Random noise can help to improve synchronization of excimer laser pulses

Róbert Mingesz,János Mellár,Zoltán Gingl,Angéla Barna

doi:10.1098/rsos.150548

Abstract

Recently, we have reported on a compact microcontroller-based unit developed to accurately synchronize excimer laser pulses (Mingesz et al. 2012 Fluct. Noise Lett. 11, 1240007 (doi:10.1142/S021947751240007X)). We have shown that dithering based on random jitter noise plus pseudorandom numbers can be used in the digital control system to radically reduce the long-term drift of the laser pulse from the trigger and to improve the accuracy of the synchronization. In this update paper, we present our new experimental results obtained by the use of the delay-controller unit to tune the timing of a KrF excimer laser as an addition to our previous numerical simulation results. The hardware was interfaced to the laser using optical signal paths in order to reduce sensitivity to electromagnetic interference and the control algorithm tested by simulations was applied in the experiments. We have found that the system is able to reduce the delay uncertainty very close to the theoretical limit and performs well in real applications. The simple, compact and flexible system is universal enough to also be used in various multidisciplinary applications.

Highlights

Precise synchronization of events in time is essential in many experiments when time-dependent behaviour is monitored
The time resolution of the unit is limited to 10 ns, we could improve the timing accuracy well below this by using the jitter noise of the laser and additional random dithering
20 40 60 80 100 120 140 shot desired delay measured delay cables, optical receivers (HFBR 2521) and transmitters (HFBR 1521). These elements introduce excessive jitter; first we evaluated the performance without the use of the KrF excimer laser

Summary

Introduction

Precise synchronization of events in time is essential in many experiments when time-dependent behaviour is monitored. Excimer laser operation itself may need synchronizing units to control X-ray pre-ionization and master. The hydrogen thyratron used in excimer lasers to activate the high-voltage discharge has a certain switching time (so-called anode delay) which is subjected to a long-term drift caused by temperature changes. A random jitter is present in laser systems due to the gas discharge uncertainty. The proper control of the delay needs precise time measurement and tuneable delay units [6,7]. We have developed a universal, simple microcontroller-based delay-controller unit that features flexible software control and precise time-synchronizing hardware components [7]. The time resolution of the unit is limited to 10 ns, we could improve the timing accuracy well below this by using the jitter noise of the laser and additional random dithering. The system’s performance was tested by numerical simulations only; here we report on our experimental results of a laser pulse synchronization application in a KrF excimer laser

Experimental set-up and delay-controller operation

Experimental results

Conclusion