Light activated semiconductor switches (LASS), when operated in the linear regime, have demonstrated the highest power and fastest rise-time of any other solid state switch. This, in conjunction with their picosecond jitter, allows their integration with electro-optic and magneto-optic devices to serve as an optically controlled optical switches (OCOS). The combination of OCOS with various other optical elements and gain media allows the assembly of various optical circuits that are faster, smaller in size and operate at a higher power density. This paper will discuss the underlying principles of such optical circuits. In addition, experimental results of a microlaser which is Q- switched with an LASS driven Pockets cell with a rise-time of 70 ps will be described, and future laser development based on LASS technology will be presented.
We report on the application of new electro-optic modulators which are controlled by photoconductive switches. Various configurations of modulator are presented and are applied to several applications. Experimental results are presented in which a photoconductively controlled modulator is used to Q-switch and cavity dump a Nd:YAG laser, utilizing only a single external trigger. The same modulator is also used to Q-switch, mode-lock and cavity dump the same laser. The use of the modulator results in a single laser being able to generate pulses in three duration ranges, i.e., approximately 20 ns, approximately 2 ns and approximately 70 ps. A similar modulator is used to suppress the pre-pulse generated by a regenerative amplifier and help attain a 105 contrast ratio between signal and pre-pulse. Other modulators and applications are presented, including an approximately 30 ps Pockels cell for use as an optical gate.
The use of linear photoconductive switches rather than nonlinear switches for the generation of Ultra-Wide-Band (UWB) pulses provides advantages such as jitter-free operation, low losses, and a reduction of the electrical and mechanical stresses in the switch. These advantages lead to the operation of many switches in series and/or parallel, higher average powers and longer lifetimes. Energy Compression Research Corporation (ECR) has demonstrated an advanced UWB source based on light activated silicon switches (LASS). The UWB source consists of a single LASS device mounted on a low impedance (< 0.5 (Omega) ) microstrip transmission line and a high fidelity impedance transformer connected to a 50 (Omega) coaxial connection. The voltage was measured at low impedance and 50 (Omega) to verify the efficiency and fidelity of the impedance transformer. After a transformation of 110:1 in impedance, the measurement at the end of the transformer verified that pulse rise-time was less than 100 ps and the overall efficiency was 50%. The system was tested up to 10 kV into 50 (Omega) before connector breakdown limited further increase. Larger powers can be radiated if the transformer is directly connected to the antenna.
We examine the limitations of light activated semiconductor switches from a pulsed power point of view particularly the power and the speed. The factors considered fall into three categories namely electromagnetic principles physical properties and carrier generation. We show how after a full examination of the switch in a real operating environment we are led to the choice of a silicon junction with linear activation as the optimum design for a repetitively switched high power device.
The light activated semiconductor switch is potentially the fastest most powerful switch available for pulse power and microwave generation applications. We will examine the requirements of the laser employed in activating this type of switch such as the optical energy required for activation and risetime. We will also present different configurations and compare them in terms of e. g. cavity complexity magnitude of optical prepulse and ability to suppress jitter.
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