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Q Switched Resonant Cavity

IP.com Disclosure Number: IPCOM000035039D
Original Publication Date: 1989-May-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

May, P: AUTHOR

Abstract

A resonant transmission line cavity is defined by infinite impedance discontinuities (i.e., opens). One of the opens is formed by a switch (e.g., switching transistor or photoconductive switch). The cavity is driven photoconductively in resonance by a semiconductor laser at the appropriate resonance frequency. The open switch is driven at a submultiple of this frequency, thus changing the Q of the cavity and allowing an output at this switching frequency. A Q switching method of producing electrical pulses of magnitude at a submultiple of the semiconductor laser driving frequency for a linear transmission line resonant cavity is described. The photoconductive switch in the cavity is fast, damaged polysilicon, for instance, and is most easily formed by sliding contact (see the figure).

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Q Switched Resonant Cavity

A resonant transmission line cavity is defined by infinite impedance discontinuities (i.e., opens). One of the opens is formed by a switch (e.g., switching transistor or photoconductive switch). The cavity is driven photoconductively in resonance by a semiconductor laser at the appropriate resonance frequency. The open switch is driven at a submultiple of this frequency, thus changing the Q of the cavity and allowing an output at this switching frequency. A Q switching method of producing electrical pulses of magnitude at a submultiple of the semiconductor laser driving frequency for a linear transmission line resonant cavity is described. The photoconductive switch in the cavity is fast, damaged polysilicon, for instance, and is most easily formed by sliding contact (see the figure). The cavity defining switch should ideally recover within the transit time of the cavity (within 250 ps if 4 GHz is the resonant frequency of the cavity and consequently driving frequency of the semiconductor laser) if one pulse is to be picked out at the Q switching frequency. The switch could be another photoconductive gap but made from undamaged polysilicon (recombination time of order 200 ps) which would therefore be more efficient, for a given excitation power, at transfering charge. More convenient, however, would be an all electrical switch, such as a fast bipolar transistor (can certainly be faster than 4 GHz) with a sufficiently low on-resistance....