line behavior: the photoinduced transition to a metastable “dark state” leads to the SM line saturational broadening, which is much stronger than the triplet broadening. Hence required prolonged observation is often prevented by an SM act of persistent spectral hole burning.

Spectral Hole Burning, Recovery, and Thermocycling in Chlorophyll–Protein Complexes: Distributions of Barriers on the Protein Energy Landscape

Chlorophyll-protein complexes are ideal model systems for protein energy landscape research. Here pigments, used in optical spectroscopy experiments as sensitive probes to local dynamics, are built into protein by Nature (in a large variety of local environments; without extraneous chemical manipulations or genetic engineering). Distributions of the tunneling parameter, λ, and/or protein energy landscape barrier heights, V, have been determined for (the lowest energy state of) the CP43 core antenna complex of photosystem II. We demonstrate that spectral hole burning (SHB) and hole recovery (HR) measurements are capable of delivering important information on protein energy landscape properties and spectral diffusion mechanism details. In particular, we show that tunneling rather than barrier hopping is responsible for both persistent SHB and subsequent HR at 5-12 K, which allows us to estimate the md(2) parameter of the tunneling entities as ~1.0 × 10(-46) kg·m(2). The subdistributions of λ actually contributing to the nonsaturated spectral holes (and affecting their recovery) differ from the respective full true distributions. In the case of the full λ-distribution being uniform (or the barrier height distribution ~1/√V, a model which has been widely employed in theories of amorphous solids at low temperatures and in HR analysis), the difference is qualitative, with λ subdistributions probed in the HR experiments being highly asymmetrical, and barrier V subdistributions deviating significantly from ~1/√V. Thus, the distribution of λ for the protein energy landscape tier directly probed by SHB is likely Gaussian and not uniform. Additionally, a Gaussian distribution of barriers, with parameters incompatible with those of the landscape tier directly probed by SHB, contributes to the thermocycling results.

Electronic spectroscopy, stimulated emission, and persistent spectral hole burning of cryogenic nitrogen matrices doped with tetrabenzoporphin

This paper deals with our on-going work on the electronic spectroscopy of tetrapyrrole molecules embedded in cryogenic hosts. Under nanosecond laser excitation of free-base tetrabenzoporphin molecules in a nitrogen matrix at 8 K, increasing laser pulse energy results in essential enhancement of the intensity of one or several vibronic emission lines in the fine-structure fluorescence spectrum. Some characteristics of stimulated radiation are realized in the observed intense monochromatic radiation as a result of a transition from the purely electronic S1 level to a vibrational sublevel of the S0 state, corresponding to the excitation of C–C stretching vibrations of tetrapyrrole methane bridges. We also report on persistent spectral hole-burning effects. Hole and antihole formation analysis gives some insight on the photochemical properties of tetrabenzoporphin in a nitrogen matrix.

Ultrafast dephasing of localized surface plasmons in colloidal silver nanoparticles: the influence of stabilizing agents

Localized surface plasmon dephasing times for aqueous colloidal silver nanoparticles (NPs) stabilized with three different capping agents (trisodium citrate—TSC, poly(vinylpyrrolidone)—PVP, and poly(vinylalcohol)— PVA) were measured using the persistent spectral hole burning technique. The results obtained by fitting a theoretical curve to the experimental data show that the dephasing times are dependent on the chosen stabilizer (3.0, 2.3, and 1.8 fs for TSC, PVP, and PVA, respectively), and the differences are attributed to changes in the electronic density of states due to the interaction between the NPs and the capping agents. The results are supported by ab initio calculations for the chemisorbate and metallic cluster interaction.

Photoinduced Electron Transfer and Persistent Spectral Hole-Burning in Natural Emerald

