ORCID

0000-0002-3446-7608

Keywords

Mid-infrared; Nonlinear frequency conversion; Quasi-phase matching; Optical parametric oscillator; Nonlinear absorption

Abstract

Mid-infrared (MIR) spectral region represents a vital part of the electromagnetic spectrum, offering applications in spectroscopy, biomedicine, and remote sensing. However, there are no direct broadband MIR laser sources. Nonlinear frequency conversion techniques using second-order nonlinear materials, such as optical parametric oscillator (OPO) and intra-pulse difference frequency generator (IDFG), are promising methods for generating a broadband MIR spectrum. To achieve an efficient conversion, the phase matching condition between the interacting waves of the nonlinear process must be satisfied. Quasi-phase matching (QPM) is a special technique that enables efficient nonlinear processes in materials that cannot be conventionally phase matched using birefringence. In addition, the use of an ultra-fast laser to achieve a high peak intensity begets supplementary higher-order nonlinear processes, such as multiphoton absorption and nonlinear refraction, which must be considered. In this dissertation, QPM materials made by stacking periodically inverted 2D nonlinear GaSe crystals, were studied in different frequency conversion schemes: 4.7->2.35 µm, 2.35->1.175 µm second harmonic generation (SHG), and 2.35->4.7 µm OPO. The first two processes based on the QPM GaSe demonstrate good performance, close to the QPM theoretical limit. However, the OPO, which is the reverse process of the first SHG process, operates on a third-order nonlinearity instead of the intended second-order. Lastly, for the first time, seven semiconductors were characterized in the z-scan technique in the femtosecond regime using long-wave infrared (LWIR) 7-12 µm pulses, produced by IDFG. Multiphoton absorption (MPA) has been shown in narrow bandgap materials, InAs and Ge, while saturable absorption has been demonstrated in Si, GaAs, ZnSe, GaSe and GaP in an open aperture z-scan. Closed aperture z-scan manifests nonlinear refraction and cumulative nonlinearity, which takes place when the pulse period is much shorter than the decay time of the carriers.

Completion Date

2026

Semester

Spring

Committee Chair

Vodopyanov, Konstantin

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Electrical engineering

Format

PDF

Document Type

Dissertation

Identifier

DP0053237

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