Plasma-based X-ray laser at 21 nm for multidisciplinary applications

An overview of recent advances in applications of currently the most energetic X-ray laser at 21 nm is given. The unique parameters of this half-cavity based X-ray laser such as record output energy of 10 mJ, highly symmetric beam, robustness and reproducibility, have made it possible to carry out a number of multidisciplinary scientific projects featuring novel applications of intense coherent X-ray radiation. Selected results obtained in these experiments are reviewed, including X-ray laser probing of dense plasmas, measurements of transmission of focused soft X-ray radiation at intensities of up to 10¹² W cm^-2, measurements of infrared laser ablation rates of thin foils, and ablative microstructuring of solids.     

X-ray spectra from laser produced highly ionized hafnium plasma in the 4.1–4.5 Å range

X-ray spectra of highly ionized hafnium atoms have been obtained from laser produced plasmas in the 4.1–4.5 Å range. Using quasi-relativistic configuration interaction calculations of the wavelengths and transition probabilities, the observed spectral band structure can be interpreted as being due to 3d–6f transitions of the NiI—GeI like ionization states of hafnium.     

Multi-energy four-channel Kirkpatrick–Baez microscope for X-ray imaging diagnostics at the Shenguang-II laser facility

A four-channel Kirkpatrick–Baez microscope working at multiple energy bands is developed for multiframe X-ray imaging diagnostics at the Shenguang-II laser facility. The response to the multiple energy bands is realized by coating the double-periodic multilayers on the reflected surfaces of the microscope. Because of the limited size of the microstrips in the X-ray framing camera, the image separation is controlled by the conical angle of the reference cores during microscope assembly. This study describes the optical and multilayer design, assembly, and alignment of the developed microscope. The microscope achieves a spatial resolution of 4–5 mm in the laboratory and 10–20 mm at Shenguang-II laser facility within a 300 mm field of view. The versatile nature of the developed microscope enables the multiple microscopes currently installed in the laser facility to be replaced with a single, multipurpose microscope.     

Ar ion laser pumped dye-laser emission to 9500 Å

CW dye laser emission has been observed up to 9500 Å by using an Ar ion laser-pumped jet-stream dye laser. Peak powers as high as 300 mW were obtained around 8600 Å at a pump power of 4.4W.     

Lasing at 139 Å in nickel-like silver plasmas

Today, one of the key applications for X-ray Lasers is ICF-relevant plasma density diagnostics through interferometry techniques. Due to the peak reflectivity of the involved Mo/Si multilayer optics, the CEA/DAM studies have been focused on collisionnally excited population inversions in Ni-like silver plasmas. In order to optimize their X-ray output at 139 Å, various configurations have been investigated. One of them has recently been demonstrated at the P102 facility and has allowed 10¹¹ photons per pulse to be delivered, i.e. 2 μJ in 7 ps.     

Diode-side-pumped Nd:GGG laser at 1,105?nm and frequency-doubled laser at 552?nm

A high-power diode-side-pumped 1,105?nm Nd:GGG laser and a laser at 552?nm based on intracavity frequency doubling of 1,105?nm laser are demonstrated for the first time. A 26.8-W 1,105?nm laser continuous wave output was achieved under the incident pump power of 170?W. A LiB₃O₅ crystal is used for second harmonic generation of 1,105?nm laser. When the pump power was 170?W, the average output power at 552?nm of 7.3?W was obtained, corresponding to the optical conversion efficiency of 4.3?%. And the minimum pulse width is 181?ns with the pulse repetition rate of 10?kHz. The M ² factors are measured to be 19.8 and 17.6 in the horizontal and vertical directions, respectively.     

Femtosecond X-ray generation through relativistic electron beam–laser interaction

Methods for generating ultra-short X-rays using the interaction of intense laser pulses with relativistic electron beams, and their application to measuring ultra-fast phenomena in solid state materials, are reviewed. Two different methods that use a long electron bunch and short laser pulse are discussed: Thomson scattering and optical slicing which have been implemented on linac and storage ring beams, respectively. The possibility of generating ultrashort electrons bunches from laser-plasma injectors is discussed.     

Generation of passively Q-switched fiber laser at 1 μm by using Mo SSe as a saturable absorber

Passively Q-switched ytterbium-doped fiber lasers(YDFLs) incorporating a molybdenum sulfide selenide(Mo SSe)-based saturable absorber(SA) are demonstrated. The modulation depth and saturation intensity of the Mo SSe-based SA are measured to be approximately 25.0% and 0.002 MW∕cm2, respectively, using the twin detector technique. The YDFL's output has a center wavelength of 1038.5 nm with a top pulse width and energy of 1.2 μs and 18.9 nJ, respectively, at a pump power of 333 mW. The Mo SSe-based SA has a good linear optical response, providing significant opportunity for use in applications over an ultra-broadband spectrum, particularly spectroscopy and biomedical diagnostics.     

Near diffraction limit output and gain saturation of soft X-ray laser

Abstract: By using of travelling wave amplification, we have got a soft x-ray laser with near diffraction limit output and gain saturation in the experiment of four series coupling targets with reflector.     

Near diffraction limit output and gain saturation of soft X-ray laser

By using of travelling wave amplification, we have got a soft x-ray laser with near diffraction limit output and gain saturation in the experiment of four series coupling targets with reflector.     

