This dissertation is mainly concerned with increasing the pump power absorption in optical refrigeration of solids and photo-acoustic spectroscopy of trace gases using optical cavities. Enhancing the absorption is key to reaching lower temperatures in optical refrigeration and achieving better sensitivity in photo-acoustic spectroscopy.
We have used intra-cavity and coupled-cavity absorption enhancement techniques to increase the absorption in Ytterbium doped Yttrium Lithium Fluoride (Yb3+:YLF) crystals. For this purpose, we have developed tunable high-power narrow-linewidth InGaAs/GaAs vertical external-cavity surface-emitting lasers (VECSELs) operating at 1020 nm, the optimal cooling wavelength for Yb:YLF. By inserting a 7% Yb:YLF sample inside the resonator of the VECSEL, we have cooled it to 130±1 K. It has been shown that due to high intra-cavity power, saturation of pump absorption reduces the absorbed power in intra-cavity cooling. We have also utilized a coupled-cavity geometry to enhance the absorption. In this method, the cooling sample is placed inside a Fabry-Perot cavity which is used as an effective output coupler for the VECSEL. With this technique we have been able to cool a 10% Yb:YLF crystal to 145±1 K. Advantages and challenges, including cavity design, wavelength stabilization techniques, and cooling sample choice for optimal cooling are discussed in both cases.
We have also utilized critical coupling (or impedance) matching condition in two coherently coupled Fabry-Perot cavities to enhance the absorption in photo-acoustic detection of trace gases. In this novel technique, by adjusting the reflectivity of the first Fabry-Perot cavity, the impedance matching can be achieved for a wide range of absorption coefficients for the second cavity, where the acoustic detection is performed. Normalized noise-equivalent absorption coefficient of 5×10^(-10) cm^(-1) W∕√Hz is measured.
Level of Degree
Physics & Astronomy
First Committee Member (Chair)
Second Committee Member
Third Committee Member
Keith A. Lidke
Fourth Committee Member
Michael J. Marin
Ghasemkhani, Mohammadreza. "Cavity Enhanced Optical Refrigeration and Spectroscopy." (2018). https://digitalrepository.unm.edu/phyc_etds/176