The injection of an optical signal into a semiconductor laser biased near or above the lasing threshold modifies the coupling between the free carriers and the intracavity field. The detuning between the frequency of the injected signal and the free-running oscillation frequency and the ratio of the photon lifetime to the carrier lifetime are key parameters in determining the enhancement of the carrier-field resonant coupling frequency and the stability of the output field. Experimental results using a vertical cavity surface emitting laser biased near threshold are in agreement with calculations using a lumped-element oscillator model.
This article argues that the instructional scaffolding metaphor may be reconceived as distributed scaffolding when multiple means of influence are provided in a service-learning setting. In the service-learning course described here, the professor's role is largely as designer of activity settings for preservice teacher candidates, through which the students construct their own conceptions of teaching culturally diverse populations. The course involves a set of interrelated settings: a tutoring experience at the city's alternative high school; the reading of books from a menu of texts that cover a range of diversity topics; the discussion of these books in book club meetings independent of the professor's direct influence; and the whole-class discussion of these texts, led by each student book club. The distributed nature of the course scaffolding is illustrated with an excerpt from one book club's discussion.
The first experimental results on a confocal unstable resonator with 90 degrees beam rotation (UR90 or HiQ) are presented. A beam quality of 1.06 was observed, and it varied by a maximum of 0.08 over a resonator misalignment range of 1 mrad. The outcoupled beam's polarization was circular. Reverse mode suppression was achieved on UR90 with a suppressed vs unsuppressed ratio of 115:1. Measurable reverse mode suppression was obtained with as little as 2% of the full reverse mode strength. Most of these results are compared with those for a conventional ring resonator.
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