Wavelength-selective excited-state lifetime measurements and absorption, luminescence, and hole-burning spectra of a natural African emerald crystal are reported. The (2)E excited-state lifetime displays an extreme wavelength dependence, varying from 190 to 37 μs within 1.8 nm of the R(1)-line. Overall, the excited state is strongly quenched, in comparison to laboratory-created emerald (τ=1.3 ms), with an average quenching rate of ∼6 × 10(3) s(-1) at 2.5 K. This quenching is attributed to photoinduced electron transfer caused by a relatively high concentration of Fe(2+) ions. The forward electron-transfer rate, k(f), from the nearest possible Fe(2+) sites at around 5 Å is estimated to be ∼20 × 10(3) s(-1) at 2.5 K. The photoreductive quenching of the excited Cr(3+) ions by Fe(2+) is followed by rapid electron back-transfer in the ground state upon deactivation. The exchange interaction based quenching can be modeled by assuming a random quencher distribution within the possible Fe(2+) sites with the forward electron-transfer rate, k(f), given as a function of acceptor-donor separation R by exp[(R(f)-R)/a(f)]; R(f) and a(f) values of 13.5 and 2.7 Å are obtained at 2.5 K. The electron transfer/back-transfer reorganizes the local crystal lattice, occasionally leading to a minor variation of the short-range structure around the Cr(3+) ions. This provides a mechanism for spectral hole-burning for which a moderately high quantum efficiency of about ∼0.005% is observed. Spectral holes are subject to spontaneous hole-filling and spectral diffusion, and both effects can be quantified within the standard two-level systems for non-photochemical hole-burning. Importantly, the absorbance increases on both sides of broad spectral holes, and isosbestic points are observed, in accord with the expected distribution of the "photoproduct" in a non-photochemical hole-burning process.

Excitonic Energy Level Structure and Pigment−Protein Interactions in the Recombinant Water-Soluble Chlorophyll Protein. II. Spectral Hole-Burning Experiments

Persistent spectral hole burning at 4.5 K has been used to investigate the excitonic energy level structure and the excited state dynamics of the recombinant class-IIa water-soluble chlorophyll-binding protein (WSCP) from cauliflower. The hole-burned spectra are composed of four main features: (i) a narrow zero-phonon hole (ZPH) at the burn wavelength, (ii) a number of vibrational ZPHs, (iii) a broad low-energy hole at ~665 and ~683 nm for chlorophyll b- and chlorophyll a-WSCP, respectively, and (iv) a second satellite hole at ~658 and ~673 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. The doublet of broad satellite holes is assigned to an excitonically coupled chlorophyll dimer. The lower-energy holes at ~665 and ~683 nm for chlorophyll b- and chlorophyll a-WSCP, respectively, represent the lower exciton states. Taking into account the parameters of electron-phonon coupling, the lower exciton state can be assigned as the fluorescence origin. The lower exciton state is populated by two processes: (i) exciton relaxation from the higher exciton state and (ii) vibrational relaxation within the lower exciton state. Assuming identical site energies for the two excitonically coupled chlorophyll molecules, the dipole-dipole interaction energy J is directly determined to be 85 and 100 cm(-1) for chlorophyll b- and chlorophyll a-WSCP, respectively, based on the positions of the satellite holes. The Gaussian low-energy absorption band identified by constant fluence hole burning at 4.5 K has a width of ~150 cm(-1) and peaks at 664.9 and 682.7 nm for chlorophyll b- and chlorophyll a-WSCP, respectively. The action spectrum is broader and blue-shifted compared to the fluorescent lower exciton state. This finding can be explained by a slow protein relaxation between energetically inequivalent conformational substates within the lowest exciton state in agreement with the results of Schmitt et al. (J. Phys. Chem. B2008, 112, 13951).

Optical Properties and Persistent Spectral Hole Burning of Near Infrared-Absorbing Hollow Gold Nanospheres

