All ETDs from UAB

Advisory Committee Chair

Sergey B Mirov

Advisory Committee Members

Vladimir V Fedorov

Mary E Zvanut

Clayton E Simien

Krishen Appavoo

Document Type

Dissertation

Date of Award

2021

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

Many organic molecules exhibit strong and narrow absorption in the middle infrared (mid-IR) 2-8 μm and long-wavelength-infrared (LWIR) 8-20 μm spectral ranges. Hence, this infrared laser radiation is of interest for spectroscopy, remote sensing of atmospheric constituents, oil prospecting, as well as the number of applications such as free-space optical communication, laser surgical and dental treatment, and many defense-related applications. Transition metal (TM) doped II-VI semiconductors exhibit highly favorable spectroscopic properties for many mid-IR laser applications. Among these materials the most significant results have been obtained with the use of Fe:ZnSe crystals because of their unique properties such as broad emission and absorption bands, the absence of excited state absorption, and high energy storage capability. It was well documented in the literature that Fe:ZnSe lasers can effectively operate both at room and low temperatures. However, a lack of simple, cost-effective, and compact pump sources for Fe:ZnSe lasers limits their practical applications. The first major objective of the dissertation is to study, design, and develop a convenient pump source for Fe:ZnSe laser. Since 2.94 µm Er:YAG laser radiation nicely overlaps with the absorption band of Fe2+ ions in II-VI materials, a Q-switched Er:YAG laser is a promising pump source for the room temperature (RT) Fe:ZnSe laser. With this regards we study laser operation of home-made, spinning mirror mechanically Q-switched (MQS), flashlamp-pumped 2.94 m Er:YAG laser. The highest output energy of 805 mJ with a pulse duration of 60 ns was realized at a 1 Hz repetition rate. Using optical triggering, the pulse jitter was measured to be smaller than 10 ns for 160 ns Q-switched pulses, which could be applicable to many laser applications where precise synchronization of pulses is required. Although many spectroscopic characteristics of Fe:ZnSe crystals have been well documented, there are still some important spectroscopic characteristics that require additional studies. Among them is counterintuitive dependence of the Fe:ZnSe luminescence lifetime with temperature below 100 K and unusual amplification behavior of highly doped Fe:ZnSe gain media hampered by amplified spontaneous emission processes. These processes significantly limit the energy storage capability and output characteristics of Fe:ZnSe lasers and amplifiers. One of the objectives of this work is to understand the unclear physics behind these effects in order to optimize the amplification performance of Fe:ZnSe gain media. While an effective way to fabricate Fe:ZnSe gain element is post-growth thermal diffusion, a relatively small diffusion rate of Fe in ZnSe crystals, hampers fabrication of large size, homogenously doped Fe:ZnSe samples. The hot-pressed ceramics fabrication route has a good potential to overcome these limitations. This dissertation is also focused on comparative laser spectroscopic characterization of hot-pressed ceramic Fe:ZnSe media with polycrystalline samples fabricated by the post-growth thermal diffusion method. We report spectroscopic characterizations of hot-pressed Fe:ZnSe ceramic samples and their first RT gain-switched lasing pumped by 2.94 μm radiation of MQS Er:YAG laser operating at 3 Hz. The maximum output energy at 4.2 m was 41 mJ with 130 ns pulse duration. This technique could be attractive for the future development of high-energy short-pulse solid-state mid-IR systems. Another major objective was to design and characterize a RT 2.94 µm MQS Er:YAG laser pumped Fe:ZnSe MOPA system as a pump source for optically pumped CO2 lasers and amplifiers.

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