X-RAY LASER DEVELOPMENT AT GSI
X-RAY LASER CHARACTERISTICS
- Wavelength: 7 to 24 nm
- Monochromaticity: dλ/λ ~ 10-5
- High instantaneous brightness:
- Photon number ~ 1011/pulse
- Pulse duration ~ 1 ps
- Divergence ~ 25 mrad²
- Source size ~ 0.0001 mm²
- Temporal and spatial coherence
- High repetition-rate: up to 10 Hz
TRANSIENT COLLISONALLY EXCITED X-RAY LASERS
Laser produced plasma based nickel-like transient collisonally excited (TCE) x-ray lasers use the highly ionized hot plasma as the laser medium to generate gain in the x-ray regime.
The creation of the target plasma and its ionisation up to the Ni-like state is done by electron-ion collisions induced by a short laser pulse. Then the population inversion for the lasing transition is produced by electron-electron collision induced by another short laser pulse.
X-RAY LASER PUMPING
The double-pulse non-normal incidence pumping geometry is the scheme to generate x-ray lasers in a very reliable and stable way at high output power.
The stretched oscillator pulse is injected into a Mach-Zehnder unit to create an optimized double-pulse, which is then amplified and compressed revealing its final temporal shape. This double CPA laser pulse is sent into the target chamber and focused by spherical mirror to a line focus on the target material to generate the x-ray laser emission. Additionally high order harmonics are produced by a short pulse laser focus in a gas tube to seed the x-ray laser amplifier.
Double-pulse generation with the Mach-Zehnder unit and the chirped pulse amplification and the compression in the laser system.
Grazing incidence pumping (GRIP) of the main pulse to optimize the energy deposition in the pre-plasma.
Traveling-wave excitation along the line focus to match the transient gain of the x-ray amplifier.
X-RAY LASER SPECTRA
The spectra of x-ray lasers and high order harmonics reach from the extreme ultra violet EUV (100nm – 10nm) down to the soft x-ray regime (10nm – 1nm).
The Ni-like yttrium laser at 24nm (51eV), the Ni-like zirconium laser at 22nm (56eV), the Ni-like molybdenum at 18.9nm (65eV), the Ni-like palladium laser at 14.7nm (84eV), and the Ni-like silver laser at 13.9nm (89eV) represent lasers in the EUV.
The Ni-like samarium laser at 7.3nm (168eV) is operating in the soft x-ray regime.
High order harmonics in argon cover the EUV down to 19nm (65eV).
OUTLOOK: SEEDED MULTI X-RAY AMPLIFIER FOR APPLICATIONS
The coherent ultra short high order harmonic soft x-ray source is sent into x-ray amplifiers and is then focused onto the target (i.e. biological molecules).