Coherent near-field detection system based on free electron excitation and photoelectric detection

Abstract

The invention discloses a coherent near-field detection system based on free electron excitation and photoelectric detection, and belongs to the crossing field of vacuum electronics and terahertz photoelectric detection technologies. A femtosecond laser source is adopted to generate femtosecond laser, the femtosecond laser is divided into two beams by a beam splitter, one beam excites a photocathode to generate a pulsed electron beam, the pulsed electron beam excites a surface wave of a to-be-measured material, and a photoconductive antenna composed of a substrate and a metal electrode is placed on the lower surface of the to-be-measured material (if the to-be-measured material is a metal grating; if not, two adjacent gratings are used as metal electrodes) to directly sense the surface wave of the to-be-measured material; and the other beam of femtosecond laser is injected into the photoconductive antenna through the time-delay light path, so that photoelectric sampling is realized, and the detection of the surface wave of the to-be-measured material is completed. According to the method, the influence of the needle tip on the near-field signal is avoided, the intensity of the electron projection field on the surface of the object is far less than that of the surface wave, and the time domain direct detection of the relatively pure near-field signal can be realized.

Description

technical field [0001] The invention belongs to the intersecting field of vacuum electronics and terahertz photoelectric detection technology, and relates to a photocathode photoelectron emission and a time-domain detection method of a photoconductive antenna. Background technique [0002] Photocathode electron emission, together with thermal electron emission, field electron emission, and secondary electron emission, constitutes four basic forms of electron emission; in the process of photocathode electron emission, the electrons inside the cathode material absorb the laser photon energy , produce an energy level transition and leave the surface of the material, and finally complete electron emission, and the emission period is consistent with the pulse laser repetition period. [0003] Photoconductive antennas are terahertz generation or detection devices based on semiconductors (commonly used materials are gallium arsenide and sapphire silicon wafers) and bimetallic anten...

AI Technical Summary

Problems solved by technology

However, this type of near-field system has certain defects in detecting the near-field on the surface of materials or structures. For example, both excitation and detection come from the probe, so the spatial phase of the surface near-field cannot be directly seen; and the resolution of the system depends on the probe. , not only is it difficult to further improve, but also there is a contradiction between near-field coupling efficiency and imaging resolution

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