Photon-echo Relaxation Research Articles

Vibronic modulation of lineshapes in two-dimensional electronic spectra

We report and analyze oscillatory behavior of lineshapes in two-dimensional photon-echo relaxation spectra of a perylene-based dye molecule, whose four-wave-mixing signals are strongly modulated by coupling to low-frequency vibrational modes. Vibrational wavepacket motion is found to induce a pronounced beating of the anti-diagonal absorptive peak width, accompanied by orientational changes in the dispersive signal part. The effects are reproduced well by simulations based on a Brownian oscillator model, and can be assigned to periodic alternations in the relative amplitudes of rephasing and non-rephasing contributions to the spectrum.

Accumulated photon-echo spectroscopy for stained tissue samples

We performed phase relaxation-time measurements of the accumulated photon echo for normal and cancerous tissue samples of human liver, that were stained with several kinds of dye. Each dye interacted selectively with a specific kind of biomolecule in the tissues, for example, DNA, proteins, or lipids. The cancerous tissues showed a tendency to have shorter relaxation times than the normal tissues had. The difference of relaxation time observed between the normal and the cancerous tissues depended on the dyes that were used for staining, and the difference became most clear when the tissues were stained with a cyanine dye derivative, i.e., YO-PRO3 Iodide, which has a high selectivity for DNA. We performed the relaxation-time mapping of the accumulated photon echo (photon-echo imaging) for a liver tissue sample stained by YO-PRO3 Iodide. The photon-echo imaging was successful in showing a region of a highly differentiated hepatocellular carcinoma in the tissue sample, while fluorescence-intensity mapping could not identify the cancerous region in the same tissue sample. These results indicated a possibility that the reduction of accumulated photon-echo relaxation time observed in the cancerous tissues was caused by a change of microscopic dynamics of DNA.

New channels of photon echo relaxation in Y2SiO5:Pr3+ and LaF3:Pr3+ crystals

Experimental results on the investigation of low-temperature optical absorption spectra and temperature dependence of the photon echo (PE) amplitude signal in Y2SiO5:Pr3+ and LaF3:Pr3+ crystals at the transition H43(0)−3P0 of the Pr3+ ion are presented. It is shown that additional relaxation channels exist for PE in addition to the known phonon mechanisms. This is associated in a LaF3:Pr3+ crystal with the temperature variation of dipole moment at the Pr3+ ion transition. In a Y2SiO5:Pr3+ crystal, this is due to the thermally activated transitions for the Pr3+ ion between nonequivalent positions in the crystal lattice.

Accumulated photon-echo imaging for tissue samples

Microscopic mapping of accumulated photon-echo relaxation time, known as accumulated photon-echo imaging, has been developed as a new technique accessible to histological diagnosis. Photon-echo imaging for Rhodamine-stained tissue samples of human liver has been demonstrated by means of fluorescence detection of accumulated photon echo. In a liver tissue that included a moderately differentiated hepatocellular carcinoma, we obtained an accumulated photon-echo image that correlated with the histological diagnosis. However, for a liver tissue with a highly differentiated hepatocellular carcinoma, photon-echo imaging could not discriminate the carcinoma from a noncancerous liver tissue.

Intensity-dependent photon-echo relaxation in rare-earth-doped crystals.

Photon-echo-relaxation measurements made on the 3H4-3P0 transition of 0.01 at. % Pr3+:YAG (where YAG represents yttrium aluminum garnet), 3H4-1D2 transition in 0.1 at. % Pr3+:YAlO3, and 7F0-5D0 transition in 0.25 at. % Eu3+:YAlO3 show that the photon-echo relaxation rate increases when the intensities of the excitation pulses are increased. Although a part of the relaxation-rate increase in Pr3+:YAG may be attributed to an instantaneous spectral diffusion (ISD) in which the presence of excited neighboring Pr3+ ions change the local field and the absorption frequency of the rare-earth ions, our data deviate significantly from the ISD-model predictions. An additional intensity-dependent relaxation mechanism is required to explain the results.

Photon echo relaxation and hole burning in Tb 3+: LiYF 4 and LiTbF 4

Possible Anderson localization has been observed in LiTbF 4. Spin diffusion, field-dependent echo modulation, hyperfine population hole burning, and long-lived stimulated echoes have been studied in the dilute crystal.

Photon echo relaxation and hole burning in Tb 3+:LiYF 4 and LiTbF 4

Photon echo measurements on the lowest 7F 6 to 5D 4 transition in LiTbF 4 and 1% Tb 3+:LiYF 4 are reported. The dephasing rate exhibits a significant dependence on magnetic field, concentration, laser intensity, and temperature. Possible Anderson localization has been observed in LiTbF 4, and field-dependent echo modulation, hyperfine population hole burning, and long-lived stimulated echoes have been studied in the dilute crystal.

