Fundamentals of Ultrafast Pulse Compression

The 1999 Nobel Prize in Chemistry for femtochemistry, the 2005 Nobel Prize in Physics for femtosecond-based optical frequency combs, the 2018 Nobel Prize in Physics for chirped pulse amplification (CPA), and the 2023 Nobel Prize in Physics for attosecond science driven by femtosecond pulses—four Nobel Prizes awarded over the past three decades in recognition of femtosecond laser science—have greatly inspired the "femtosecond community" worldwide.

An attosecond pulse is an ultrashort light pulse with a duration on the attosecond timescale (1 attosecond = 10⁻¹⁸ seconds). It is typically generated via high-order harmonic generation (HHG), a process in which an intense femtosecond laser pulse interacts with a medium (e.g., a gas), causing electrons to be transiently liberated from atoms or molecules and then rapidly recombine. During this recombination, photons of extremely high frequency are emitted, forming the attosecond pulse.

When it comes to attosecond science, one must mention the world's largest attosecond science facility—ELI-ALPS, located in Hungary. A detailed introduction to this facility was previously provided in Boliang Technology's official public account. We encourage readers to revisit the article: "Approaching Europe's Extreme Light Infrastructure: ELI Series (Part 4)." The femtosecond laser sources employed there offer a glimpse into the most advanced femtosecond laser technologies and leading companies in the field, including:

• Light Conversion (Lithuania) – OPCPA systems,

• Active Fiber Systems (Germany) – coherently combined high-power fiber lasers,

• Fastlite (France) – high-power mid-infrared OPCPA systems based on thin-disk lasers,

• Class 5 Photonics (Germany) – OPCPA systems based on slab laser architectures.