W. Sibbett

Linear picosecond electron-optical chronoscopy at a repetition rate of 140 MHz

Abstract A picosecond streak camera operating in synchronism with C.W. mode-locked lasers provides real-time integrated measurement of repetitive luminous phenomena with a temporal resolution of ∼ 10 ps. The durations of pulses from an actively mode-locked argon ion laser (514.5 nm) have been measured to be ∼ 90 ps and the system is particularly suitable for the measurement of dye fluorescence lifetimes.

Thermal effects in phase-conjugation in saturable absorbers with picosecond pulses

Abstract Phase conjugation reflection with efficiencies of 400% for microsecond pulses and ∼50% for picosecond pulses has been obtained in saturable absorber dye solutions. The effect of different solvents on the generation of the thermal phase grating involved was investigated.

Picosecond phase-conjugate reflection from organic dye saturable absorbers

Abstract Phase conjugation with conversion efficiences of up to 50% has been obtained in DODCI and other saturable absorbers with picosecond pulses from a mode-locked dye laser. Reflectivity shows a quadratic dependence on pump intensity up to ~500 MW cm -2 .

Intensity dependent time‐resolution and dynamic range of Photochron picosecond streak‐cameras

The dynamic range of operation of Photochron I and Photochron II picosecond streak cameras is shown to depend upon the time-resolution employed. For events approximately 2 ps a useful dynamic range of 30 is obtainable, and this increases to a value of 180 for 30-ps events. No accumulative saturation effects occur at a time resolution as short as 2 ps.

Theoretical analysis of space‐charge effects in photochron streak cameras

The influence of space‐charge effects on the nature and extent of intensity‐dependent temporal broadening in picosecond and subpicosecond streak images has been investigated analytically. The results indicate that the limitations on the dynamic range of electron‐optical streak cameras result primarily from space‐charge effects which are most serious in regions of the streak tubes where the photoelectrons travel with low velocities for relatively long times. The predicted values of dynamic range have been found to be in reasonable agreement with experimental measurements for Photochron I and Photochron II streak cameras. Theoretical estimates of the dynamic range of the Photochron IV streak camera which is currently being developed have also been included.

Time resolved fluorescence of trans‐Stilbene in the picosecond regime

The Synchroscan streak camera system has been used to examine the temperature dependence of the fluorescence decay of trans‐Stilbene between ‐10 and 30 °C. Two components of the fluorescence have been detected; a short one varying between 125 and 64 psec over the range and a much weaker longer one varying from 690 to 1450 psec. The presence of the longer component may indicate a return to the transgeometry following initial photoisomerization.

Picosecond x-ray chronoscopy

Abstract An X-ray/VUV streak camera with a time resolution of ≈20 psec is described. X-ray pulses, from a laser plasma, down to 22 psec half width, separated by 42 psec, are clearly resolved. Photoelectron time-dispersion effects and the absolute sensitivity of the camera are discussed.

An experimental study of the primary parameters that determine the temporal compression of CW Nd:YAG laser pulses

Abstract An experimental study of temporally compressed CW Nd:YAG laser pulses using an optical fibre and diffraction grating pair technique has been carried out. The relevant experimental parameters have been varied so that a better insight into the physical processes could be gained and to enable some comparisons to be made with theory. Under optimum conditions an overall 47 × pulsewidth compression and 10 × enhancement in peak power have been achieved. Changes in fibre length, peak power and grating separation gave rise to outputs which showed good qualitative agreement with theoretical predictions.

Substituent and environmental effects on the picosecond lifetimes of the polymethine cyanine dyes

Using the synchronously operated streak camera, the fluorescence lifetimes of polymethines of the cyanine family have been examined under low power CW picosecond dye laser excitation. The effects of steric hindrance on the lifetimes and of atomic substitution within the dyes have been measured, with lifetimes ranging from 14 ps to ∼ 2 ns. The strong viscosity-dependent fluorescence lifetime exhibited by these dyes has also been investigated. In addition, deviation from a Single exponential decay was recorded for several of the dyes.

Characterisation of the output from a Q-switched/mode-locked cw Nd:YAG laser

Abstract Both single-shot and repetitively-operating streak cameras have been used for direct studies of the optical pulses produced by a simultaneously Q-switched and mode-locked cw Nd:YAG laser. Without prelase the mode-locked pulses are observed to be merely highly structured noise-bursts having durations of a few hundred picoseconds while with prelase, short (∼100 ps) stable pulses can be obtained at Q-switch repetition rates in excess of 1 kHz. These pulses are compared to those obtainable from the mode-locked laser without Q-switching.