Highly coherent diode lasers: Noise, frequency stabilization, and linewidth reduction

This dissertation addresses a study on noise and frequency control of diode lasers. Issues addressed include atomic frequency references for diode laser stabilization, frequency stabilization to the atomic frequency references, and linewidth reduction with negative electrical feedback. This study is important for the application of diode lasers to WDM (Wavelength Division Multiplexed) or FDM (Frequency Division Multiplexed) based coherent optical communications, precise laser spectroscopy, and coherent optical measurements.; The absorption spectra associated with D{dollar}sb2{dollar}-lines of rubidium are studied for use as frequency references. The Zeeman absorption lines between the 5P{dollar}sb{lcub}3/2{rcub}{dollar} excited and the 5S{dollar}sb{lcub}1/2{rcub}{dollar} ground states are calculated numerically and measured experimentally for magnetic fields up to 1000 Gauss. From the saturated Zeeman absorption spectrum obtained with linearly polarized light, we report a new Doppler-free frequency reference. With circularly polarized light, we report tunable Doppler-free frequency references with 3 GHz tuning ranges within the magnetic field of 1000 Gauss.; We engineer a stable tunable diode laser by locking to a D{dollar}sb2{dollar} absorption line of Rb. The hyperfine Zeeman absorption spectrum utilized includes the new Doppler-free absorption spectra and the tunable frequency references. The range of applied longitudinal magnetic fields extends up to 1000 Gauss. With the new Doppler-free absorption spectra, a highly stable diode laser is obtained using Zeeman modulation. With the linear absorption spectra 3 GHz of frequency tuning is obtained.; We study frequency and intensity noise and the laser bandwidth spectrum of the diode laser. This study is important to reduce noise with negative electrical feedback. We map out the frequency and laser bandwidth spectra less than 1 GHz and analyze the noise sources involved. The intensity noise spectrum is measured up to a 6 GHz frequency range.; We constructed a DSHI (Delayed Self-Heterodyne Interferometer) to measure the laser linewidth. With the DSHI, the laser linewidth is measured under the negative feedback conditions.; Finally, we achieve a narrow linewidth diode laser with negative electrical feedback. The effects of negative electrical feedback are analyzed on the basis of frequency, intensity, and laser bandwidth spectral density. Based on the rate equation, frequency and intensity noise spectral densities are calculated theoretically for the negative electrical feedback using a FP (Fabry-Perot) cavity. The effectiveness of negative electrical feedback is measured based on frequency and laser bandwidth spectrum.