R.P. Jones

Picosecond spectroscopy using a picosecond continuum

Abstract This paper describes the generation of a continuum which has a time duration equal to or less than the picosecond pulse which generates it. The spectrum of the continuum is several thousand wavenumbers in width. Experimental methods are presented which enable one for the first time to conduct absorption spectroscopy measurements in the picosecond scale. As an example of this method we describe the absorption and emission picosecond kinetics of a bleachable dye 3,3 diethyloxodicarbocyanine (DODC).

Time resolved picosecond emission spectroscopy of organic dye lasers

Abstract A technique is described for the direct measurement of radiationless relaxation in excited molecules by time-resolution of picosecond stimulated emission. Stimulated emission has been observed from unequilibrated vibronic levels of the first excited singlet state in fluid solution. In addition fine-structure has been detected in the stimulated emission.

Time‐Resolved Absorption Spectroscopy in the 10−12 ‐sec Range

A technique is described for a single‐shot time resolution of picosecond events. Some examples are given which demonstrate the feasibility of this method for making accurate measurements with a time resolution of ∼ 10−12 sec.

Observation of fluorescence originating from transitions between excited electronic states in a large molecule

In this note we report the observation of emission of the azulene molecule in the region of 13 200 cm−1, characterized by a quantum yield of 10−7, which is assigned to the 1A1(2) → 1B1(1) radiative transition between excited electronic states of a large molecule.

Photobleaching and recovery times of the mode-locking dye DODCI

Abstract Recovery times for the photobleaching of the saturable absorbing dye DODCI by picosecond pulse excitation are reported. Variations in DODCI concentration and exciting pulse power density result in recovery times ranging from ≈10 ps at high concentration/high power to >250 ps at low concentration/low power. These results not only corroborate out earlier data for fast recovery times in DODCI but also explain the inability of other investigations to confirm these findings.

Nonlinear aspects of relaxation in mode-locking dyes: DODCI

Abstract Relationships between photobleaching recovery times and excited state lifetimes for mode-locking dyes are treated. It is shown that under appropriate excitation conditions the recovery time may be substantially shorter than the lifetime of the excited state, in agreement with results which have been reported for DODCI. The existence of a two component decay is consistent with a self-dumping mechanism operative at high power densities. Proposed production of a DODCI photoisomer is examined with respect to nonlinear effects present during intense pulse excitation.

Relaxation of excess electrons in a polar solvent

Abstract We report the observation of the ultrafast relaxation of a quasifree electron to the localized excess electron state in water. Quasifree electrons were generated by photoionization of aqueous ferrocyanide solutions by the fourth harmonic of a mode locked Nd 3+ laser. The rate of formation of the localized hydrated electron is ≈ 2 psec.

Pīcosecond time resolution of stimulated Raman of alcohols, and their relationship to the generation of a picosecond continuum

Abstract The simultaneous time and frequency resolved spectra of stimulated Raman scattering (SRS) generated in D 2 O, H 2 O alcohols and diols by picosecond pulses are utilized to measure the vibrational relaxation of these liquids. The relationship between this SRS and the origin and spectral width of a broadband continuum is examined. It is shown that strong experimental evidence exists suggesting that in these liquids under a high power condition the SRS plays a major role in the existence and extent of the continuum.

Picosecond‐gated optical amplifier

A picosecond‐gated optical amplifier (PGOA) characterized by high gains (≳102), large extinction ratios (∼105), and short aperture times (∼10 psec) is described. The active component of the system is a saturable absorbing dye which is irradiated by a high‐intensity ultrashort laser pulse. The technique is illustrated by simultaneously gating and amplifying a weak picosecond continuum pulse propagating through a scattering medium. Performance characteristics of the PGOA and ultrafast shutters are compared.

Optical third harmonic generation in organic liquids

Abstract The efficiency for third harmonic conversion in pure organic liquids is found to be a factor of 100 larger than for fused silica. The liquids studied have large absorption cross sections which can be empirically related to the third harmonic conversion. The data suggest that high absorption cross sections increase the third harmonic conversion. The pure organic compounds studied indicate that this class of compounds can provide new and efficient media for harmonic generation.