| The development of attosecond pulse technology provided a powerful technical support for studying ultrafast electronic process and observingã€controlling and tracing of electronic dynamic process in the scale of atoms and molecules, It has promoted the microscopic physical and chemical, biological research, Therefore, In the past ten years scientists have been devoted to the study of such.. Up to now, atom in strong laser field emission harmonics due to its wide spectral range, good continuity, so it has become the main source of gaining attosecond pulses. At present, the laboratory is mainly the high-order harmonic generation in strong laser field using inert gas to obtain the attosecond pulse. currently,the methods to gain a single attosecond pulse including polarization gate technology, two-color, three color laser, laser and semi periodic field as well as in the chirped laser and electrostatic field driven atomic to obtain a single attosecond pulse.The following is our main work: In our work,,the theory method we have used is the strong field approximation method,in short we call it SFA.in addition,we also employ polarization gate above mentioned,under the polarization gate helium atom can emit the high-order harmonic generation(HHG) when exposed to a two-coloure midinfrared combined field with the wavelength are respectively 2128 nm and 1064 nm. Research indicates that, under this combination field, helium atom can produce a high harmonic that cut-off is so high and near the cutoff position there appeared supercontinuum spectrum, superposing the some rang of that, an isolated 44.5as pulse is generated. In order to clearly understand the generation mechanism of the attosecond second pulse, we also make the time-frequency analysis of the high-order harmonic generation. Our results shows that it is because of the polarization gate, emission of pulse outside the gate is suppressed outside the gate,hence it can produce a isolated attosecond pulse. |
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