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Good laser focus is crucial for ultrafast measurements

In this research we study the focus quality of a laser beam containing ultrashort laser pulses. We show that different wavelength components of these pulses are focused at different positions. This affects both the pulse duration and the intensity. By comparing the quality of the focus for different generation geometries we conclude with which is the best for generating the short and intense pulses necessary for atomic filming. 

What are the electrons actually doing around the nucleus of an atom? That is a question we have to ask to fully understand matter, the basis of our universe. However, electrons are difficult to study due to their very fast dynamics. To be able to observe the behavior of the electrons, we need a camera that has a higher frame-rate than the speed of the electrons.

If we can understand the behavior of electrons in atoms, we can learn to control matter in a completely new way. This could lead to all kinds of applications that we don’t know of today. Just like the scientists first trying to understand electricity, we have no idea what new technology awaits us.

Since the early 2000s we’ve been able to study how atoms interact with light using extremely fast, attosecond laser pulses. These pulses are so short in time that you could fit 10 000 trillion of them in one second. However, there is a catch. To be able to use these short pulses, the laser beam, which they are traveling in, needs a nice focus where the pulses meet the atoms. If the focus is smeared out, the light intensity becomes lower and the pulse duration longer.

These laser pulses are built up by several wavelength-components. That means light of different colors are added up and together they form the light pulse. Characterizing the focus by using a simple knife-edge, we have found that the different wavelength-components of the pulses are actually focused at different positions. Their focus positions also depend on how we generate the pulses. 

Focusing Properties of High-Order Harmonics, Maria Hoflund, Ultrafast Science Journal