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Werner, Maxwell

University of British Columbia

The field of two dimensional materials is growing rapidly, with monolayer transition metal dichalcogenides (TMD) showing promise for applications in electronics and optoelectronics. Multidimensional coherent spectroscopy (MDCS) is a nonlinear technique which offers a significant advantage over commonly used linear spectroscopy, allowing for the direct determination of homogeneous linewidths and coherent coupling between states. These capabilities also allow for identification of decoherence mechanisms. Moreover, collinear MDCS allows for hyperspectral imaging which could be leveraged to characterize and improve sample fabrication, a key concern for monolayer systems and heterostructures. Towards this end, we have developed an ultrafast light source which, when combined with a commercial MDCS system, can be utilized to study a variety of 2D semiconductors with optical bandgaps in the visible to near infrared. The light source is a synchronously pumped Optical Parametric Oscillator (OPO), capable of producing optical pulses with approximately 50nm bandwidths and a center wavelength tunable from 650nm to 900nm through adjustment of the cavity length and lithium triborate (LBO) crystal temperature. The design, characterization and operation of this OPO is presented for the benefit of future system users. Additionally, cavity simulations indicate that bandwidth limitations are ultimately imposed by the cavity mirror dispersion. Suggestions are made to overcome these limitations in the future using alternative dispersion compensation methods or single-pass nonlinear broadening. To measure multi-dimensional spectra, we utilized the MONSTR Sense Technologies BIGFOOT Ultrafast Spectrometer. Using monolayer MoSe₂ samples as a benchmark, we worked to verify the operation of the spectrometer. Two prominent artifacts were observed in the measured spectra – a narrow peak along the diagonal and a vertical stripe extending across the excitation energy axis. The source of the narrow diagonal feature was determined to be a stray retro-reflection. We were unable to definitively identify the source of the vertical feature; however, our troubleshooting efforts are catalogued, and additional considerations are presented for future testing. Despite the remaining artifact, we present a low temperature 2D spectra obtained from unencapsulated MoSe₂, with exciton and biexciton energies showing good agreement with the literature.

Text

2024-08-21

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88992

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/