Bleaching Of Ground State Absorption Research Articles

Sub-diffraction resolution pump-probe microscopy with shot-noise limited sensitivity using laser diodes.

We demonstrate the use of intensity-modulated laser diodes to implement pump-probe microscopy and achieved sub-diffraction resolution imaging with shot-noise limited sensitivity with a scheme of balanced detection. This technique has several applications for various types of induced transmission change, including excited-state absorption, ground state absorption bleaching and stimulated emission. By using our technique, biological imaging of mouse T cells and the axons of neurons in the cerebral cortex was demonstrated.

Joint Experimental and Theoretical Investigations of Two-State Mode Locking in a Strongly Chirped Reverse-Biased Monolithic Quantum Dot Laser

The influence of different biasing conditions of a passively mode-locked strongly chirped two-section quantum-dot laser on its ground state (GS) and excited state (ES) emission is investigated both experimentally and theoretically. Numerical simulations performed with a modified time-domain travelling-wave model are in qualitative agreement with experimental results and allow to identify the origin of the experimentally observed mode-locking regimes: the complex time-dependent coupling between the ES and GS absorption bleaching in the saturable absorber section. This coupling, together with the difference in group velocities of ES and GS pulses, is found to be responsible for low-frequency inter-modulation signatures as observed experimentally and verified in the simulations.

Radical Cation Generation from Singlet and Triplet Excited States of All-trans-Lycopene in Chloroform¶

On direct photoexcitation, subpicosecond time-resolved absorption spectroscopy revealed that the 1B(u)-type singlet excited state of all-trans-lycopene in chloroform was about seven times more efficient than all-trans-beta-carotene in generating the radical cation. The time constant of radical cation generation from the 1B(u)-type state was found to be approximately 0.14 ps, a value that was comparable for the two carotenoids. On anthracene-sensitized triplet excitation, radical cation generation was found to be much less efficient for lycopene than for beta-carotene. A slow rising phase (20-30 micros) in the bleaching of ground-state absorption was common for both lycopene and beta-carotene in chloroform and was ascribed to an efficient secondary reaction with a solvent radical leading to the formation of carotenoid radical cations. The reverse ordering in the tendency of the excited states of different multiplicities for the two carotenoids to generate radical cations is discussed in relation to the two carotenoids as scavengers of free radicals.

Radical cation generation from singlet and triplet excited states of all-trans-lycopene in chloroform.

On direct photoexcitation, subpicosecond time-resolved absorption spectroscopy revealed that the 1B(u)-type singlet excited state of all-trans-lycopene in chloroform was about seven times more efficient than all-trans-beta-carotene in generating the radical cation. The time constant of radical cation generation from the 1B(u)-type state was found to be approximately 0.14 ps, a value that was comparable for the two carotenoids. On anthracene-sensitized triplet excitation, radical cation generation was found to be much less efficient for lycopene than for beta-carotene. A slow rising phase (20-30 micros) in the bleaching of ground-state absorption was common for both lycopene and beta-carotene in chloroform and was ascribed to an efficient secondary reaction with a solvent radical leading to the formation of carotenoid radical cations. The reverse ordering in the tendency of the excited states of different multiplicities for the two carotenoids to generate radical cations is discussed in relation to the two carotenoids as scavengers of free radicals.

Excited state absorption in the gahnite glass ceramics and its parent glass doped with chromium

We report on comparison of the basic spectroscopy and first of all excited state absorption (ESA) characteristics measured for the chromium doped pink gahnite glass ceramics and its green parent glass doped with chromium. The ESA spectrum of the ceramics is rather predictable and reveals peaks which can be ascribed to doublet–doublet transitions, typical for the Cr 3+ ions in the high crystal field, and is additionally affected by the ground state absorption bleaching. Unlike the ceramics, the parent glass, being a low-field material, reveals quartet–quartet ESA, typical for the Cr 3+ ions in the low crystal field. The ESA spectrum apart of chromium-related features and bleaching of the chromium ground state absorption, is connected with other possible centers of the host. Based on basic spectroscopic data we create configuration coordinate diagrams for both cases, predict the shape of the expected ESA spectra and compare them with measured ones. A reasonable agreement has been achieved.

Laser flash photolysis study of ( E)-1-(2′-arylidene-1′-phenylhydrazinyl)-1,2-dibenzoylalkenes: Mechanistic aspects of photochemical ring closure

Several ( E)-1-(2′-arylidene-1′-phenylhydrazinyl)-1,2-dibenzoylethylenes, varying from one another in the nature of the p-substituent on the 2-benzylidene group, have been studied by nanosecond laser flash photolysis and pulse radiolysis. The transient absorption spectral changes from direct laser excitation (λ ex = 337.1 nm or λ ex = 355 nm) as well as under triplet sensitization by camphorquinone (λ ex = 485 nm) are explained in terms of the formation of zwitterionic intermediates in the course of intramolecular photocyclization (pentadienyl anion mode) and, in part by cis → trans isomerization about the ethylenic double bond. From the bleaching of ground state absorption, the lower limits for photochemical loss are estimated to be 0.01 – 0.1 (in benzene and in methanol). The triplets of the dibenzoylethylene substrates and the triplet excited states of zwitterionic intermediates are not observed on the nanosecond time scale, presumably because of their short-lived character.

Excited state absorption of 1,3,3,1′,3′,3′-hexamethylindotricarbocyanine Iodide: A quantitative study by ultrafast absorption spectroscopy

A quantitative investigation of HITC dissolved in methanol has been made using the method of ultrafast absorption spectroscopy with a streak camera. Samples were excited by picosecond pulses of a mode-locked ruby laser. Analysis of time-resolved spectra yielded non-exponential decay kinetics consisting of a fast (τ variable) and a slow (τ=1.13±0.08 ns) component. The excited state absorption spectrum has its maximum at 493 nm and shoulders at 415 and 540 nm. The excited state absorption cross section was determined by simulataneous measurement of the bleaching of ground state absorption taking polarization of excitation and probe light and excited state absorption at the laser wavelength into account. A value of σ1 (493 nm)=1.0·10−16 cm2 was found.