ABSTRACT
This chapter provides an update on the lasers in terms of their intensity, places where they are developed, and the related regimes where they best contribute. A special variety of laser (light) is required to detect the molecular level's activities because the molecules are very small and move fast. The solution to capture the motion at the molecular level is an ultrafast laser light, which is also called an attosecond laser. A detailed depiction of the attosecond laser is given in this chapter. Distinct methods to generate attosecond pulses in X-ray free-electron lasers (XFELs) such as methods based on energy and density modulation, use of multi-slotted foil for emittance spoil, and tilting electron beam inside an undulator are discussed. The imperative applications of attosecond XFEL pulses are also given. Finally, an alternate improved X-ray source is introduced, which is also known as γ-ray light source.
