Objective Laser time fiducial system is needed in high power laser facility for tracking synchronization change in experiment caused by disturbances such as collimation and device replacement. Traditional time fiducial is an electrical trigger pulse input to the AUX channel of oscilloscope which is convenient but has obvious jitter (about 150 ps). Moreover, the electrical trigger sensitive to the electromagnetic interference. Another time fiducial form is an infrared fiducial can transfer a long distance in fiber and been send to an independent channel of oscilloscope. Infrared fiducial has a good accuracy but employ a measurement channel. In this article, we propose a new time fiducial scheme based on optic-electric and electric-optic transformation for getting a blue time fiducial signal @450 nm which can use the vacuum photodiode detecting together with UV pulse. The scheme provides a rapid fiducial signal with long transmission ability for UV pulse synchronization monitor and has a monitoring precision as high as 10 ps.
Methods The study presents a fiducial system scheme based on optic-electric and electric-optic conversion. Firstly, arbitrarily waveform generator driven a M-Z modulator to modulate continuous infrared laser and infrared time fiducial signal been produced. Secondly, infrared time fiducial transferred a long distance by SM fiber and been converted to electrical signal by a photodiode. Thirdly, the electrical signal drive a direct-modulation LD and a blue time fiducial signal @450 nm is gotten. The final fiducial signal can be reach an index of 47 mW output power, 10% power jitter and 120 ps laser pulse width.
Results and Discussions According to the scheme, the monitor jitter caused by fiducial power jitter, fiber length variation follow with temperature, oscilloscope noise and photodiode noise have been tested and analyzed. According to the analysis, the scheme can get a monitor accuracy of 10 ps with a 24.5-25.5 ℃ temperature variation. An experiment for examine monitor accuracy is done with 24.8-25.2 ℃ temperature variation, the monitor accuracy gotten in experiment is 7.2 ps which is coincide with the theoretical analysis result (7.03 ps).
Conclusions In this study, a fiducial system scheme based on optic-electric and electric-optic conversion is proposed for high power laser facility synchronization monitor. In the scheme, infrared time fiducial signal firstly been transferred a long distance by SM fiber and been converted to electrical signal by a photodiode, after that the electrical signal drive a direct-modulation LD and a blue time fiducial signal @450 nm is gotten. The final fiducial signal can be reach an index of 47 mW output power, 10% power jitter and 120 ps laser pulse width. The experiment and theoretical analysis indicates that the method can providing a rapid fiducial signal with long transmission ability for UV pulse synchronization monitor, the monitoring precision can be as high as 10 ps.
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