We report on the characteristics and mechanism of persistent spectral hole burning of hollow gold nanospheres (HGNs) with near IR (NIR) surface plasmon resonance (SPR) absorption induced by femtosecond (fs) laser pulses. The HGNs were exposed to pulsed laser light at 810 nm, on resonance with their absorption band, at various laser powers while the total photon flux incident on the samples was kept constant. Depletion of HGNs responsible for 830 nm absorption was observed while simultaneous growth of bluer-absorbing HGNs, solid gold nanoparticles (AuNPs), or a mixture thereof was observed. This occurred only with fs pulsed laser irradiation and did not occur with continuous wave (CW) laser irradiation. Based on combined UV−vis spectroscopy and transmission electron microscopy data, the mechanism behind the persistent hole burning with fs laser irradiation is proposed to involve two possible processes: (i) conversion of NIR-absorbing HGNs to bluer-absorbing HGNs, and (ii) breakdown of NIR-absorbing HGNs into solid AuNPs directly. The branching ratio between these two processes depends on the peak power of the fs laser pulses with higher peak power favoring the second process. This hole-burning study is useful for understanding and exploring the potential use of HGNs in drug delivery with a laser as a trigger for release. In conjunction, theoretical calculations have been carried out to gain further insight into the optical absorption of HGNs, especially in terms of how the extinction coefficient depends on the structure of the HGNs in comparison to solid AuNPs. One interesting finding is that HGNs with thicker shells not only absorb at bluer wavelengths, but also have lower absorption as well as extinction coefficient. An HGN with the same outer diameter as a solid AuNP has a substantially larger extinction coefficient. These theoretical findings are supported by experimental results. The enhanced extinction coefficient is advantageous for applications such as photothermal ablation therapy (PTA) for cancer treatment. The dependence of the absorption coefficients on the HGN structure is also important for interpreting the hole-burning results that rely on changes in spectral position as well as intensity.

Persistent Spectral Hole-Burning in Diffuse Reflection: Application to Nanocrystalline LiGa5O8:Co2+

Persistent spectral hole-burning of an electronic transition measured in diffuse reflection is reported for the first time. The technique is applied to the electronic origin of the 4A2(F)→4T1(P) tr...

On the assignment of PSHB in D1/D2/ cytb559 reaction centers

We re-visit the phenomenon of persistent spectral hole-burning (PSHB) in isolated PS II reaction centers in light of advances in the understanding of the overall electronic structure of PS II. A recent analysis of non-selective photochemical hole-burning and the consequent changes in CD spectra associated with the photo-reduction of PheoD1 (the primary electron acceptor) supports an analysis in which very substantial and non-correlated chlorin site-energy inhomogeneity leads to a range of realizations of the exciton structure of reaction centers. The lowest energy excited state can be described as predominantly involving the dominantly ChlD1 (the primary acceptor) exciton, but in a significant fraction of centers the lowest excited state is a dominantly PheoD2 (the inactive pheophytin) exciton. The narrow linewidth of PSHB reported a decade ago in these systems, with homogeneous holewidths approaching that corresponding to the radiative lifetime, along with our ability to reproduce the published PSHB action spectrum, leads to the suggestion that aspects of hole-burning in these systems can be attributed to centers in which the exciton realizations lead to a predominantly PheoD2 character as the lowest energy exciton. This assignment is discussed in terms of models of the PS II reaction center.

The assignment of Qy(1,0) vibrational structure and Qx for chlorophyll a

We used non-photochemical persistent spectral hole-burning at 1.4 K to investigate the Qy(1,0) vibrational structure of Chl a in a water-soluble chlorophyll-binding protein (WSCP) which exhibits resolved structure in its broadband optical spectra. FranckCondon vibrational overlap factors were determined from the vibrational hole-burning data and used to simulate the Qy(1,0) spectra. The simulations were not able to accurately reproduce the details of the Qy(1,0) spectrum. This indicates a breakdown of the approximations used for the analysis and demonstrates that vibrationally induced mixing of electronic states (vibronic coupling) is active for Chl a. By considering the inhomogeneous broadening and vibrational hole-burning phenomena in the Qx and Qy(1,0) region of Chl-WSCP in addition to magnetic circular dichroism data, we favor the traditional placement of Qx at λ∼570–590 nm rather than the alternate assignment underneath the Qy(1,0) absorption near λ∼615–630 nm.

Slow light using spectral hole burning in aTm3+-doped yttrium-aluminum-garnet crystal

We report on light slowing down in a rare-earth-metal-ion-doped crystal by persistent spectral hole burning. The absence of motion of the active ions, the large inhomogeneous broadening, the small homogeneous width, and the long lifetime of the hyperfine shelving states make this material convenient for the burning of narrow persistent spectral holes. Since the hole can be burnt long before the arrival of the input signal, there is no need for a strong-coupling field, illuminating the sample simultaneously with the input signal, in contrast with procedures such as electromagnetically induced transparency or coherent population oscillations. Analyzing the slowing down process, we point out the role played by the off-resonant atom. Most of the incoming information is carried over to off-resonant atoms, while the pulse is confined within the sample. The observed speed-of-light reduction factor exceeds ${10}^{5}$.