Femtosecond coherent pulses in the keV range from inner-shell transitions pumped by a betatron source

Abstract

International audienceWe present a new method to generate ultra-short X-ray laser pulses by using the recently demonstrated laser-driven betatron source to photo-pump inner-shell transitions. The proposed compact set-up will then open the route to a wide range of applications. The betatron spectrum and ion-population kinetics are modeled and the temporal evolution of the gain coefficient for the K-α transitions is assessed. Using measured values of divergence, duration, and number of photons per pulse of the betatron source as input parameters, local gain values close to 60 cm^−1 are calculated for nitrogen at 3.2 nm. Significant gain values are also numerically obtained at shorter wavelengths (for neon at 1.5 nm) when the betatron energy distribution is optimized as suggested by recent laser wakefield electron acceleration experiments

Transient-gain photoionization x-ray laser

“…The photoionization inner-shell x-ray laser scheme was originally proposed by Duguay and Rentzepis [3], and since then, several possible targets and pumping schemes were studied in theory [9][10][11][12][13][14][15][16]. Although experimental attempts have been made and an inner-shell laser was demonstrated in the blue spectral domain [17] in 1983 and in the EUV region by Auger-decay pumping [18], the development of powerful XFELs [19][20][21][22][23] was needed to demonstrate this scheme in the soft x-ray spectral region at 1.45-nm wavelength by a laboratory-based experiment [1].…”

Pump requirements for betatron-generated femtosecond X-ray laser at saturation from inner-shell transitions

“…In a previous work [14], we have shown that the nitrogen density has a strong influence on the local gain value. More precisely, the peak gain value scales linearly with the gas density for pulse durations shorter than 20 fs.…”

“…Details of the atomic models for nitrogen and neon are given elsewhere [14]. Therefore only a brief description is given here.…”

“…In a previous paper [14], we proposed a new experimental approach to photo-pump inner-shell transitions by focusing a laser-based betatron radiation source in nitrogen or neon gas jets. We showed that significant gain values for the K-α transitions of both elements may be obtained by using quite a simple experimental configuration.…”

Inner-shell photo-ionisation x-ray lasing

“…∼ 6 m at the speed of light) [3] which prevents from demonstrating the lasing scheme. In order to overcome these problems, the possibility of using betatron radiation, as produced by a laser-driven relativistic electron beam, and longitudinal pumping have been recently proposed (figure 3) [4,5]. …”