Explosive supersaturated amplification on 3d→2p Xe(L) hollow atom transitions at λ ∼ 2.7−2.9 Å

Abstract

The Xe(L) system at λ ∼ 2.9 Å uniformly exhibits all of the canonical attributes of a strongly saturated amplifier on the full ensemble of single-vacancy Xeq+ transition arrays (q = 31, 32, 34, 35, 36) that exhibit gain. The key observables are (1) sharp spectral narrowing, (2) the detection of a narrow directed beam (δθx≅200 µrad), (3) an increase in the amplitude of the emission and the development of an intense output (⩾106 enhancement) and (4) the observation of deep spectral hole-burning on the inhomogeneously broadened spontaneous emission profile. Experimentally determined by two methods, (a) line narrowing and (b) signal enhancement, the observations for several single-vacancy 3d→2p transitions indicate a range of values for the effective small signal (linear) gain constant given by go≅25−100 cm−1. Quantitative analysis shows that this result stands in clear conflict with the corresponding upper bound go≅40−80 cm−1 that is based on available spectroscopic data and estimated with conventional theory. Overall, the observed values deviate substantially from expectations scaled to the spectral density of the measured Xe(L) spontaneous emission profile; they are systematically too high. The most extreme example is the heavily saturated Xe32+ transition at λ = 2.71 Å, a case that fails to reconcile the lower bound of the measured signal strength with the corresponding theoretically predicted maximal value; the former falls above the latter by a factor exceeding 400 giving an enormous gap. Moreover, although saturation is a prominent characteristic of the amplification at λ≅2.71 Å, as demonstrated by spectral hole-burning, the theoretical upper bound of go given for this transition is far too small for saturation to be reached. The Xe31+ transition at λ≅2.93 Å exhibits comparably pronounced anomalous behaviour. This double paradox is resolved with the Ansatz that the amplification is governed principally by the saturated gain gs, not the conventionally described small signal value go. This interpretation is further supported by the observation of deep spectral hole-burning, the signature of strong saturation, that occurs uniformly across the spectrum of the spontaneous emission profile. The effective amplification exhibits an anomalously weak dependence on the spectral density; saturation is the rule, not the exception. A lucid manifestation of the saturation is the recording of spectrally resolved x-ray yields on the Xe31+ array that are sufficiently high to produce gross structural damage to the material in the film plane of the spectrograph. The behaviour of the amplifier can be best described as an explosive supersaturated amplification. The source of this exceptionally strong amplification can be traced to the dynamically enhanced radiative response of the excited Xe hollow atom states located in the clusters that are mode coupled to the plasma waveguide forming the amplifying channel.

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

“…The Xe(L) x-ray laser at λ ∼ 2.9 Å has well documented properties [1][2][3][4][5][6]. This advance in coherent x-ray source development was made possible by the ability to controllably compress power to robust values that fall at or above the highest thermonuclear range (∼10 20 W cm −3 ).…”

Rewriting the rules governing high intensity interactions of light with matter

“…In the extended region (Z > -1 mm), the Xe(L) signal exhibits strong modulation with features of ~ 100 μm in width, a characteristic that contrasts significantly with the Xe(M) signal that shows perceptible, but far weaker modulation, even though the spatial resolution is approximately two-fold greater; the conclusion that the Xe(L) modulations are considerably sharper and more pronounced than those illustrated by the Xe(M ) counterpart follows. showing the canonical Xe(L) hollow atom spontaneous emission spectrum produced from Xe clusters with 248 nm excitation whose properties are known from earlier studies [38,61,62]. (a) Xe(L) spectrum recorded at point B in Fig.5(b).…”

“…In addition, the direct hollow atom production [34] was a huge bonus, since it eliminated the need for the relatively slow process of recombination to form the excited Xe*(L) states. Hence, excited levels exhibiting prompt x-ray emission were efficiently produced, an outcome that automatically produced inverted population densities and subsequently enabled amplification in the multikilovolt x-ray spectral region 4.5 keV on 3d  2p transitions to be achieved [38,39,[61][62][63]84]. Recent work [85] has extended these findings with the demonstration of amplification on the Kr(L) 3s  2p Kr 26+ 1…”

“…All of the states producing the spectrum shown in Fig. (26) possess a 2p-vacancy and a fraction of the emission in the blue wings of both lobes arises from 2s2p double vacancy levels [39,[61][62][63]66].…”

“…that defines the peak electric field E for the onset of relativistic motions for elections with mass m and charge e driven at angular frequency ω, (b) the vacuum pair creation limit, the upper value bounding the achievable intensity that is associated with ultrarelativistic electron/positron cascades [97], (c) the intensity I  4.6 × 10 29 W/cm 2 corresponding to the Schwinger/Heisenberg limit [98,99], and (d) the point characterizing the intensity of saturated amplification with the Xe(L) hollow atom system [38,39,[61][62][63][64][65][66].…”