Photon echo relaxation in caesium perturbed by noble gases

The collisional relaxation of photon echoes generated on the 6S built1 2 - 7P built3 2 (455 nm) transition in caesium has been observed and measured as a function of perturber pressure. Values for the collision cross-sections have been obtained using helium, neon, argon and krypton as perturbers. There is good agreement between these results and those obtained from high resolution measurements of pressure-broadened line profiles. The echoes were observed using the polarization rotation technique and all the measurements were made at perturber pressures below 0.5 torr.

Photon-echo studies of collisional relaxation in weakly ionized noble-gas mixtures

Photon-echo relaxation rates are measured in weakly ionized plasmas of binary mixtures of noble gases, in which the photon echo generated on a transition in one noble-gas species is damped primarily by atoms of the second species. The special cases of pure krypton and xenon are extensions of previous work in pure helium, neon, and argon. With the exception of mixtures with helium as the perturber, measured relaxation rates are consistent with collisional line-broadening calculations.

Observation of Collisional Velocity Changes Associated with Atoms in a Superposition of Dissimilar Electronic States

Photon-echo measurements in atomic Na perturbed by He provide the first demonstration of the contribution of velocity-changing-like effects to the transverse relaxation of atoms in superposition of two states even when the states follow different post-collision trajectories. The apparent anomaly that broadening cross sections derived from either absorption line widths or photon-echo relaxation measurements are smaller than the total cross section for scattering of atoms in either pure state is explained.

Photon echo relaxation in LaF 3:Pr 3+

We have observed deeply modulated photon echoes from Pr 3+ ions in LaF 3 reflecting nuclear hyperfine interactions in both the ground 3H 4 and excited 3P 0 states. We infer splittings of 0.75 MHz for the 3P 0 state. Inhomogeneous broadening of the terminal levels is found to lead to echo modulation damping. A surprising concentration dependence of the photon echo relaxation rate is observed as well as a dramatically long-lived (3 min) stimulated photon echo.

Hahn- and stimulated photon-echo decay measurements in the lowest doublet-doublet electronic transition of triphenylmethyl in triphenylamine

The results of Hahn (two-pulse) and stimulated (three-pulse) photon-echo decay measurements in the lowest 2A ← 2A electronic transition of triphenylmethyl in triphenylamine are reported and discussed. From the Zeeman effect on the photon-echo relaxation behaviour we conclude that hyperfine and superhyperfine interactions play a dominant role in the optical (phase) relaxation process.

Photon-echo relaxation measurements with two dye-lasers application to pentacene- h14 and - d14 in p-terphenyl- h crystals at 1.5 K

Electronically controlled photon-echo relaxation measurements, using two nitrogen pumped dye-lasers, are reported for mixed crystals of pentacene- h 14 and - d 14 in p-terphenyl- h 14 at 1.5 K. In dilute mixed crystals (ca. 10 −8 M) the photon-echo lifetime is found to be exclusively determined by the fluorescence lifetime. Homogeneous linewidths of 7.1 and 5.9 MHz at 1.5 K are then calculated for the electronic origin of the 1B 2u ← 1A 1g transition of pentacene- h 14 and - d 14 respectively. The decrease in photon-echo lifetime at higher guest concentrations (ca. 10 −7 M) is ascribed to energy transfer between excited and neutral guest molecules.

Optical-phase relaxation at low temperature in the lowest 1B2u ← 1A1g transition of tetracene and pentacene in p-terphenyl

Temperature dependent optical absorption experiments on the lowest 1B1u ← 1A1g transition of tetracene in a p-terphenyl mixed crystal show that the loss of optical coherence is due to photon emission of the excited state and phonon scattering of the ground state. The resonant phonon that induces the optical phase relaxation process is shown to be of u-symmetry and its lifetime is obtained fromthe previously reported photon-echo relaxation results. For pentacene in p-terphenyl it is concluded that phonon scattering in both the ground and excited state contributes to optical phase relaxation.

Photon-echo relaxation in molecular mixed crystals

The results of a photon-echo relaxation study on the lowest 1B 2u ← 1A 1g transition of tetracene and pentacene in a p-terphenyl host crystal are reported. The photon-echo decay times were measured at 1.37 K and found to be 8.2 ± ns for tetracene and 13.8 ± 0.5 ns for pentacene. These relaxation times correspond to homogeneous linewidths of 19.4 and 11.5 MHz respectively and are over a factor of 10 3 smaller than the observed inhomogeneous linewidths in the optical absorption spectrum. Temperature dependent photon-echo intensity measurements further show that, below 3.5 K, optical relaxation is due to an orbach process with a presumably pseudolocalized phonon state. The resonant phonon frequency was measured to be 8.1 ± 1 cm −1 for tetracene and 21.2 ± 0.5 cm −1 for pentacene.

Magnetic field- and concentration-dependent photon echo relaxation in ruby with simple exponential decay

Magnetic field- and concentration-dependent, simple exponential photon echo decay in ruby is observed in apparent disagreement with previous work. Similar results are obtained with electron spin echoes.

Modulation and fast decay of photon-echos in ruby

Observations are reported on concentration effects, Cr-Al modulation and fast decay in photon-echo relaxation measurements in ruby, performed by the direct echo-signal versus time method.