A. Andreoni

Matching of group velocities in three-wave parametric interaction with femtosecond pulses and application to traveling-wave generators

The use of suitable noncollinear phase-matching configurations in type-I (e–oo) parametric interaction greatly improves the group-velocity matching among pump, signal, and idler pulses. A numerical model, well supported by the experiments, shows that the compensation of group-velocity mismatch can be achieved over the entire tuning range for pulses as short as few tens of femtoseconds. A general feature of the noncollinear interaction, the front tilt of the generated pulses, is experimentally investigated for a LiIO3 traveling-wave generator. A novel β-barium borate traveling-wave parametric converter pumped with 130-fs blue pulses from a frequency-doubled amplified Ti:sapphire system provides broad tunability in the visible with pulse durations as low as 90 fs and with a single-pass conversion efficiency as large as 40%.

LASER PHOTOSENSITIZATION OF CELLS BY HYPERICIN

Abstract— Administering a light dose of 90 J/cm2 at 599 nm during incubation with hypericin to a highly differentiated normal epithelial cell line(FRTL–5), derived from Fisher rat thyroid, and to a neoplastic cell line(MPTK–6), derived from the lung metastases of a thyroid carcinoma induced in Fisher rats, produces cell kill at drug doses 1000 times lower than those necessary to cause the same mortality in the dark. The photocytocidal activity of this polycyclic quinone drug on neoplastic cells is superior to that of antitumor anthraquinone drugs, such as daunomycin and mitoxanthrone, and to the photosensitized antiviral activity previously reported for hypericin.

Matching of group velocities by spatial walk-off in collinear three-wave interaction with tilted pulses

We demonstrate that, for tilted pulses, the contribution to group velocity that is due to spatial walk-off can compensate for the group-velocity mismatch in three-wave interactions. With 100-fs, 0.4-Zmicrom pump pulses in beta-barium borate, we obtained efficient parametric generation of collinear superfluorescence tunable in the range from 0.456 to 3.25 microm.

Visible pulses of 100 fs and 100 μJ from an upconverted parametric generator.

Upconversion by sum-frequency and second-harmonic generation of pulses from a Ti:sapphire-pumped parametric generator provides 50-120 μJ, sub-100 fs, bandwidth-limited pulses at 470-700 nm.

Efficient conversion of femtosecond blue pulses by travelling-wave parametric generation in non-collinear phase matching

Abstract The matching of group velocities achieved in non-collinear three-wave interaction is shown to yield efficient parametric conversion of femtosecond pulses from a frequency-doubled amplified Ti:sapphire laser. Tunability in the whole visible range, pulse duration of 90 fs and single-pass energy conversion efficiencies as large as 40% have been obtained in b-BaB 2 O 4 .

DYNAMICS OF ANTHRACYCLINES/DNA INTERACTION: A LASER TIME‐RESOLVED FLUORESCENCE STUDY*

Abstract— The dynamic interaction with DNA of two representative anthracyclines, daunomycin and 5‐iminodaunomycin, differing in the redox properties, DNA affinity and cardiotoxicity, has been characterized by laser time‐resolved fluorescence decay. The free drug fluorescence decay is mono‐exponential for daunomycin in both phosphate and TRIS buffer and becomes biexponential in the case of 5‐iminodaunomycin when the phosphate buffer is used. In the presence of DNA, daunomycin excited with a mode‐locked Ar laser at 364 nm shows a three‐exponential fluorescence decay with time constants T1=2.92 ns, T2= 1.42 ns, T3=0.31 ns. The first lifetime refers to the decay of the excited state of the chromophore bound on the DNA backbone, whereas T2 and T3 are assigned to two different conformations of the intercalation complex. An estimate of the molar extinction coefficient and the relative quantum yield of the variously bound drug is made. The 5‐iminodaunomycin fluorescence decay lifetime is less sensitive to the nature of the environment probably because, being a poorer intercalator, it binds more easily on the phosphate backbone and thus the electronic perturbation resulting from the binding is not as strong as in the case of daunomycin.

Two-step photoactivation of hematoporphyrin by excimer-pumped dye-laser pulses

The selective excitation of high lying singlet or triplet states of hematoporphyrin has been achieved using high peak-power nanosecond pulses generated by excimer-pumped dye lasers. The interaction involves two steps: a pulse at 630 nm raises the molecules to the S1 state and a second one, at 481 nm, further excites them either to a higher singlet state if shed simultaneously or to a triplet state higher in energy than T1 if it arrives delayed with respect to the pulse at 630 nm by a time interval longer than the S1 lifetime. Photodegradation of L-tryptophan (100 microM in 30vol.%methanol-70vol.% buffer, pH 7.4) sensitized by 21 microM hematoporphyrin is reported. While a pure type-II mechanism, which obeys the time-intensity reciprocity law up to peak-intensity values of about 20 MW cm-2, is photosensitized by pulses at 630 nm, strong non-linearities are found for pulsed irradiation at both 630 nm and 481 nm, i.e. when the sensitizer is pumped to high lying singlet states and when it is pumped to high lying triplet states. The dependence of the subsequent reactions on the presence of oxygen and their competition with the photodynamic action has been investigated; in particular, a pathway was observed in which an electron was photoejected from a hematoporphyrin high energy triplet, showing maximum efficiency when the pulses were delayed by 16.4 ns.

A collinearly phase-matched parametric generator/amplifier of visible femtosecond pulses

We report on the generation and amplification of ultrashort pulses of /spl ap/1.5-/spl mu/J energy, tunable in the visible down to 456 nm, through travelling-wave parametric interaction in a single /spl beta/-BaBO/sub 4/ crystal, operated in type-I phase matching and collinearly pumped by frequency-doubled Ti:sapphire pulses with the fronts suitably tilted to match the group velocities.

TIME‐RESOLVED LUMINESCENCE SPECTROSCOPY OF PHOTOSENSITIZERS OF BIOMEDICAL INTEREST*

Studying the fluorescence decay of chromophores, either used as fluorescent labels to stain specific biomolecules or as photosensitizers to produce irreversible chemical or physicochemical modifications on biological substrates, is being demonstrated to be a valuable method of investigating the interactions underlying a variety of phenomena. In fact, all possible primary steps in a photosensitized biological system are phenomena that may occur during the chromophore S, lifetime and act as quenching mechanisms of the S, state. Thus they can be identified, and the relative importance of the corresponding transient species quantitatively determined, with suitable techniques of time‐resolved fluorescence spectroscopy. The examples discussed in this paper concern both tumor photosensitizing drugs, such as anthracyclines and porphyrins, and skin sensitizers (e.g. furocoumarins).

Ultra-broadband and chirp-free frequency doubling in β-barium borate

A method is presented to render first- and second-order dispersion effects in second-harmonic generation in β-barium borate negligible in the bandwidth of 5 fs Ti:sapphire pulses.