M. Berrill

Saturated high-repetition-rate 18.9-nm tabletop laser in nickellike molybdenum

We report saturated operation of an 18.9-nm laser at 5-Hz repetition rate. An amplification with a gain-length product GL of 15.5 is obtained in the 4d 1S0-4p 1P1 laser line of Ni-like Mo in plasmas heated at grazing incidence with approximately 1-J pulses of 8.1-ps duration from a tabletop laser system. Lasing is obtained over a broad range of time delays and pumping conditions. We also measure a GL of 13.5 in the 22.6-nm transition of the same ion. The results are of interest for numerous applications requiring high-repetition-rate lasers at wavelengths below 20 nm.

High-energy 13.9 nm table-top soft-x-ray laser at 2.5 Hz repetition rate excited by a slab-pumped Ti:sapphire laser

We have demonstrated repetitive operation of a table-top lambda=13.9 nm Ni-like Ag soft-x-ray laser that generates laser pulses with 10 microJ energy. The soft-x-ray laser is enabled by a Ti:sapphire laser pumped by high-repetition-rate frequency-doubled high-energy Nd:glass slab amplifiers. Soft-x-ray laser operation at 2.5 Hz repetition rate resulted in 20 microwatt average power.

Warm photoionized plasmas created by soft-x-ray laser irradiation of solid targets

We report the first experimental study of plasmas created by photoionization of solid targets with focused soft X-ray laser light. The plasma properties are dominantly determined by material absorption, in agreement with model simulations.

Gain-saturated 10.9 nm tabletop laser operating at 1 Hz repetition rate

We report the demonstration of a gain-saturated 10.9 nm tabletop soft x-ray laser operating at 1 Hz repetition rate. Lasing occurs by collisional electron impact excitation in the 4dS01-->4pP11 transition of nickel-like Te in a line-focus plasma heated by a chirped-pulse-amplification Ti:sapphire laser. With an average power of 1muW and pulse energy up to approximately 2microJ, this laser extends the ability to conduct tabletop laser experiments to a shorter wavelength.

Highly coherent injection-seeded 13.2 nm tabletop soft x-ray laser

We report a dramatic improvement of the spatial coherence and beam divergence (0.66 mrad) of a 13.2 nm wavelength Ni-like Cd tabletop laser by injection seeding the soft x-ray laser amplifier with high-harmonics pulses generated in a Ne gas jet. This phase coherent laser is an attractive light source for at-wavelength interferometry of extreme ultraviolet lithography optics and other applications.

High repetition rate operation of saturated tabletop soft x-ray lasers in transitions of neon-like ions near 30 nm

We report average powers exceeding 1 microwatt in laser transitions of Ne-like ions at wavelengths near 30 nm. Gain-saturated operation was obtained at a repetition rate of 5 Hz exciting solid targets with pump pulses of ~1 J energy and 8 ps duration impinging at grazing incidence of 20 degrees. Gain-length products of about 20 were obtained in the 30.4 nm and 32.6 nm transitions of Ne-like V and Ne-like Ti respectively. Strong lasing was also observed in Ne-like Cr at 28.6 nm and in the 30.1 nm line of Ne-like Ti.

Characteristics of a saturated 18.9-nm tabletop laser operating at 5-Hz repetition rate

We report the characteristics of a saturated high-repetition rate Ni-like Mo laser at 18.9 nm. This table-top soft X-ray laser was pumped at a 5-Hz repetition rate by 8-ps 1-J optical laser pulses impinging at grazing incidence into a precreated Mo plasma. The variation of the laser output intensity as a function of the grazing incidence angle of the main pump beam is reported. The maximum laser output intensity was observed for an angle of 20/spl deg/, at which we measured a small signal gain of 65 cm/sup -1/ and a gain-length product g/spl times/l>15. Spatial coherence measurements resulting from a Youngs double-slit interference experiment show the equivalent incoherent source diameter is about 11 /spl mu/m. The peak spectral brightness is estimated to be of the order of 1/spl times/10/sup 24/ photons s/sup -1/ mm/sup -2/ mrad/sup -2/ within 0.01% spectral bandwidth. This type of practical, small scale, high-repetition soft X-ray laser is of interest for many applications.

Temporal coherence and spectral linewidth of an injection-seeded transient collisional soft x-ray laser

The temporal coherence of an injection-seeded transient 18.9 nm molybdenum soft x-ray laser was measured using a wavefront division interferometer and compared to model simulations. The seeded laser is found to have a coherence time similar to that of the unseeded amplifier, ~1 ps, but a significantly larger degree of temporal coherence. The measured coherence time for the unseeded amplifier is only a small fraction of the pulsewidth, while in the case of the seeded laser it approaches full temporal coherence. The measurements confirm that the bandwidth of the solid target amplifiers is significantly wider than that of soft x-ray lasers that use gaseous targets, an advantage for the development of sub-picosecond soft x-ray lasers.

Pulse duration measurements of grazing-incidence-pumped high repetition rate Ni-like Ag and Cd transient soft x-ray lasers.

We have measured the pulse duration of gain-saturated 13.9 nm Ni-like Ag and 13.2 nm Ni-like Cd transient collisional lasers excited by grazing-incidence-pumping for several pumping conditions. High-resolution streak-camera measurements yielded FWHM pulse durations close to 5 ps for both lasers under optimum pumping conditions. The very high brightness and short pulse duration of these new high repetition tabletop soft x-ray lasers make them an attractive source for dynamic applications.

Improved beam characteristics of solid-target soft x-ray laser amplifiers by injection seeding with high harmonic pulses

Injection seeding of solid-target soft x-ray laser amplifiers with high harmonic pulses is shown to dramatically improve the far-field laser beam profile and reduce the beam divergence. Measurements and two-dimensional simulations for a 13.9 nm nickel-like Ag amplifier show that the amplified beam divergence depends strongly on the seed and can therefore be controlled by selecting the divergence of the seed. The near-field beam size of both the seeded and unseeded lasers is shown to be determined by the size of the gain region and the divergence of the amplified beams.