From Event: SPIE Organic Photonics + Electronics, 2017
Laser oscillations need a combination of gain media and optical cavities. We have used as the gain media crystals of thiophene/phenylene co-oligomers (TPCOs) that are composed of inline thiophene and benzene rings, and combined them with diffraction gratings acting as the optical cavities. We have fabricated these diffraction gratings on substrates as an external cavity.
Recently, we have directly engraved one-dimensional (1D) diffraction gratings on the surface of TPCO crystals by using focused ion beam (FIB) lithography. We regarded these diffraction gratings as a built-in cavity, and expected to be effective for producing narrowed emission peaks. However, the engraved parts of the crystals were quenched because the ion beam damaged the molecules. Engraving the diffraction gratings with a short period that is comparable in size to the beam spot caused weak emissions from the crystal.
In the present studies, we tried to keep wide unprocessed parts on the TPCO crystals with the FIB lithography. To this end, we fabricated diffraction gratings having a long period on the crystals. We chose one of the TPCOs that shows emission maxima at around 605 and 650 nm. We laminated vapor-phase-grown crystals on substrates. We engraved the equally-spaced 300 grooves with a period of 501 nm by precisely controlling FIB process conditions. We observed the emissions perpendicular to the grating grooves as well as parallel to the crystal surface under ultraviolet light illumination from a mercury lamp. We succeeded in observing a narrowed peak at 662 nm with the crystal with the 1D diffraction grating.
Takeshi Yamao, "Organic crystals with long-period diffraction gratings engraved directly on their surfaces by focused ion beam lithography (Conference Presentation)," Proc. SPIE 10360, Light Manipulating Organic Materials and Devices IV, 103600F (Presented at SPIE Organic Photonics + Electronics: August 06, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2275536.5581131885001.
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