Photonics Research, 2019, 7 (7): 07000742, Published Online: Jun. 17, 2019
Graphene-based saturable absorber and mode-locked laser behaviors under gamma-ray radiation 
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Fig. 1. (a) Schematic of the graphene SA with a UV-cured polymer over-cladding on the monolayer graphene sheet and (b) back-gated graphene FET including the over-cladding. (c) Optical microscope image of the graphene SA at the edge of interaction region. (d) Photo of the devices.
Fig. 2. (a) NLT of the graphene SA measured by the femtosecond pulses in TE mode (inset: NLT in TM mode). (b) PDL and IL of the graphene SA as a function of irradiation dose measured by the CW light. (i) 0 kGy, (ii) 2.5 kGy, (iii) 4.8 kGy, and (iv) 6.7 kGy at 98 Gy/hr average dose rate. Note that the 6.7 kGy-irradiated sample (iv) was measured three days after radiation (without any special treatment), showing the recovery property in PDL.
Fig. 3. Measured NLT curve of the graphene SA in TE mode (i) before radiation and (ii) three days after radiation of 6.7 kGy (inset: NLT curve in TM mode). Note that there was no special treatment for three days.
Fig. 4. Measured transfer characteristics of the back-gated graphene FET including the over-cladding layer. The results are for (i) 0 kGy, (ii) 2.3 kGy, and (iii) 4.2 kGy at a 95 Gy/hr dose rate [inset: changes of the average charge carriers mobility [(iv) electron and (v) hole] and (vi) the Dirac voltage of the graphene FET as a function of irradiation dose]. Note that the result of 4.2 kGy irradiation (iii) was measured four days after radiation without any special treatment.
Fig. 5. Measured Raman spectra of our sample under different radiation conditions (0 kGy, 2.1 kGy, and 4.2 kGy).
Fig. 6. (a) Photo of the radiation test setup of the mode-locked laser. Note that the rest of the parts in the laser except the graphene SA were irradiated with a lower dose (3.4% of the irradiation dose to the graphene SA). (b) Schematic of the laser under test. EDF, Er-doped fiber; LD, pump laser diode; PC, polarization controller.
Fig. 7. (a) Optical spectra and (b) time-domain photodetected pulse trains of the mode-locked laser for different radiation conditions (0 kGy, 0.5 kGy, 1.0 kGy, 1.5 kGy, and 1.98 kGy). (c) Average optical power change of the mode-locked laser while the graphene SA was irradiated at a 45 Gy/hr dose rate.
Dohyun Kim, Nam Hun Park, Hyunju Lee, Jaegoan Lee, Dong-Il Yeom, Jungwon Kim. Graphene-based saturable absorber and mode-locked laser behaviors under gamma-ray radiation[J]. Photonics Research, 2019, 7(7): 07000742.
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