Ervin Racz

Realization of the conceptual ideal for x-ray amplification

The Xe(L) system is an amplifier with fundamentally different dynamic characteristics from all previously developed laser amplifiers; it represents the conceptual ideal through full utilization of the Kramers–Kronig relations that fundamentally couple the dispersive and absorptive components. The dispersive response of the system, through optimal governance of the power compression, rules the amplification and establishes a minimum gain for the amplifier. Accordingly, the amplification requires a minimum value of the dispersion to be surpassed; the corresponding gain follows automatically. As a leading consequence, since this minimum gain is sufficiently high, the key experimental observation is the uniform presence of saturated amplification signaled by strong spectral hole burning on all transitions exhibiting amplification, including double-vacancy lines. This cardinal signature demonstrates that the amplification is legislated by the saturated gain gs, not the corresponding small signal value g0. The chief outcome is that explosive dispersion yields perforce explosive amplification and the efficient generation of maximally bright coherent power.

Temperature enhancement of Xe(L) x-ray amplifier (λ ∼ 2.9 Å) emission

Cooling of the xenon nozzle flow to T = 230 K produces three leading effects. They are (1) a ~2.5-fold enhancement of the Xe(L) hollow atom emission on the single-vacancy 3d ? 2p charge state arrays, (2) the production of amplifying self-trapped plasma channels with significantly enhanced lengths and (3) very sharply augmented emission on () Xe(L) double-vacancy transitions in the ? 2.80 ? region.

Power scaling of the Xe(L) amplifier at λ~ 2.8 Å into the petawatt regime

Single-pulse and time-integrated spectral measurements of the characteristics of the Xe(L) amplifier at λ ~ 2.8 A indicate an efficiency of energy extraction of ~30% over a bandwidth of ~500 eV. These observations, together with data from prior studies, provide a basis for estimating a corresponding set of scaling limits for a laboratory sized ~4.5 keV Xe(L) system. Specifically, they are a peak power Px ~ 6.0 PW, an unfocused peak intensity Ix ~ 3.4 × 1021 W cm−2, peak brightness figures corresponding to B ~ 4.1 × 1034 photons s−1 mm−2 mrad−2 (0.1% bandwidth)−1 and Px/λ2 ~ 7.6 × 1030 W cm−2 sr−1, and an x-ray pulse length τx ~ 5–10 as.

Spatially resolved observation of the spectral hole burning in the Xe(L) amplifier on single and double vacancy 3d → 2p transitions in the 2.62 Å < λ < 2.94 Å range

The analysis of spatially resolved Xe(L) spectra obtained with Z−λ imaging reveals two prominent findings concerning the characteristics of the x-ray amplification occurring in self-trapped plasma channels formed by the focusing of multi-TW subpicosecond 248 nm laser pulses into a high-density gaseous Xe cluster target. They are (1) strongly saturated amplification across both lobes of the Xe(L) hollow atom 3d → 2p emission profile, a breadth that spans a spectral width of ~600 eV, and (2) new evidence for the formation of x-ray spatial modes based on the signature of the transversely observed emission from the narrow trapped zone of the channel. The global characteristics of the spectral measurements, in concert with prior analyses of the strength of the amplification, indicate that the enhancement of the x-ray emission rate by intra-cluster superradiant dynamics plays a leading role in the amplification. This radiative interaction simultaneously promotes (a) a sharp boost in the effective gain, (b) the directly consequent efficient production of coherent Xe(L) x-rays from both single and double vacancy 3d → 2p transition arrays, estimated herein at ~30%, and (c) the development of a very short x-ray pulse width τx. In the limit of sufficiently strong superradiant coupling in the cluster, the system assumes a dynamically collective character and acts as a single homogeneously broadened transition whose effective radiative width approaches the full Xe(L) bandwidth, a breadth that establishes a potential lower limit of τx ~5–10 as, a value substantially less than the canonical atomic time ao/αc 24 as.