Generation of femtosecond X-ray pulses via laser–electron beam interaction

The generation of femtosecond X-ray pulses will have important scientific applications by enabling the direct measurement of atomic motion and structural dynamics in condensed matter on the fundamental time scale of a vibrational period. Interaction of femtosecond laser pulses with relativistic electron beams is an effective approach to generating femtosecond pulses of X-rays. In this paper we present recent results from proof-of-principle experiments in which 300 fs pulses are generated from a synchrotron storage ring by using an ultrashort optical pulse to create femtosecond time structure on the stored electron bunch. A previously demonstrated approach for generating femtosecond X-rays via Thomson scattering between terawatt laser pulses and relativistic electrons is reviewed and compared with storage-ring based schemes.     

Prospects of “water-window” X-ray emission from subpicosecond laser plasmas

Soft-X-radiation in the “water-window” region (23.3–43.6 ?) mainly from carbon laser plasmas generated by subpicosecond (700 fs) 0.248-μm laser pulses is studied as a function of angle of incidence and intensity (up to 10¹⁸ W/cm²) for p-polarized laser light. Furthermore, comparison is made between plasmas generated from massive and foil targets. Numerical calculations are performed using a hydrocode coupled to X-ray line and continuum emission calculations including radiation transport. The optimized conditions to achieve maximum water-window X-ray emissivity and, in particular, carbon Lyman-α line emission are investigated. In addition, analytical scalings are presented. These theoretical results are essentially confirmed by previous experiments. It is found that at optimized conditions, picosecond or subpicosecond laser plasma X-ray sources with a power of the order of 1–10 GW in a spectral window of 1 ? could be developed. Received: 6 August 1998 / Final version: 6 August 1999 / Published online: 30 November 1999     

Random fiber laser operating at 1,115 nm

We experimentally demonstrate a random fiber laser operating at 1,115 nm using a LD-pumped Yb-doped fiber laser as the pump source. We achieve about 270 mW lasing output in a 50 km standard communication optical fiber with slope efficiency more than 28 %. A new wavelength is provided for the application of random distributed feedback fiber lasers as light sources.     

LD-pumped passively Q-switched red laser at 660 nm

A laser diode (LD) pumped Nd:YAG red pulse laser at 660 mn was presented by V:YAG passively Q-switching and LBO intracavity frequency doubling. With 1.6-W incident pump power, average output power of 46-mW, pulse duration (FWHM) of 23.3 ns, pulse repetition rate of 21.6 kHz, peak power of 91.4 W, and single pulse energy of 2.13 μJ were obtained. The beam quality factor M2 was less than 1.2. The fluctuations of pulse energy and repetition rate were less than 3% in 4 hours. The pulsed laser at 660 nm is expected to be used as the pump source of Cr3+:doped crystal to obtain the gain-switched tunable laser.     

Diode-pumped Tm:LuAG laser at room temperature

The lasing characteristics of Tm:LuAG at room temperature are reported.The maximum output power at 2.023-μm wavelength is 4.91 W and the slope efficiency is 25.39%.The mode matching between pump mode and laser mode is optimized by changing the pump beam waist radius and its location.Different output couplers are used to realize the optimal laser output.The relationship between operation temperature and output power is also discussed.     

Tunable electronic Raman laser at 16 μm

6s–9s electronic Raman scattering in caesium vapour is used to generate tunable 16m radiation. Output energies in excess of 8 J were obtained, with peak powers in the kilowatt range.     

Pulse laser ablation at water–air interface

We studied a new pulse laser ablation phenomenon on a liquid surface layer, which is caused by the difference between the refractive indices of the two materials involved. The present study was motivated by our previous study, which showed that laser ablation can occur at the interface between a transparent material and a gas or liquid medium when the laser pulse is focused through the transparent material. In this case, the ablation threshold fluence is reduced remarkably. In the present study, experiments were conducted in water and air in order to confirm this phenomenon for a combination of two fluid media with different refractive indices. This phenomenon was observed in detail by pulse laser shadowgraphy. A high-resolution film was used to record the phenomenon with a Nd:YAG pulse laser with 10-ns duration as a light source. The laser ablation phenomenon on the liquid surface layer caused by a focused Nd:YAG laser pulse with 1064-nm wavelength was found to be followed by the splashing of the liquid surface, inducing a liquid jet with many ligaments. The liquid jet extension velocity was around 1000 m/s in a typical case. The liquid jet decelerated drastically due to rapid atomization at the tips of the ligaments. The liquid jet phenomenon was found to depend on the pulse laser parameters such as the laser fluence on the liquid surface, laser energy, and laser beam pattern. The threshold laser fluence for the generation of a liquid jet was 20 J/cm². By increasing the incident laser energy with a fixed laser fluence, the laser focused area increased, which eventually led to an increase in the size of the plasma column. The larger the laser energy, the larger the jet size and the longer the temporal behavior. The laser beam pattern was found to have significant effects on the liquid jet’s velocity, shape, and history.     

Pressure broadening of methane lines in the 6190Åand 6825Åbands at room and low temperatures

Measurements of pressure broadened half-widths have been performed for one vibration-rotation line in the 6190Åmethane band and one vibration-rotation line in the 6825Åmethane band. Self-, nitrogen-, hydrogen- and helium-broadening have been measured over a temperature range of 77–295 K. Pressure broadening coefficients and temperature dependence indices have been obtained for each line and broadening gas.     

The polarized spectrum of benzene-d 6 single crystal at 2000 Å

The Roothaan open-shell LCAO-MO-SCF method was coupled with the Simons model potential in calculations of internuclear distances and ionization potentials for Li₃, Na₃, K₃, Rb₃, and Cs₃ taking core polarization into account.