G. Kulcsar

High-contrast terawatt chirped-pulse-amplification laser that uses a 1-ps Nd:glass oscillator

We have developed a fiberless 1-TW all-Nd:glass chirped-pulse-amplification laser system that uses high-contrast 0.8-1.4-ps pulses produced directly from a Nd:glass feedback-controlled oscillator. Employing grating-only expansion and compression, the system produces clean (~10(7) contrast ratio) 1-J, 1- 1.4-ps recompressed pulses without added pulse cleaning. Clean microjoule-energy pulses from the oscillator require less subsequent amplification than cw oscillator schemes, thereby minimizing gain-bandwidth narrowing and offering improved contrast with amplified stimulated emission background.

Picosecond pumping of extreme-ultraviolet lasers using preformed laser plasmas

Weak laser prepulses were used for the first time with picosecond-duration laser light to enhance laser-target absorption for efficient excitation of extreme-ultraviolet lasers. A traveling-wave excitation geometry and a self-healing mercury-wetted target were used with 300-ps prepulses to pump the photoionization Xe III laser at 109-nm wavelength. Fully saturated laser gain was demonstrated for both 32-ps and 1.4-ps pump pulses with use of only 150-mJ pulse energy: small-signal gain coefficients exceeded 2 cm−1 for on-target laser fluences of only 4 J/cm2.

Isoelectronic line intensity ratios for plasma electron temperature measurement (invited)

Strictly speaking, temperature is uniquely defined only in plasmas which are in complete thermodynamic equilibrium. In typical laser‐produced plasmas, measurement of electron temperature amounts to a parametrization of some part of the distribution of electron energies, typically inferred from the recombination continuum, or from the ratio of spectral lines that are implicitly dependent on the electron distribution. Where the plasma is highly transient, suffers appreciable opacity, or is subject to a background radiation field, the interpretation of temperature from disparate spectral lines can become untrustworthy. For these complicated plasmas, a conceptually simpler spectral line diagnostic offers great advantages. A technique has been introduced that begins with plasmas that include two elements of similar atomic number, in a known ratio, and compares isoelectronic lines from ions that differ only in their nuclear charge Z, and thus in their ionization potentials χi. Since these two have different val...

Extreme-ultraviolet laser photo-pumped by a self-healing Hg target

A self-healing target has been demonstrated for synchronous photo-pumping of extreme- ultraviolet lasers. The threaded, mercury-wetted copper rod, rotating in a pool of mercury, offers similar photoionization efficiency as gold targets, but without target-surface degradation. A gain coefficient of 1.4 cm-1 was obtained with mercury for the 1089 angstrom Xe2+ laser at a pump-laser intensity of 140 GW(DOT)cm-2, comparing favorably with results from gold targets.

A practical self‐healing mercury target for efficient generation of soft x‐ray radiation

We have developed a self‐healing mercury‐wetted target as a practical source of soft x‐ray radiation for photoexciting extreme ultraviolet lasers. A threaded rod, rotating in a pool of mercury, demonstrates a soft x‐ray conversion efficiency similar to that of expendable gold‐coated targets in synchronous photopumping of a photoionization Xe2+ laser at 109 nm. Surfaces self‐heal or are continuously regenerated by rewetting, while mercury debris is removed by evaporation from the target chamber walls and optics. Long target lifetime and self‐cleaning performance of the new target system are attractive features in future high‐repetition‐rate, high‐throughput applications for photopumping of extreme ultraviolet or soft x‐ray lasers, and more generally as incoherent sources for soft x‐ray lithography and spectroscopy.

Pulse distortion induced by stimulated brillouin scattering in high power double-clad Er/sup 3+//Yb/sup 3+/ doped fiber amplifier

Evidence of cascaded-Stokes waves generation due to SBS in a high power Er/sup 3+//Yb/sup 3+/ fiber amplifier is reported. Up to 40W peak power pulses have been obtained in counter-pumping configuration. This has been theoretically modeled using a coupled-waves SBS process model.

Theory and experiment in ultraintense laser-matter interaction in nanostructured Ni-nanowire targets

Nickel nanowires present >90% absorption in an effective skin-depth ~1 mum, making efficient X-ray converters. We present new theoretical and experimental results for intensities from small-signal up to very clean relativistic pulses.

40 kW sub-picosecond pulse generation using cladding-pumped Er/sup 3+//Yb/sup 3+/ fibers

Sub-picosecond pulse amplification at 1.55 /spl mu/m in a cladding-pumped Er/sup 3+//Yb/sup 3+/ co-doped fiber amplifier is studied. A peak power higher than 40 kW is obtained using a chirped pulse amplification technique. Theoretical and experimental results indicate that nonlinear pulse distortions ultimately limit the maximum achievable peak power.

Laser/plasma studies using the terawatt FCM-CPA laser at Toronto

The ratio of isoelectronic lines was used to measure the electron temperature of subnanosecond and picosecond plasmas of a range of two-element materials: NaF, Mg-Al alloy, and KCl. Modelling shows that although populations may be far from steady-state in picosecond plasmas, the ratio of isoelectronic lines may be nearly steady-state, simplifying interpretation. Contour plots of the ratios of a number of isoelectronic helium-like line-pairs, suitable for steady-state electron-temperature interpretation, are provided.

High-contrast terawatt pulses from fiberless chirped-pulse amplification laser based on 1-ps direct feedback controlled Nd:glass oscillator

A fiberless 1-TW all-Nd:glass chirped-pulse amplification laser system is described in this paper. Starting from high-contrast 1-ps pulses produced directly from a Nd:glass feedback- controlled oscillator, this system employs a fiberless, gratings-only expansion/compression scheme, and produces clean (5 X 107 prepulse contrast) 1-J, 1.2-ps recompressed pulses without added pulse-cleaning. The same system can also be configured to produce up to 5-J uncompressed 410-ps pulses. A novel subpicosecond cross-correlation technique is also described.