The article "Bright Coherent Ultrahigh Harmonics in the keV X-Ray Regime from Mid-Infrared Femtosecond Lasers" by T. Popmintchev et al. presents a novel method for generating bright, coherent ultrahigh harmonics in the keV X-ray regime using mid-infrared femtosecond lasers. The authors demonstrate that by focusing a mid-infrared laser pulse into a high-pressure gas, ultrahigh harmonics can be generated up to orders greater than 5000, resulting in a supercontinuum spanning the entire electromagnetic spectrum from the ultraviolet to over 1.6 keV. This allows for the generation of pulses as short as 2.5 attoseconds. The multi-atmosphere gas pressures required for efficient phase matching also support laser beam self-confinement, enhancing the X-ray yield. Despite the high pressure and density, the X-ray beam exhibits high spatial coherence, even though the electrons responsible for high harmonic generation encounter many neighboring atoms during the emission process. The study highlights the unique ability of X-rays to capture structure and dynamics at the nanoscale, making this technique promising for advanced spectroscopy and imaging applications.The article "Bright Coherent Ultrahigh Harmonics in the keV X-Ray Regime from Mid-Infrared Femtosecond Lasers" by T. Popmintchev et al. presents a novel method for generating bright, coherent ultrahigh harmonics in the keV X-ray regime using mid-infrared femtosecond lasers. The authors demonstrate that by focusing a mid-infrared laser pulse into a high-pressure gas, ultrahigh harmonics can be generated up to orders greater than 5000, resulting in a supercontinuum spanning the entire electromagnetic spectrum from the ultraviolet to over 1.6 keV. This allows for the generation of pulses as short as 2.5 attoseconds. The multi-atmosphere gas pressures required for efficient phase matching also support laser beam self-confinement, enhancing the X-ray yield. Despite the high pressure and density, the X-ray beam exhibits high spatial coherence, even though the electrons responsible for high harmonic generation encounter many neighboring atoms during the emission process. The study highlights the unique ability of X-rays to capture structure and dynamics at the nanoscale, making this technique promising for advanced spectroscopy and imaging applications.