M.-C. Chou

Enhancement of injection and acceleration of electrons in a laser wakefield accelerator by using an argon-doped hydrogen gas jet and optically preformed plasma waveguide

A systematic experimental study on injection of electrons in a gas-jet-based laser wakefield accelerator via ionization of dopant was conducted. The pump-pulse threshold energy for producing a quasi-monoenergetic electron beam was significantly reduced by doping the hydrogen gas jet with argon atoms, resulting in a much better spatial contrast of the electron beam. Furthermore, laser wakefield electron acceleration in an optically preformed plasma waveguide based on the axicon-ignitor-heater scheme was achieved. It was found that doping with argon atoms can also lower the pump-pulse threshold energy in this experimental configuration.

Single-shot soft-x-ray digital holographic microscopy with an adjustable field of view and magnification.

Single-shot digital holographic microscopy with an adjustable field of view and magnification was demonstrated by using a tabletop 32.8 nm soft-x-ray laser. The holographic images were reconstructed with a two-dimensional fast-Fourier-transform algorithm, and a new configuration of imaging was developed to overcome the pixel-size limit of the recording device without reducing the effective NA. The image of an atomic-force-microscope cantilever was reconstructed with a lateral resolution of 480 nm, and the phase contrast image of a 20 nm carbon mesh foil demonstrated that profiles of sample thickness can be reconstructed with few-nanometers uncertainty. The ultrashort x-ray pulse duration combined with single-shot capability offers great advantage for flash imaging of delicate samples.

Seeding of a soft-x-ray laser in a plasma waveguide by high harmonic generation

A strongly saturated waveguide-based optical-field-ionization soft-x-ray laser seeded by high harmonic generation was demonstrated for Ni-like Kr lasing at 32.8 nm. Compared with the same laser seeded only with spontaneous emission, seeding with high harmonics yields much smaller divergence, enhanced spatial coherence, and controlled polarization. The integration of high harmonic seeding, optically preformed plasma waveguide, and optical-field-ionization pumping forms one of the optimal archetypes of an ultrashort-pulse soft-x-ray laser.

Experimental investigation of the parameter space for optical-field-ionization cluster-jet x-ray lasers

Optical-field-ionization collisional-excitation x-ray lasers in xenon and krypton clustered gas jets were experimentally investigated in detail. Dependence of x-ray lasing on atom density, laser focus position, and laser polarization ellipticity was mapped out to find the optimal lasing conditions, and a tomographic measurement technique was used to provide clear pictures of the x-ray amplification process.

Optical-field-ionization collisional-excitation x-ray lasers with an optically preformed plasma waveguide

Optical-field-ionization x-ray lasers in an optically preformed plasma waveguide for pure xenon, krypton, and argon gases, respectively, are achieved. In addition to the 46.9 nm main lasing line for Ne-like argon, the 45.1 and 46.5 nm lasing lines are also observed, indicative of the strong enhancement effect and the large gas density in the plasma waveguide. With this technique multispecies parallel x-ray lasing is also demonstrated in a Kr-Ar mixed-gas waveguide. Extensive experimental results including the pump-energy dependence, the density dependence, and the effects of parameters that control the waveguide fabrication are reported and discussed.

Development and application of plasma waveguide based soft x-ray lasers

Efficient soft x-ray lasing was achieved by using plasma waveguide to confine the pump beam. Seeding the laser with high-harmonic generation yields small divergence, high coherence, and controlled polarization. Application in digital holographic microscopy was demonstrated.

Development and application of plasma-waveguide based soft x-ray lasers

Efficient soft x-ray lasing was achieved by using plasma waveguide to confine the pump beam. Seeding the laser with high-harmonic generation yields small divergence, high coherence, and controlled polarization. Application in digital holographic microscopy was demonstrated.

Developments and applications of optical-field-ionization x-ray lasers at IAMS

We experimentally demonstrate the amplification of optical-field-ionization soft x-ray lasers in an optically preformed plasma waveguide for pure xenon, krypton, and argon gases, respectively. The lasing photon number of Ni-like Kr laser at 32.8 nm generated in waveguide is dramatically enhanced by about three orders of magnitude in comparison to that without plasma waveguide, resulting in a photon number of 8×1010 and an energy conversion efficiency of 2×10-6 with a pump pulse of just 235 mJ. In addition to the 46.9 nm main lasing line for Ne-like argon, the 45.1 and 46.5 nm lasing lines are also observed, indicative of the strong enhancement effect and the large gas density in the plasma waveguide. With this technique multispecies parallel x-ray lasing is also demonstrated in a Kr-Ar mixed-gas waveguide. By seeding optical-field-ionization plasma with high harmonic signals, 32.8-nm Kr laser output can be further improved to produce brighter and better collimated x-ray laser beams. Comparing with the same laser seeded only with spontaneous emission, seeding with high harmonics yields much smaller divergence, enhanced spatial coherence, and controlled polarization. With the illumination of high-brightness 32.8-nm x-ray laser pulses, single-shot x-ray digital holographic microscopy with an adjustable field of view and magnification is demonstrated successfully. The ultrashort x-ray pulse duration combined with single-shot capability offers great advantage for flash imaging of delicate samples.

High Brightness Optical-Field-Ionization X-Ray Lasers Driven in Plasma Waveguides

We experimentally demonstrate that the plasma waveguide can be efficiently produced in a pure Xe, Kr, and Ar cluster jet operated at a high backing pressure with axicon ignitor-heater scheme. The lasing photon number of Ni-like Kr laser at 32.8 nm generated in waveguide is dramatically enhanced by about three orders of magnitude in comparison to that without plasma waveguide, resulting in a photon number of 8×1010 and an energy conversion efficiency of 2×10−6 with a pump pulse of just 235 mJ. Due to the high atom density and long gain length provided by the plasma waveguide, Ne-like Ar laser at 46.9 nm is achieved in OFI plasma channel at the first time and simultaneous lasing in two ion species is also generated in a 10-mm gas jet with Kr and Ar mixtures. With sufficient x-ray photons, we show that x-ray digital holographic microscopy can be achieved in single-shot measurement providing a spatial resolution of >500 nm and a temporal resolution of >10 ps.

Ultrashort pulse driven optical-field-ionization x-ray lasers

Efficient optical-field-ionization x-ray lasers driven by femtosecond laser pulses have been demonstrated in clustered gas jets. With a tight focusing configuration, near saturation outputs of Pd-like xenon laser at 41.8 nm and Ni-like krypton laser at 32.8 nm are generated at low pump energy of 200 mJ. By using the axicon-ignitor-heater scheme to produce a 9-mm-long plasma waveguide in a pure krypton gas jet, the lasing photon number of Ni-like Kr laser at 32.8 nm is dramatically enhanced by about three orders of magnitude in comparison to that without plasma waveguide, resulting in a photon number of 8×1010 and an energy conversion efficiency of 2×10-6 with a pump pulse of just 235 mJ. Besides for producing various OFI collisional-excitation x-ray lasers of sufficient photon number for practical applications, an optically-preformed plasma waveguide may also be a favorable choice for achieving OFI recombination x-ray lasers and inner-shell x-ray lasers.