Electron energy distribution in the photodetachment ofH−by two radiation fields

Abstract

We report on the energy distribution of the electrons emitted in two-color photodetachment of H in a highly nonlinear regime, and compare these results with the ones found by averaging the cross section obtained in the presence of a static field over the values taken by the low-frequency field in a cycle. Similarities and differences are discussed. PACS number{s): 32.80.RmOver the last few years, multiphoton detachment of negative ions has become a topic of both theoretical and experimenta. investigation. The main reason for carryi'ng out experiments with these systems arises from the short-range nature of the interaction between the atomic core and the outer electron that allows a clearer determination of the continuum threshold as compared to the one measured in analogous experiments where use is made of neutral atoms. This circumstance has stimulated experiments aimed at measuring the detachment threshold shift due to the presence of a strong radiation field. For this purpose experiments of detachment of negative chlorine ions by a weak field of frequency coH in the presence of a strong microwave or infrared field of frequency co'I have been carried out [1]. In these experiments the role of the intense low-frequency field (LF) of amplitude I'L was to provide the ponderomotive shift b =FL l4mcol (with m the electron mass), while the intensity of the higher-frequency field (HF) was so weak that only one HF photon was absorbed in the photodetachment process. Experimental results were obtained in two different physical regimes characterized by the ratio 6/coL, for co~in the region of uv frequencies and col in the range of infrared or microwave frequencies. In the regime characterized by 6/cuL ))1 it was not possible to make any connection between the threshold shift and the measured cross section [1,2]. The ripples found in the curve showing the cross section as a function of AH were interpreted [1 -3] in terms of interference of the direct photoelectron wave and the wave that rejects from the repulsive barrier formed by the LF field whose characteristic height was evaluated [3] to be 2b" in analogy with the explanation given in Ref. [4], where the photodetachment in the presence of a static electric field was studied. Moreover, the poor sensitivity of the photodetachment event to the variation of coL was considered as a manifestation of the quasistaticity of the process. The cross sections were in fact proved to have a behavior quite similar to the ones obtained by averaging the cross sections of photodetachment in a static electric field over the values taken by the LF field in a period [2]. The present paper is aimed at further comparing the photodetachment process of H occurring in the presence of a static field with the one in an oscillating intense field, taking the latter as linearly polarized along the direction of the HF field and where T"(q,XI )= f da f"(a)M(q, KI (a)), (2) f"(a) = exp in a+i A+i sin, a 2~L (3) (q, I g(a))=&e ' IF~rliip(r)) (4) FI q sino, FLcosu Aq =, ICL(a) = COL COL (5)q=qp+qT is the a...

Theory of the photoelectric effect assisted by an elliptically polarized laser field

“…Han [32] studied such a two-frequency ionization in the hydrogen atom by solving the Schrödinger equation numerically in momentum space. Bivona et al [33] studied the two-frequency photodetachment in H − and compared their result with the detachment in the presence of a static field. Buth et al [34,35] studied the x-ray absorption by dressed atoms using an ab initio approach.…”

Photodetachment microscopy in time-dependent fields

“…Similar studies with neutral atoms [16][17][18][19][20][21][22] are called "photoionization microscopy". Replacing static electric fields with low-frequency, particular radiofrequency, fields adds new interesting physics [23][24][25][26] which was investigated in several recent theoretical studies [27][28][29][30][31]. Yang and Robicheaux [28] showed that time-dependent terahertz fields, in addition to the spatial interference, create also temporal interference.…”