High-order harmonic generation (HHG) provides a compact means of creating attosecond pulses, essential tools for investigating the ultra-fast dynamics of atoms and molecules. Researchers Feng Wang, Chunhui Yang, and Xinyi Cui, alongside colleagues Lixin He, Tianxin Ou, and Rui-Bo Jin, have now demonstrated a method for actively controlling the pathways that contribute to harmonic emission during HHG. The team achieves this control by employing squeezed light, a special state of light with reduced fluctuations, to selectively suppress either the long or short path contributing to harmonic generation. This path control, stemming from the unique fluctuations within squeezed light and their effect on phase matching, opens the possibility of generating extremely short, isolated attosecond pulses, potentially reaching durations of less than one atomic unit of time and promising significant advances in attosecond science.
Harmonic generation (HHG), a robust tabletop source for producing attosecond pulses, has become a cornerstone of attosecond metrology. Traditionally, HHG driven by classical laser fields relies on two quantum pathways, termed short and long, which contribute to the emission of harmonics. Recent research demonstrates that these quantum pathways in HHG can be selectively controlled using squeezed light, a unique form of non-classical light. The results reveal that the long quantum path of HHG is dramatically suppressed in phase-squeezed fields, while the short quantum path is suppressed in amplitude-squeezed fields. This quantum path control stems from the inherent quantum fluctuations within the squeezed light itself.
Attosecond Pulse Generation via High Harmonics
High-harmonic generation (HHG) is a powerful technique for creating attosecond pulses and imaging materials with nanoscale resolution. This process involves driving a gas with an intense laser, generating high-frequency light. Attosecond science, which studies electron dynamics on the attosecond timescale, relies heavily on HHG as a key enabling technology. The interaction of intense laser fields with matter, including ionization and harmonic generation, forms the basis of strong-field physics. Researchers are increasingly exploring the use of squeezed states and quantum entanglement to enhance HHG efficiency and improve the quality of the generated harmonics. Imaging techniques based on HHG, such as microscopy and spectroscopy, are being developed to probe materials with unprecedented resolution.
Squeezed Light Controls Harmonic Quantum Pathways
Researchers have demonstrated precise control over the quantum pathways involved in high-order harmonic generation (HHG), a process used to create isolated attosecond pulses of light. By employing squeezed light, a special type of non-classical light, the team selectively suppressed either the short or long quantum path contributing to harmonic emission. Time-frequency analysis revealed that this path control arises from fluctuations inherent in the squeezed light, effectively modifying the conditions for harmonic generation from different quantum states. This ability to control quantum pathways extends across the entire harmonic plateau, offering the potential to generate extremely short, isolated attosecond pulses with durations potentially less than one atomic unit of time.
Such pulses would enable investigations of electron dynamics in various materials with unprecedented temporal resolution. This breakthrough promises the potential for generating isolated attosecond pulses with durations less than one atomic unit of time, significantly shorter than the currently achievable 43 attosecond pulses. By controlling quantum pathways across the entire harmonic plateau, scientists can overcome limitations in achieving ultrashort pulse durations, paving the way for advancements in attosecond metrology and ultrafast imaging of electronic dynamics. The study confirms that manipulating the quantum statistics of the driving light source offers a novel approach to tailoring the properties of generated harmonics and achieving unprecedented control over attosecond pulse shaping.
Squeezed Light Controls Harmonic Quantum Pathways
Looking ahead, the researchers suggest that the inherent quantum path control offered by this method could facilitate the development of high harmonic spectroscopy, allowing for detailed probing of ultrafast electronic processes in quantum light itself.