Generation of broadband high-field terahertz radiation using two-colour microplasma

2022 Fiscal Year Research-status Report

• Project/Area Number: 21K14217
• Research Institution: Okinawa Institute of Science and Technology Graduate University
• Principal Investigator: BACON David 沖縄科学技術大学院大学, フェムト秒分光法ユニット, ポストドクトラルスカラー (90899428)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: Terahertz / Optics / Microplasma

Outline of Annual Research Achievements

This project began by constructing the experimental setup in one of the four labs of the department. This original design used 40fs pulses, shortened using a hole core fiber and recompressed using staggered mirrors, to generate a 1 colour plasma. This itself was a key aspect of the project as a short pulse is vital. While unfortunately no THz signal was observed from the plasma at this point, this was not unexpected. The experimental setup was transferred to a different lab to make space for other experimental setups.

A completely new, compact and unique design for the experiment was devised, which prevented us from having to separate the two colors required for the 2 colour plasma. The optics required for this design were purchased and an intern with limited time-domain spectroscopy experience was employed by the unit to help with the setup up. Unfortunately due to time constraint he could only stay at the university for 3 months. Despite this short time, he did manage to achieve the acquisition of a THz signal from a photoconductive emitter in that time, allowing us to determine time zero and ensure that the experimental setup in aligned correctly, a crucial stepping stone in the project.

Current Status of Research Progress

3: Progress in research has been slightly delayed.

Reason

The experimental setup is almost complete with each stage having been tested using a photoconductive emitter as a THz source. Despite the progress which has been made on this project, several setbacks have unfortunately slowed the progress. Firstly, the hollow core fiber required to generate our short pulses suffered a significant malfunction due to a cooling error. This was send back to the manufacturers in France which took several months to repair. Furthermore, the university went into lockdown for several months during the covid 19 pandemic, which delayed progress on the experiment, as only limited staff and researchers were permitted on campus. Furthermore, due to border closures, the pandemic restricted us from attracting further experienced researchers to the unit. Despite these set backs, the experimental setup is still being worked upon and should hopefully yield results in the future.

Strategy for Future Research Activity

With progress being relatively slow in this project, discussions have progressed to work in collaboration with a prestigious THz group at the Laboratoire de Physique de l'Ecole Normale Superieure, Paris, France. This collaboration involved the transfer of ideas and concepts to allow them to build a similar setup in Paris. This will allow them develop the setup further using our ideas with a dedicated team of students and build upon the progress we have already made. Any further progress which is achieved will then be transferred back to OIST where they will be utilized in our own setup and for further experiments.

Causes of Carryover

Due to the project progressing slower than anticipated the Kakenhi has been given a no fee 1 year long extension. As such, some of the funds has been reallocated to next years budget to continue the project. The funding for the next fiscal year will be used to purchase optics and related equipment and be used for travel to attend conferences.