Diamond has arisen as a much-sought out topic of research due to its excellent mechanical, chemical, electrical, optical, and thermal properties. Nanodiamonds or diamond nanoparticles has recently generated significant interest as a key material for lasers, biophotonics, and quantum optical applications. Low toxicity, excellent bioconjugation, superior biocompatibility, and simplicity of manufacturing are among other properties that make NDs superior compared to other materials such as metallic nanoparticles, quantum dots or dye molecules. Higher Raman cross section and superior thermo-optical properties of diamond have triggered interests for Raman laser developments. In this context, I studied and investigated the spectroscopic, linear, and nonlinear optical properties of ND particles in different concentrations, average sizes, and samples in combination with gold nanoparticles to further determine a deeper understanding on how to engineer nanodiamonds to enhance their optical/biophotonic applications.

Chapter 1 introduces diamond as a whole and explicitly shows its various properties and capabilities. Diamond is an intricate network of carbon atoms and is considered a superior choice of nanoparticles primarily due to its intrinsic properties, including: low toxicity, excellent bioconjugation, superior biocompatibility, high Raman gain, broad transmission spectrum, simplicity of manufacturing, and superior hardness. Nanodiamonds inherit most of the superior properties of bulk diamond and deliver them at the nanoscale. An interest in nanodiamond research applications has been increasing due its unique properties such as bright and non-bleaching fluorescence, biocompatibility, and flexibility for surface modification. Understanding how diamond is synthesized, prepared, and how their color defects are also synthesized is discussed, as well as its applications in biophotonics, magnetometry, quantum information processing, and laser physics.

Chapter 2 explores the absorption and Raman spectroscopic properties of nanodiamonds. Absorption spectra of ND solutions are obtained by preparing NDs in solvents with different concentrations. Absorbance of ND solution at a specific wavelength has been measured and plotted as a function of ND concentration to determine the detection limit for lowest concentration. This data can be used as a calibration curve for measuring the unknown concentration of the NDs in a solution when they are used as biomarkers in assays. Raman spectroscopy has also been used to characterize the ND surface. Raman signals in various ND samples are found to be affected by graphite or carbon-based contaminants deposited on the ND surface.

Chapter 3 takes a step further on determining the actual value of absorption in ND solutions. Accurate measurement of absorbance or extinction of ND particles is important for biophotonic applications. Traditional spectrophotometry described in the previous chapter could not provide an accurate measurement of absorbance (or extinction) in ND solutions in the presence of losses due to scattering, fluorescence and heating. In many applications, it is necessary to quantify absorption and scattering yields of ND particles independently. In this chapter, photothermal spectroscopy (PTS) has been used to determine absorption and scattering yields of ND particles. Photothermal measurements provide real estimation of absorption and scattering yields in ND solutions which could not be inferred from previous spectrophotometric measurements. PTS measurements show the advantage over traditional transmission-based spectrophotometry in determining the absorption yield of ND particles irrespective of scattering. A pump-probe photothermal Z-scan experiment has been conducted to determine thermal extinction and scattering extinction of ND particles of sizes between 10 -- 150 nm at 445nm and 532nm wavelengths. Results show thermal extinction measured from PT experiment grows in proportion to the volume of the particle while the scattering extinction grows in proportion to the square of the volume of the particle showing agreement with the Rayleigh scattering.

Chapter 4 reveals the importance of studying the nonlinear optical (NLO) response of nanodiamond as it has not been very well studied. Third-order nonlinear optical effects form the physical basis for many applications in high-speed optical communication networks. In this context, investigations of third-order nonlinearity in diamond samples at nanoscale are highly relevant. In this chapter, third-order NLO responses of NDs and ND/Au hybrids are investigated using a near-IR nanosecond pulsed laser source. In particular, this chapter discusses the efforts to measure nonlinear absorption and refraction in ND solutions formed in DI water and DMF using a 1064nm pulsed laser. A single-beam Z-scan technique has been used to determine the values of nonlinear refractive index, n2 and nonlinear absorption coefficient, beta. Optical limiting behavior of NDs has also been investigated using pulsed excitation. (Abstract shortened by ProQuest.).