研究目的
To develop a new THz source capable of generating intense sub-cycle pulses with tunable elliptical polarization, addressing the challenge of controlling polarization states in high-field THz applications.
研究成果
The study successfully demonstrates the generation of intense THz pulses with up to 70 kV/cm electric field and tunable elliptical polarization from linear to quasi-circular, achieved through a phase mask-induced time delay in an ILAPCA. This source is advantageous for nonlinear applications due to collinear and overlapping pulses, and it addresses the need for polarization control in THz photonics, particularly for sub-cycle phenomena.
研究不足
The polarization state is tunable but exists only over a sub-cycle time scale, limiting its duration. The use of quasi-half-cycle pulses may affect polarization quality; switching to quasi-single cycle pulses with a binary phase mask could improve this. The bias field applied was limited to 28 kV/cm, whereas higher fields could enhance THz intensity but were not utilized in this study.
1：Experimental Design and Method Selection:
The experiment uses an interdigitated large aperture photoconductive antenna (ILAPCA) with vertical and horizontal electrodes to generate THz pulses with crossed polarizations. A phase mask (quartz window) is applied to introduce a time delay between polarizations, enabling tunable elliptical polarization.
2：Sample Selection and Data Sources:
The ILAPCA is fabricated on a polycrystalline ZnSe substrate with Au/Cr electrodes, using photolithography. Delay masks of varying thicknesses (
3：12, 2, 25, 1 mm) are used to modulate the time delay. List of Experimental Equipment and Materials:
Equipment includes a 400 nm laser for pumping, off-axis parabolic mirrors for focusing and collimating THz radiation, a wire grid polarizer for polarization filtering, a GaP crystal for electro-optic detection, and photodiodes for measurement. Materials include ZnSe substrate, Au/Cr electrodes, quartz masks.
4：Experimental Procedures and Operational Workflow:
The ILAPCA is pumped with a 400 nm laser beam at 15 mJ energy and biased at 28 kV/cm. THz pulses are generated, focused, and detected using electro-optic techniques with polarization analysis. Different mask thicknesses are tested to vary the time delay and polarization state.
5：Data Analysis Methods:
Temporal waveforms of THz electric fields are measured, and polarization states are analyzed based on projections and delays between P- and S-polarized components, using standard electro-optic detection methods.
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