Few-Cycle Yb-Doped Laser Sources for Attosecond Science and Strong-Field Physics

Quantum Physics Optics Physics
Yb-doped lasers attosecond science strong-field physics nonlinear compression high-order harmonic generation

Background

Attosecond science is a cutting-edge field that studies the ultrafast dynamics of electrons in atoms, molecules, and solids. Since the discovery of High-Order Harmonic Generation (HHG) and the experimental realization of attosecond pulses, attosecond science has rapidly advanced, becoming a powerful tool for investigating electron dynamics. However, traditional Titanium-Sapphire (Ti:Sapphire, Ti:Sa) lasers, although excellent for HHG and attosecond pulse generation, are limited in high-repetition-rate and high-average-power applications due to their high quantum defect and thermal load. In recent years, Ytterbium (Yb)-doped lasers have emerged as a new tool in attosecond science due to their low quantum defect, high repetition rate, and high average power. This paper explores the applications of Yb-doped lasers in attosecond science and reviews recent advancements in nonlinear compression, attosecond pulse generation, and electric field measurement.

Source of the Paper

This paper is co-authored by Tran-Chau Truong, Dipendra Khatri, Christopher Lantigua, Chelsea Kincaid, and Michael Chini, affiliated with The Ohio State University and the University of Central Florida. Published on April 16, 2025, in APL Photonics, the paper is titled “Few-cycle Yb-doped laser sources for attosecond science and strong-field physics” and is part of the special collection “Advances Enabled by Ytterbium: From Advanced Laser Technology to Breakthrough Applications.”

Main Content of the Paper

1. Advantages and Applications of Yb-Doped Lasers

Yb-doped lasers, with their low quantum defect and high efficiency, can operate at high repetition rates and high average power, making them suitable for both industrial applications and attosecond science. Compared to Ti:Sapphire lasers, Yb-doped lasers exhibit higher stability and lower maintenance requirements in thin-disk and fiber laser geometries. However, the narrow gain bandwidth of Yb-doped lasers results in longer pulse durations (>100 fs to >1 ps), making them unsuitable for direct attosecond pulse generation. Therefore, Yb-doped lasers were initially used as pump sources for few-cycle Optical Parametric Amplifiers (OPA) and Optical Parametric Chirped Pulse Amplifiers (OPCPA).

2. Nonlinear Compression Techniques

To generate few-cycle pulses, researchers have developed various nonlinear compression techniques, including Hollow-Core Capillary Fiber (HCF) and Multi-Pass Cell (MPC). HCF achieves spectral broadening through Self-Phase Modulation (SPM) by propagating laser pulses in gas-filled capillaries, followed by dispersion compensation to compress the pulses. MPC, on the other hand, achieves spectral broadening by repeatedly focusing the beam within a nonlinear medium, offering higher energy efficiency and shorter pulse durations. In recent years, MPC technology has made significant progress in compressing high-average-power and high-energy pulses, achieving compression efficiencies of up to 98% and pulse durations as short as a few femtoseconds.

3. Attosecond Pulse Generation

Attosecond pulse generation is primarily achieved through High-Harmonic Generation (HHG). The high repetition rate and high average power of Yb-doped lasers provide higher photon flux and shorter data acquisition times for HHG, making them particularly suitable for experiments requiring low photon counts, such as coincidence electron and ion detection and surface photoemission spectroscopy. Through nonlinear compression techniques, Yb-doped lasers can generate few-cycle pulses, driving HHG to produce broadband attosecond pulses. Experiments have shown that Yb-doped lasers can generate harmonic energies up to 350 eV in helium, with photon fluxes as high as 10^5 photons/s.

4. Electric Field Measurement Techniques

In addition to generating attosecond pulses, direct measurement of the electric field waveform of ultrashort laser pulses provides a new approach for attosecond science. Optical field sampling techniques use fast temporal gates to directly measure sub-cycle dynamics of the electric field without the need for complex reconstruction algorithms. In recent years, electric field measurement techniques based on strong-field responses, such as tunnel ionization and multiphoton excitation in solids, have enabled ambient-condition measurements of electric fields in the petahertz to near-infrared frequency range. These techniques offer new tools for attosecond science, enabling the exploration of ultrafast phenomena such as electron dynamics and quantum vacuum fluctuations.

Significance and Value of the Paper

This paper reviews the applications of Yb-doped lasers in attosecond science, showcasing their recent advancements in nonlinear compression, attosecond pulse generation, and electric field measurement. The high repetition rate and high average power of Yb-doped lasers provide a new experimental platform for attosecond science, enabling high photon flux and short data acquisition times, particularly suitable for complex spectroscopic techniques and multidimensional spectral measurements. Moreover, the stability and efficiency of Yb-doped lasers make them ideal for laboratory-scale attosecond sources, promising to advance attosecond technology in fields such as physics, chemistry, and biology.

Research Highlights

  1. High Repetition Rate and High Average Power: Yb-doped lasers can operate at high repetition rates (kHz to MHz) and high average power (kW level), providing higher photon flux and shorter data acquisition times for attosecond science.
  2. Nonlinear Compression Techniques: Through HCF and MPC techniques, Yb-doped lasers can generate few-cycle pulses, driving HHG to produce broadband attosecond pulses.
  3. Electric Field Measurement Techniques: Electric field measurement techniques based on strong-field responses provide new tools for attosecond science, enabling direct measurement of sub-cycle dynamics of the electric field.
  4. Application Prospects: The stability and efficiency of Yb-doped lasers make them ideal for laboratory-scale attosecond sources, promising to advance attosecond technology in various fields.

Conclusion

The application of Yb-doped lasers in attosecond science demonstrates their significant potential in nonlinear compression, attosecond pulse generation, and electric field measurement. With continuous advancements in Yb-doped laser technology, attosecond science will embrace new development opportunities, driving deeper understanding of electron dynamics and research into complex systems.