The Nuclear Epoch of Laser Interactions

The history of power compression is a series of developmental epochs that are (1) characteristically marked by a technological breakthrough and (2) generally separated by a factor of ∼1010 in power density. Based on new advances in high‐power coherent x‐ray technology, the transition to a new nuclear epoch of laser interactions is presently commencing. Chief outcomes foreseen are (1) the generation of power densities in the 1028–1030 W/cm3 realm, (2) the controlled induction of nuclear interactions, and (3) the production of new states and forms of nuclear matter.

Observation of Nonlinear Optical Coupling in the Kiloelectronvolt X-Ray Regime

Experimental findings with Xe(M) radiation in the ~1 keV X-ray region have confirmed the presence of a predicted zone of anomalously strengthened radiative coupling operative at sufficiently high intensity (I >; 1015 W/cm2) and frequency (hω >; 5 eV). These new results herald the general existence of a strongly enhanced modality of radiative interaction that is based on ordered-driven electron motions in the attosecond regime.

Stable formation of ultrahigh power-density 248 nm channels in Xe cluster targets

The optimization of relativistic and ponderomotive self-channeling of ultra-powerful 248 nm laser pulses launched in underdense plasmas with an appropriate longitudinal gradient in the electron density profile located at the initial stage of the self-channeling leads to (1) stable channel formation and (2) highly efficient power compression producing power densities in the 1019-1020 W/cm3 range. The comparison of theoretical studies with experimental results involving the correlation of (a) Thomson images of the electron density with (b) x-ray images of the channel morphology demonstrates that more than 90% of the incident 248 nm power can be trapped in stable channels and that this stable propagation can be extended to power levels significantly exceeding the critical power of the self-channeling process.

Observation of a Curve Crossing Mechanism in the Field Ionization of Inner-Shell Excited Single

Anomalous intensity dependent quenching of the Xe(L) hollow atom emission from the single Xe³³⁺(2p̅) and double Xe³⁴⁺(2s̅2p̅) vacancy 3d→2p transition arrays indicates the presence of a state-selective curve crossing mechanism for the field ionization of the excited 3d⁴ configuration by intense (2-3 × 10²⁰ × W/cm²) 248-nm radiation.

{\rm Xe}^{33+}{(2\bar{\rm p})}

Anomalous intensity dependent quenching of the Xe(L) hollow atom emission from the single Xe³³⁺(2p̅) and double Xe³⁴⁺(2s̅2p̅) vacancy 3d→2p transition arrays indicates the presence of a state-selective curve crossing mechanism for the field ionization of the excited 3d⁴ configuration by intense (2-3 × 10²⁰ × W/cm²) 248-nm radiation.

and Double

The analysis of spatially resolved Xe(L) spectra obtained with Z−λ imaging reveals two prominent findings concerning the characteristics of the x-ray amplification occurring in self-trapped plasma channels formed by the focusing of multi-TW subpicosecond 248 nm laser pulses into a high-density gaseous Xe cluster target. They are (1) strongly saturated amplification across both lobes of the Xe(L) hollow atom 3d → 2p emission profile, a breadth that spans a spectral width of ~600 eV, and (2) new evidence for the formation of x-ray spatial modes based on the signature of the transversely observed emission from the narrow trapped zone of the channel. The global characteristics of the spectral measurements, in concert with prior analyses of the strength of the amplification, indicate that the enhancement of the x-ray emission rate by intra-cluster superradiant dynamics plays a leading role in the amplification. This radiative interaction simultaneously promotes (a) a sharp boost in the effective gain, (b) the directly consequent efficient production of coherent Xe(L) x-rays from both single and double vacancy 3d → 2p transition arrays, estimated herein at ~30%, and (c) the development of a very short x-ray pulse width τx. In the limit of sufficiently strong superradiant coupling in the cluster, the system assumes a dynamically collective character and acts as a single homogeneously broadened transition whose effective radiative width approaches the full Xe(L) bandwidth, a breadth that establishes a potential lower limit of τx ~5–10 as, a value substantially less than the canonical atomic time ao/αc 24 as.