J. N. Bradford

Effect of self-phase modulation on the evolution of picosecond pulses in a Nd:glass laser

Many authors have reported disparate characteristics of pulses from Nd:glass mode-locked lasers. From these it has become clear that the well-developed pulse has a frequency sweep or subpicosecond structure and yields a contrast ratio less than the ideal 3 in the two-photon-fluorescence measurement. On the other hand, the early pulse is well behaved, has simple temporal and spectral structure, and yields a contrast ratio of 3 in TPF. The measurements are almost all indirect. Theories explaining the early pulse have appeared, but these fail for the fully developed pulse.The authors present time-resolved spectrograms, covering pulse development from 1/50 peak intensity, where the pulse is well mode-locked, to full development, where spectral structure is complex. A numerical analysis, including self-phase modulation, non-linear absorption, amplification and dispersion, yields results that qualitatively agree very well with the experimental records, suggesting that self-phase modulation plays an important role in the evolution of mode-locked pulses in a Nd:glass laser.

Temporal and Spectral Development of Mode Locking in a Ring‐Cavity Nd:Glass Laser

Temporal and spectral development of mode locking was investigated in a ring‐cavity Nd : glass laser. It was found that whenever a mode‐locked pulse formed in the ring cavity a satellite pulse would develop traveling in the opposite direction. The varying delay of the satellite pulse permitted time‐resolved spectroscopy of the early stages of mode‐locked oscillation. It was found that the spectral distribution broadens from 3 to 80 A because of selfphase modulation inside the laser cavity.

A sensitive system for measuring atmospheric depolarization of light.

An improved instrument for measuring depolarization of linearity polarized light has been assembled and operated. It is a hundred times more sensitive than previous devices used for similar measurements, and it can detect depolarized light amounting to less than 10(-8) of the total transmitted light. This sensitivity is achieved by means of a high quality Wollaston prism and a differential detection scheme. Preliminary measurements over a 600-m path indicate that atmospheric depolarization is less than the detection limit of 10(-8).

Compensating for Pump-Induced Distortion in Glass Laser Rods

Since crystalline and glass laser materials of high optical quality became available, thermal distortion and other optical path length anomalies introduced by optical pumping have been the principal obstacles to diffraction-limited laser operation. Quelle published the first theoretical treatment of pump-induced thermal distortion. Subsequently, Riedel and Baldwin extended the theory to include refractive index changes due to the increased excited state population during pumping and applied Fermats principle to the calculation of ray paths. Several workers have made experimental observations of the pump-induced optical path length changes in both ruby and neodymium glass. In all instances, optically pumped neodymium glass rods were shown to behave as diverging lenses. Streak interferograms made by Welling and Bickart, however, show

Passive mode locking and picosecond pulse generation in Nd:lanthanum beryllate

The passive mode‐locking characteristics of Nd:lanthanum beryllate (Nd:BEL) have been studied for the two linearly polarized laser transitions at 1.070 and 1.079 μm. Streak‐camera measurements of pulse duration and spectral broadening in the pulse‐train emission show that Nd:BEL can generate minimum‐bandwidth pulses of ⩽15 psec, some 2–3 times shorter than for Nd:YAG.