Study of beam aberrations in a germanium XXIII XUV laser amplifier

A beam of amplified spontaneous emission at 23.2/23.6 nm from a GeXXIII XUV laser has been injected into a separate amplifier plasma and the astigmatic aberrations introduced by plasma density gradients in the amplifier have been estimated from analysis of images of the amplified beam.

Characteristics of rapidly recombining plasmas suitable for high-gain X-ray laser action

Recombining plasmas produced by picosecond laser pulses are characterized by measuring ratio of intensities of resonance lines of H- and He-like ions in the plasmas. It is found that the rapidly recombining plasmas produced by picosecond laser pulses are suitable for high-gain operation.

Development of XUV lasers at the RAL central laser facility

Recent progress in the development of XUV lasers by research teams using high-power and ultrashort-pulse Nd:glass and KrF laser facilities at the Rutherford Appleton Laboratory is reviewed. Injector-amplifier operation and prepulse enhanced output of the Ge XXIII collisional laser driven by a kilojoule glass laser, enhanced gain in CVI recombination with picosecond CPA drive pulses from a glass laser, and optical field ionization and XUV harmonic generation with a KrF CPA laser are described.

HALF-CAVITY GENERATING SATURATED EMISSION AT 236 ANGSTROM IN GERMANIUM LASER

A half-cavity using a multilayer mirror has been set up close to the end of a large gain germanium-target system. An unambiguous saturation behaviour of the 232 angstrom and 236 angstrom lines has been observed. The role of the cavity mirror in this result is discussed. Suggestions are made for practical applications of an XUV laser in this wavelength range.

COLLISION PUMPED SOFT-X-RAY LASERS - PROGRESS AT RAL

Recent developments and progress on collision pumped soft X-ray lasers using the VULCAN glass laser at Rutherford-Appleton Laboratory are presented. This includes saturated output operation of a double target germanium system within a low Fresnel number half-cavity, measurement of the spatial coherence of the output beam in the above and other geometries, use of the beam to demonstrate almost-equal-to 0.15 mum spatial resolution in a full-field microscope and initial studies of other Ne-like and Ni-like systems. Future directions, in the light of new developments of VULCAN facilities, are outlined.

NE-LIKE GE SLAB TARGET STUDIES CARRIED OUT AT RAL

The effect of non-uniform target illumination on the soft X-ray lasing output intensity of the J=2-1 Ne-like Ge transitions as a function of length was investigated. As the degree of nonunifonnity increased with length the Ne-like Ge 23.2 and 23.6 nm J=2-1 transitions did not show exponentiation of output intensity. Using an experimentally measured gain-intensity scaling relationship these results were modelled and good qualitative agreement obtained. The model indicates that for Ge targets which are non-uniformly illuminated, even with peak to valley ratios of up to 3 efficient operation can be achieved at between 2-3x threshold intensity. Further studies of the effect of increasing the separation between the two targets of a double target geometry are also presented.

SATURATED AND NEAR DIFFRACTION-LIMITED ASE OUTPUT AT 23.6 NM

Amplification of spontaneous emission at 23.6 nm has been studied in a Ge plasma heated by a 1 TW, 1.06 mum wavelength, laser pulse. The exponent of the axial gain reached 21 in a geometry with Fresnel number less-than-or-equal-to 1. Two plasma columns were produced by irradiation of slab targets up to a combined length of 3.6 cm. A narrow band XUV mirror allowed double pass amplification. Saturation of ASE output at 23.6 nm was observed as a change from exponential to linear growth of the output with plasma length. Further evidence of the effect was provided by a decline in the ratio of the output at 23.6 nm to that at 23.2 nm from approximately 1.6: 1 to approximately 0.5: 1, the latter being the theoretically predicted value for saturated operation. The onset of saturation at gL almost-equal-to 15 is consistent with model calculations. The beam divergence was about 8x diffraction limited with a brightness estimated at almost-equal-to 10(14) W/cm2/ster.

EXPERIMENTAL STUDIES OF LINE INTENSITY RATIO AS A DIAGNOSTIC OF RECOMBINING PLASMAS

Double slits have been incorporated in a flat field spectrometer to record spatially resolved and integrated spectra simultaneously. Variation of the absorbed irradiance and ionisation stage along the fibre plasmas has been monitored. By comparison of the spatially resolved and integrated resonance line ratios, it is found that the spatially integrated values deviated significantly from the real experimental circumstances due to nonuniformity along the plasmas.

MEASUREMENT OF THE PHOTO-PUMP STRENGTH OF THE 3D-5F TRANSITIONS IN THE AUTOMATICALLY LINE MATCHED NI-LIKE SM PHOTOPUMPED X-RAY LASER

The photo-pump strengths of both the ((3 (d) over bar(4))(0)(3d(6))(0))(0)-(((3 (d) over bar(3))(3/2)(3d(6))(0))(3/2)(5 (f) over bar)(5/2))(1) and the ((3 (d) over bar(4))(0)(3d(6))0)0-(((3 (d) over bar(4))(0)(3d(5))(5/2))(5/2)(5f)(7/2))(1) transitions in Ni-like Sm34+ have been measured to be 2.0 x 10(-4) and 2.4 x 10(-4) photons/mode respectively. The implications of the measurement are briefly discussed in a comparison of the merits of automatically line matched photo-pump scheme to those of the collisional excitation Ni-like Sm+34 scheme.