Abstract
As environmental conditions and component degradation and failure are known to affect the performance of ultrafast lasers, it is important to monitor their state in any nonlinear optical study. This may be achieved by measuring the temporal width of the laser pulses using an autocorrelator. In this work, an autocorrelator for measuring the pulsewidth of mode-locked lasers was custom-built using pieces of equipment usually found in a typical ultrafast optics laboratory. The assembled equipment was tested using SESAM (Saturable Semiconductor Absorber Mirror) mode-locked neodymium-doped vanadate (Nd:YVO4) laser having manufacturer specified average output power of 1.6 W and 10 ps pulsewidth. Using the background-free autocorrelation technique, the pulse width of the laser was measured to be 10.4 ps. This type of autocorrelator is cost effective and may be handy in situations where research funds are limited; a scenario commonly experienced in research laboratories of developing countries. Additionally, the processes involved in assembling the autocorrelator provide a useful learning experience for new researchers. The study also outlined the processes involved in modifying an existing autocorrelation setup in order to measure laser beam spot size; a useful parameter in nonlinear optical studies.
Highlights
Since their invention in 1960 (Maiman, 1960), lasers have been employed in diverse fields such as medicine (Vij & Mahesh, 2013), optical communication (Marell et al, 2011), optical metrology (Silver et al, 2007), military (Anderberg & Wolbarsht, 2013) among others
As the nonlinear optical techniques for laser pulse width measurements do not provide a direct display of the pulse shape but instead give measurements of the correlation functions, the second-order autocorrelation function of the intensity I (t ) is expressed as (Ippen & Shank, 1997):
This is the function obtained through second-harmonic generation (SHG) in the KTP crystal since the SHG intensity I (2ω) is proportional to the product of the intensities of the two fundamental pulses
Summary
Since their invention in 1960 (Maiman, 1960), lasers have been employed in diverse fields such as medicine (Vij & Mahesh, 2013), optical communication (Marell et al, 2011), optical metrology (Silver et al, 2007), military (Anderberg & Wolbarsht, 2013) among others. Commercial autocorrelators are currently available on the market, they are beyond the reach of many research laboratories especially ultrafast laser users in the developing countries. In this case, custom-built autocorrelators may be preferable. The most versatile of these approaches is the knife-edge method (Cannon, Gardner, & Cohen, 1980; de Araújo, Silva, de Lima, Pereira, & de Oliveira, 2009) This is a beam profiling technique that allows for quick, inexpensive, and accurate determination of beam parameters with the possibility to adapt it for a wide range of wavelengths and high power beams. This work will highlight the steps involved in adapting an existing autocorrelation setup to measure the spot size of a laser beam
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