HfO2 thin films are widely used in laser system because of its superior optical and mechanical properties, especially high laser induced damage threshold. In this paper, single-layer HfO2 thin films were prepared by APS plasma assisted electron beam evaporation deposition. The effects of oxygen charging of electron gun, baking temperature, discharge current of APS source and bias voltage of APS source on optical properties, surface roughness, standing wave electric filed and laser induced damage threshold of HfO2 thin films were studied by orthogonal experiment. Experiment and analysis results showed that the characteristics of HfO2 thin films are closely related to the oxygen charging of electron gun, baking temperature and APS assisted processing parameters. Especially, baking temperature, oxygen charging of electron gun and bias voltage of APS source have great influence on laser induced damage threshold. Through the analysis of experimental date, the optimal combination of process parameters for APS assisted electron beam evaporation of HfO2 optical films were obtained.
Four types of lateral photoconductive semiconductor switches (PCSS) made of different materials are compared. The
PCSS made of GaAs, InP and Si are triggered by laser pulse to find out the effect on the voltage transmission efficiency.
The peak voltage transmission efficiency of GaAs PCSS is 93% at the biased voltage 1500V with the laser energy 1mJ.
On the same condition, the InP switch is only 63.63%. The Si switch can only acquire the efficiency 0.02%. The
difference of different materials employed for PCSS is analysed. The SiC PCSS is compared with the GaAs PCSS in the
relationship of the optical energy and the conduction resistance to analysed the voltage transmission efficiency in
theoretics. The university of Missouri-Columbia has done some research on the SiC PCSS, some of their experiment
results are reported.
High power sub-nanosecond electrical pulse system based on photoconductive semiconductor switch (PCSS) is reported.
To get high power sub-nanosecond electrical pulse, experiments of three kinds of switches such as a lateral
semi-insulating GaAs PCSS, gas gap added into the two electrodes of the switch on the GaAs chip and combinatorial
switchs of GaAs PCSS with gas switch are triggered by nano-second laser pulse. The source of the triggered laser is
YAG lasers, and the width of the laser is about 3.5 ns. A maximum current is only 38A by a single 3.5mm PCSS. The
combinatorial switch of a 3mm-gap PCSS and a 0.6~0.8mm gas switch is triggered at the biased voltage 4000V, a high
current pulse is acquired with the peak value above 5160A, and ns risetime. The voltage transmission efficiency is more
than 100% (129%), which can not be answered for the ohm-theorem. This phenomena is explained with the theorem of
plasma.
The experiments of ultra-wide-band electromagnetic radiation from Photoconductive Semiconductor Switches
(PCSS's) triggered by high repeating frequency YAG ps laser pulse are reported. Based on the experimental results of
GaAs PCSS's and InP PCSS's in the linear mode, it is indicated that the rise time of ultra-fast electric pulse generated by
PCSS's depends on the rise time and the width of the triggering laser pulse. The fall time of the electric pulse is mainly
effected by the lifetime of the carriers. By analyzing the relationship between the time-domain characteristic and the
frequency-domain characteristic of the ultra-fast electric pulse generated by PCSS's, it is found that the frequency band
of electromagnetic radiation is mainly determined by the rise time and the fall time of the ultra-fast electric pulse. The
high-frequency component of frequency spectrum of electromagnetic radiation is determined by the rise time of electric
pulse, and the low-frequency component is determined by the fall time. The ultra-fast electric pulse whose rise time is
less than 100ps is obtained from GaAs PCSS's, and the ultra-fast electric pulse whose rise time is about 200ps is
obtained from InP PCSS's.
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