- The paper demonstrates a phase-matched high-harmonic generation technique that produces near-unity spatial coherence verified via double-pinhole interference.
- The experiment utilizes a hollow-core fiber with 25 fs Ti:sapphire pulses to achieve a diffraction-limited beam featuring less than 1 mrad divergence.
- These advancements enable compact EUV holography and pave the way for high-precision metrology, microscopy, and stroboscopic imaging applications.
Summary of "Generation of Spatially Coherent Light at Extreme Ultraviolet Wavelengths"
This paper presents a detailed paper on the generation of spatially coherent light at extreme ultraviolet (EUV) wavelengths using high-harmonic generation (HHG). The authors utilize a phase-matched hollow-fiber geometry to demonstrate nearly full spatial coherence of the EUV beam produced. This advancement allows for the realization of EUV holography in compact tabletop setups and opens pathways for various applications including high-precision metrology and microscopy with nanometer resolution.
The research addresses a significant challenge in the field where traditional methods of generating EUV light, such as synchrotrons and free-electron lasers, only achieve partial coherence. The paper elucidates the mechanisms behind HHG, explaining how the interaction between high-intensity femtosecond pulses and a gaseous medium creates focused coherent beams. However, achieving full coherence has been historically problematic due to factors like plasma refraction and varying phases of emitted light.
A notable advancement in this research is the use of a hollow-core fiber to maintain phase matching over an extended interaction region, enhancing the temporal and spatial coherence. The authors quantitatively measure the spatial coherence using a double-pinhole interference method, finding unity coherence across much of the beam diameter. They report a beam divergence of less than 1 mrad and a diffraction-limited source size of approximately 40 µm diameter, with a photon flux of about 2 x 10 photons/second.
The experimental setup is outlined in detail, including a high repetition rate Ti:sapphire laser system operating at 760 nm with a pulse duration of 25 fs, focused into a fiber filled with argon gas. The resultant EUV radiation, phase-matched at specific pressures, produces harmonics centered around 31 eV with photon energies corresponding to harmonic orders between 17 and 23.
From the experimental data, the paper discusses the fringe visibility obtained using different pinhole separations, demonstrating maintained spatial coherence over most of the EUV beam. The paper highlights the capability of recording Gabor holograms of small objects, demonstrating the applicability for high-resolution coherent imaging. The research explores the potential for further resolution improvements and applications, such as high-precision metrology and EUV lithography.
The implications of this research are extensive. The ability to generate coherent EUV light on a tabletop scale represents a significant step forward in the accessibility of high-resolution imaging technologies. The paper suggests future possibilities for stroboscopic holography with temporal resolutions defined by the EUV pulse durations, inviting further investigation in applications requiring ultrahigh time resolutions.
In conclusion, this paper not only provides substantial technical results regarding the coherence measurement and generation but also paves the way for practical advancements in various scientific fields utilizing coherent EUV light. Future research may focus on optimization for enhanced coherence and exploring novel applications leveraging the compact and coherent nature of the EUV source.