| Author: | Cheng, Ping Kwong |
| Title: | Study the novel group 10 TMDS materials for pulsed laser applications |
| Advisors: | Tsang, Y. H. (AP) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Two-dimensional materials Nonlinear optics -- Materials Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Physics |
| Pages: | xxvi, 164 pages : color illustrations |
| Language: | English |
| Abstract: | Pulsed lasers have attracted substantial interest due to their extensive range of applications in scientific research, industrial sectors, optical communication, eye surgery, and medicine. Recently, novel two-dimensional (2D) materials have been utilized as nonlinear optical (NLO) materials to fabricate advanced saturable absorbers (SAs) for inducing passive Q-switching and mode-locking laser operations, which is a preferable modulation device in many applications compared to the costly, complicated, and bulky active modulators. Due to their strong nonlinear properties, such as high saturable absorption and reverse saturable absorption under high-intensity light excitation, 2D materials have emerged as the next generation of SAs. Among 2D materials, platinum (Pt) and palladium (Pd) based group 10 layered transition metal dichalcogenides (TMDs) offer a new opportunity to fabricate advanced SAs for passive pulsed laser generation, as a result of their tunable energy band, broad operation wavelength regime, prominent NLO response, high charge carrier mobility, and high air stability. Therefore, this thesis focused on investigating and demonstrating the NLO property of these group 10 TMD materials for ultrafast laser generation. Firstly, the saturable absorption property of the layered platinum ditelluride (PtTe2) is investigated. By utilizing the cost-effective ultrasonic liquid-phase exfoliation (LPE) process, PtTe2-nanosheets are fabricated. The as-exfoliated PtTe2-nanosheets are then mixed into polyvinyl alcohol (PVA) polymer to form a transmission type PtTe2-PVA composite SA. This PtTe2-based SA is incorporated into the Ytterbium-doped fiber (YDF) ring cavity in order to generate Q-switched pulsed lasers, for the first time. The highest obtained single pulse energy is 74.0 nJ, corresponding to 5.2 μs pulse duration, 33.5 kHz repetition rate, and 2.48 mW average output power, which is comparable with the performance of other TMDs-based SAs. This work expresses and confirms the immense utilization potential of the group 10 Pt-based TMDs for saturable absorber applications. Secondly, NLO properties and SA performance of the Pd-based TMDs materials are analyzed. By using palladium disulfide (PdS2) material, practical PdS2-PVA, and PdS2-side polished fiber (SPF) SAs are fabricated. The Q-switched pulses are obtained by utilizing PdS2-PVA SA in the Erbium-doped fiber (EDF) cavity, with the narrowest pulse duration of 4.5 μs and highest repetition rate of 26.0 kHz. While the PdS2-SPF SA is employed for mode-locked laser generation with an ultrashort pulse duration of 375 ps and 803 fs in YDF and EDF cavities, respectively, which confirms the high performance of the fabricated evanescent field type SPF-based SAs. Following, palladium diselenide (PdSe2)-SPF SA is used to obtain a switchable laser mode operation (between Q-switched and mode-locked modes) by adjusting the intracavity polarization state in the EDF system. This switchable laser mode ability expands an opportunity for designing multi-mode lasers using a single laser system. Here, the Q-switched operation mode is attained with a broad modulation range of pulse duration from 18.5 μs to 2.0 μs and repetition rate from 16.4 kHz to 57.0 kHz. And the pulse duration of the mode-locked operation is 766 fs with time-bandwidth produce (TBP) of 0.39. Next, a detailed fabrication method of the PdTe2-SPF SAs using the aerosol jet printing (AJP) deposition technique is discussed along with the saturable absorption property of PdTe2 material. The fabricated PdTe2-SPF SAs are employed to realize broadband ultrafast laser generation with pulse durations of 170 ps, 570 fs, and 1.59 ps in YDF, EDF, and Thulium-doped fiber (TDF) cavities, respectively. Moreover, an adjustable Q-switched and high-repetition-rate (0.7 GHz) based 58th harmonic mode-locked pulses are obtained in the EDF system, which can contribute to the astronomical frequency comb and long-distance optical communication. This work of fabricating SAs using the AJP method illustrates a new SA fabrication method for optimizing the saturable absorption performance, as well as exhibits a systemic and repeatable SA manufacture processing. The signature SA parameter, modulation depth, of PdS2, PdSe2, and PdTe2-SAs are estimated as 1.7 %, 7.01 %, and 41 %, respectively, at central wavelength of 1560 nm. These results illustrate that Pd-TMDs can be used as future NLO materials for advanced ultra-fast photonics devices. Finally, the NLO performances of PdSe2 and PdTe2 TMDs are investigated by home-made Z-scan systems with mode-locked laser sources at 1 μm and 1.5 μm wavelength regimes. In order to inquire about the NLO response with different lateral sizes of samples to optimize SA fabrication, the detail of sample preparation is described. The highest nonlinear absorption coefficient (β) of PdSe2-IPA supernatants is measured as -5.00×103 and -0.28×102 cm/GW at 1066 and 1560 nm, respectively. Also, the highest β of PdTe2-IPA supernatants is realized as -8.05×103 and -0.55×103 cm/GW at 1066 and 1560 nm, respectively. Besides, the highest nonlinear refractive index (n2) of PdSe2 is estimated as -105×10-2 cm2/GW and -1.19×10-2 cm2/GW at 1066 and 1560 nm, respectively. And the n2 of PdTe2 is determined as -62×10-2 and -1.9×10-2 cm2/GW at 1066 and 1560 nm, respectively. The prominent nonlinear absorption response is found from the lower centrifuge speed of the PdSe2-IPA sample, which is comparable with other 2D materials. These works broaden and motivate the optimization of the NLO property of PdSe2 and PdTe2 materials by adjusting their morphological features, hence indicating promising optical performances, and signifying their future advanced applications. |
| Rights: | All rights reserved |
| Access: | open access |
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