Passive negative feedback in mode-locked solid-state lasers.
Passive negative feedback by an intracavity GaAs platelet in actively/passively mode-locked solid-state lasers is reexamined, and the role of both single- and two-photon absorption in determining the features of the pulses and the pulse train is explored and compared with the experimental results. The time–bandwidth product is shown to acquire in the steady-state part of the train a value close to the minimum allowed by the uncertainty relation.
Theory of passive negative feedback in passively mode-locked Nd: Host lasers
Abstract The theory of pulse shortening and train stretching in passively mode-locked solid-state laser, controlled by a passive negative feedback, is presented for the case of an intra-cavity two-photon absorbing semiconductor feedback element. It is shown that it acts simultaneously as power limiter and pulse compressor, ensuring optimum operation of the intra-cavity saturable absorber, and generating very long and stable trains of energetic, almost bandwidth limited pulses.
VLA stereoscopy of solar active regions. 2: Altitude, relative motion, and center-to-limb darkening of 20 centimeter emission
A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of q(sub A) approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin(exp 2)B)). 5. We find a statistical limb darkening, which can be described by the relation (T(sub B)(alpha))/T(sub B)(0)) = 0.4 + ((0.6(cos(exp 2) alpha)) for sources with T(sub B) greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance.