From Wikipedia, the free encyclopedia X-ray laser
X-ray laser
Xaser)
An X-ray laser (or Xaser is a device that uses stimulated addition, a pre-ionization electric or optical pulse is
emission to generate or amplify electromagnetic radia- often used. An example is the capillary neon-like
tion in the near X-ray or extreme ultraviolet region of Ar8+ laser (generating radiation at 47 nm).
the spectrum, that is, usually on the order of several of • : After being hit by an optical pulse, the target emits
tens of nanometers (nm) wavelength. highly excited plasma. Again, a longer "pre-pulse" is
Because of high gain in the lasing medium, short often used for plasma creation and a second, shorter
upper-state lifetimes (1–100 ps), and problems associated and more energetic pulse is used for further
with construction of X-ray mirrors, X-ray lasers usually excitation in the plasma volume. For short lifetimes,
operate without any resonator. The emitted radiation, a sheared excitation pulse may be needed (GRIP -
based on amplified spontaneous emission, has relatively grazing incidence pump). The gradient in the
low spatial coherence. The line is mostly Doppler broad- refractive index of the plasma causes the amplified
ened, which depends on the ions’ temperature. pulse to bend from the target surface, because at the
As the common visible-light laser transitions be- frequencies above resonance the refractive index
tween electronic or vibrational states correspond to en- decreases with matter density. This can be
ergies up to only about 10 eV, different active media are compensated for by using curved targets or multiple
needed for X-ray lasers. targets in series.
• : At optical densities high enough to cause effective
X-ray laser active media electron tunnelling, or even to suppress the
potential barrier (> 1016 W/cm2), it is possible to
The most often used media include highly ionized plas- highly ionize gas without contact with any capillary
mas, created in a capillary discharge or when a linearly or target. A collinear setup is usually used, enabling
focused optical pulse hits a solid target. In accordance the synchronization of pump and signal pulses.
with the Saha ionization equation, the most stable elec- An alternative amplifying medium is the relativistic elec-
tron configurations are neon-like with 10 electrons re- tron beam in a free electron laser, which, strictly speak-
maining and nickel-like with 28 electrons remaining. The ing, uses stimulated Compton scattering instead of stim-
electron transitions in highly ionized plasmas usually ulated emission.
correspond to energies on the order of hundreds of elec- A different approach to optically induced coherent
tron volts (eV). X-ray generation high-harmonic generation, stimulated
Thomson scattering or radiation produced by oscillating
electrons during laser wakefield acceleration.
Applications
Applications of coherent X-ray radiation include re-
search into dense plasmas (not transparent to visible ra-
diation), X-ray microscopy, phase-resolved medical
imaging, and material surface research.
See also
The vacuum chambers at the PALS laboratory in Prague, • Strategic Defense Initiative X-ray laser and Project
where a 1 kJ pulse creates plasma for X-ray generation Excalibur
• European x-ray free electron laser
• : In this setup, a several centimeters long capillary • Industrial CT scanning
made of resistant material (e.g., alumina) confines a
high-current, submicrosecond electrical pulse in a
low-pressure gas. The Lorentz force causes further
compression of the plasma discharge (see pinch). In
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From Wikipedia, the free encyclopedia X-ray laser
Categories:
• X-rays
• Laser types
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