The focus of this research was on the testing and characterization of light emitting diodes (LEDs) when used as replacements for second harmonic crystals in optical autocorrelation measurements. A range of experiments were performed to determine the response of these devices under various operating conditions. The results of these experiments were found to be inconsistent with the majority of previous work, producing inaccurately wide pulse width measurements. The measurements also show signal shoulders which are separate from the autocorrelation peak. These shoulders extend over a very long range (several picoseconds), and have useful applications for finding the point of zero delay in experimental setups. Theoretical analysis supported by simulation was also performed to provide insight into the mechanism at work to produce these features. While further investigation is required, this research has produced two very useful results. The inaccuracy which has been discovered in the pulse width measurements has provided a cause for caution when using LEDs in autocorrelation systems. More importantly, a new application has been identified for these measurements, and this application is improved by the features that make autocorrelation measurement undesirable.