Making molecular X-rays as easy as chest X-rays
The use of lasers provides an intriguing opportunity to produce a compact, tabletop X-ray microscopy system to image living systems. Laser light is monochromatic, implying that it has single colour, single frequency and single wavelength. Technological advances have significantly extended the range of possible wavelengths from the visible spectrum to the ultraviolet (UV) and mid-infrared (IR) ranges. Extending that range into the X-ray realm is possible using high harmonic generation (HHG). HHG can convert the laser’s frequency into its multiples to generate a broad spectrum of light that includes UV and X-ray frequencies. Although HHG has been around since the 1980s, producing intense and focused radiation above photon energies of 100 electron Volts (eV) is still difficult. To make detailed biological imaging possible, scientists needed to overcome this technical challenge. They focussed on using a water window as soft X-rays are transparent in water whereas elements such as carbon (abundant in biological specimens) absorb it. The EU-funded BAXHHG project contributed significantly to the advancement of laser technology with ultrafast lasers for producing tabletop X-ray systems that image biological systems. Although work is still in progress, scientists generated photon energies up to 200 eV with mid-IR light (of 2 micron wavelength) using neon and argon. Scientists also developed important computer models to simulate HHG, an intrinsically inefficient process. They also developed and tested an apparatus for containing high pressures within a vacuum chamber to optimise HHG. BAXHHG scientists made important progress in opening the window to novel tabletop X-ray technology to provide detailed structural information about biological specimens. Generation of high-energy photons in extremely intense and focused beams within the water window will enable fast and inexpensive visualisation of fine structural detail. This could play an important role in the cost-effective development of drugs and other targeted therapies.
