Amplification of high-order harmonics in a short laser pulse by stimulated interaction

Abstract

The case is considered of a weak Gaussian harmonic pulse of frquency (2sϩ1) passed through an atomic medium collinearly with an intense Gaussian laser pulse of frequency . The harmonic beam may be amplified or deamplified according to the balance between stimulated emission and absorption. A simple analytic expression for the gain is derived in the tunneling limit of ionization. It predicts a positive ͑negative͒ gain for positive ͑negative͒ delay of the harmonic pulse with respect to the laser pump pulse. The gain may be significant and proportional to the delay for delays of a few laser periods, much shorter than the pulse envelopes. Possibilities for experimental observations are briefly discussed.

Intense laser-induced recombination: The inverse above-threshold ionization process

“…The calculated spectrum as displayed in Fig. 1 shows a radiation cutoff ͑ប max ͒ at ϳ60 eV, in very good agreement with the analytical prediction [9][10][11][12][13],…”

“…As suggested by earlier analytical studies [9][10][11][12][13], intense laser-induced recombination should generate x-ray radiation. Thus, as a first test of our procedure, we calculate the radiation spectrum by considering an initial electron wave packet with p 0 = 0.5 scattering from the model hydrogen potential in an intense ͑2 ϫ 10 14 W/cm 2 ͒ laser field ( = 800 nm; period = 2.67 fs) with a pulse duration of 50 fs.…”

“…In this paper, we consider an alternative approach by solving the full time-dependent Schrödinger equation (TDSE) for the electron-ion recombination in an ultrashort, intense laser pulse. Our TDSE solution includes in a consistent fashion all the separate processes discussed in the recent analysis [9][10][11][12][13]. Moreover, by solving the TDSE, we can examine the dynamical evolution of the recombined population and judge the importance of the intermediate states in the intense LAR processes.…”

“…In contrast to the case of weak LAR, the study of intense laser-induced multiphoton recombination of electrons and ions has only recently received attention [9][10][11][12][13], as opposed to its complementary process of ionization [14][15][16][17][18][19]. In addition, the past few years have witnessed an increasing interest in the related process of intense laser-assisted x-ray/electronatom scattering [20][21][22].…”

“…In addition, the past few years have witnessed an increasing interest in the related process of intense laser-assisted x-ray/electronatom scattering [20][21][22]. The recent studies [9][10][11][12][13] of intense LAR have focused on the radiation spectrum (i.e., x-ray generation) and employed the strong-field approximation within a Keldysh-type formulation. These pioneering studies have mostly concentrated on the process of recombination directly into the atomic ground state with the contributions from the intermediate states neglected.…”