HF amplifiers

Abstract

The performance of a cw HF chemical laser master oscillator with power amplifier was measured as a function of input power, oscillator/amplifier flow field match/mismatch and location of the optical axis of the input beam. The amplification ratio is an inverse function of the input power (intensity) and, for maximum amplification, the peak of the intensity distribution must be matched to the peak of the zero power gain distribution in the amplifier. The match/mismatch of the oscillator/amplifier flow fields has a second order effect on amplifier performance. The measured rout versus in performance curve showed that, after a continuous increase, the difference rout in remained almost constant over a wide range of input powers and that about one third of a device's oscillator output must be input to obtain amplifier output equal to the device's oscillator performance.When the input beam contained time-dependent oscillations, the amplitude modulation of the output beam was reduced by a factor that equaled the amplification ratio of the amplifier; the amplifier had no effect on the period (frequency) of the oscillations of the input beam. An amplifier performance model that predicts a device's amplifier performance given the device's oscillator performance as a function of reflectivity was developed. Excellent agreement between model predictions and experimental data was obtained.The model was used to predict multiple pass amplifier performance. The results showed that, with a two pass amplifier, one oscillator could drive six amplifiers. When the amplifier performance curves were plotted in terms of out versus where = PjjpfPosc, the curves for different devices collapse to one.For this study of amplifier performance, a Helios CL I laser or a Helios CL II laser was used as the oscillator while another Helios CL II laser was used as the amplifier. The CL II's are identical, two channel, arc driven, subsonic, cw HF chemical lasers. The flow channel of the CL I laser is identical to one of the flow channels of the CL II lasers. This permits the flow fields of the oscillator and amplifier to be identical when the CL I laser is run at one half the flow rates of the CL II laser. Section 2 summarizes the amplifier performance data. An analytical model to predict amplifier performance is introduced in Section 3. Section 4 contains an evaluation of amplifier scaling relations. Implications for MOPA performance are discussed. In Section 5 the amplifier performance model is extended to predict multipass amplifier performance. Several concluding remarks are given in Section 6.

Apoptosis Biochemical events and relevance to cancer chemotherapy

“…The finding that bci-2 provides a survival advantage for the cells [4043] by preventing the onset of apoptosis [44,45] suggests that, in some cells, programmed death may bc negatively modulated by other genes. hcl-2 has been shown to be involved in prevention of apoptosis in T cells [46], thymocytes [47], germinal center 6 ceils and Burkitt lymphoma cells [48], and in pre-B leukemia lines [49]. Recent evidence suggests that high levels of bcl-2 enhances cell survival under conditions of repressed c-rrt~+c expression, probably by mobilisation of Ca" from mitochondria to cytoplasm.…”