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A study on the pulse generation characteristics in alkali vapor and fiber lasers

  • 류시헌 (Siheon Ryu, 아주대학교 일반대학원)

초록/요약

Pulse lasers are essential light sources not only for industrial applications such as optical communications, materials processing, and bio-imaging, but also for fundamental studies in nonlinear optics. Among various platforms, diode-pumped alkali laser (DPAL) and fiber lasers have attracted significant attention as promising candidates for high-power, high-efficiency pulsed sources. DPAL inherits the advantages of gas laser, including relaxed thermal issues, weak nonlinearities, and, owing to the properties of alkali atoms, a high quantum efficiency exceeding 95%, making them well suited for power scaling. Fiber lasers also offer excellent heat dissipation, high gain, and good beam quality, and are therefore widely used for high- power operation. In this thesis, we develop and characterize pulsed lasers based on both DPAL and fiber-laser platforms. For the DPAL system, first we numerically and experimentally investigate how parameters such as beam intensity, cell temperature and buffer-gas pressure affect the output characteristics of an alkali vapor amplifier. Subsequently, coupling the alkali gain medium with a fiber resonator, we demonstrate a pulsed- mode DPAL and obtain pulses with a minimum pulse width of 123 ns at repetition rates up to 3.4 MHz (Chapter 2). On the fiber-laser platform, we construct a passively mode-locked erbium-doped fiber laser employing a carbon-nanotube saturable absorber (CNT-SA) formed by spin-coating a CNT film onto a side-polished fiber. We characterize the linear and nonlinear optical properties of the CNT-SA and demonstrate that the pulse duration of the mode-locked laser can be tuned by the external refractive index, observing a change in pulse width from 891 fs to 494 fs (Chapter 3). In summary, we demonstrated nanosecond and femtosecond pulsed lasers on DPAL and fiber-laser platforms, respectively, and systematically investigated their pulse-generation characteristics. The approaches presented here are expected to be useful for the development of high-power, high-efficiency pulsed laser sources for a wide range of applications.

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목차

1. Introduction 1
2. Diode pumped alkali laser 3
2.1 Introduction 3
2.2 Alkali gain medium 4
2.3 Alkali optical amplifier 5
2.3.1 Numerical simulation of alkali optical amplifier 5
2.3.2 Optical amplification characteristics with buffer gas pressure 6
2.3.2.1 Fabrication of cesium cell 7
2.3.2.2 Experimental and numerical simulation results 8
2.3.3 Optical amplification characteristics with incident beam size and temperature 10
2.3.3.1 Experimental results 11
2.3.3.2 Numerical simulation results 16
2.4 Pulse-mode operation of a DPAL combining a fiber ring cavity 18
2.4.1 Stimulated Brillouin scattering in fiber 19
2.4.2 Operation principle of pulse-mode DPAL 20
2.4.3 Experimental setup 21
2.4.4 Stokes waves and pump beam modulation in fiber ring cavity 22
2.4.5 Pulse-mode DPAL 25
2.5 Summary 28
3. Mode-locked optical fiber laser 30
3.1 Introduction 30
3.2 Background 31
3.2.1 Principle of passive mode-locking 31
3.2.2 CNT Saturable absorber 32
3.3 Fabrication of CNT-SA 33
3.4 Optical properties of CNT-SA 35
3.5 Experimental results 37
3.6 Summary 40
4. Conclusion 41
References 43
국문요약 48
List of Publications 49

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