Martin M. Fejer

Scandium Oxide Thin Films Deposited by Dual Ion Beam Sputtering for High-Power Laser Applications

Scandium oxide films were deposited using reactive dual ion beam puttering. At 1 micron, the refractive index of the films is 1.95 and the absorption loss is 18.5 ppm. X-ray photoelectron spectroscopy showed oxygen defects.

Temperature dependent noise in quantum frequency conversion (Conference Presentation)

Hybrid quantum networks will be based on nodes that operate at different wavelengths, requiring quantum channel standardization via quantum frequency conversion (QFC). QFC is typically based on highly efficient sum- or difference-frequency generation in second-order nonlinear materials, such as periodically poled lithium niobate waveguides. The presence of the strong pump beam in such a nonlinear medium leads to unwanted nonlinear processes that produce noise. One of these noise processes is spontaneous Raman scattering (SRS). Typically, the pump is chosen to be the longest wavelength in the second-order nonlinear mixing process so that noise photons at the signal wavelength are produced by the less efficient anti-Stokes Raman scattering process rather than the Stokes scattering process. Since SRS is a temperature-dependent process, lowering the temperature reduces the Raman-scattered photons. We discuss the theory of temperature-dependent Raman scattering and present experimental results of the temperature dependence of dark count rates in a guided-wave QFC device.

Photothermal measurements of absorption in LBO with a "proxy pump" calibration technique

Photothermal technology provides sensitive detection of the optical absorption in bulk materials and coatings. To obtain the absolute absorption numbers it requires a proper calibration. In this work a new, “proxy pump” calibration approach is described. The proxy pump has a wavelength at which the material exhibits high enough optical absorption to be evaluated via direct loss measurements. The pump beam is shaped to have the same spot size as the main pump at which the optical absorption of the material is to be determined. Once the thermal field in the material has the same profile both with the proxy and main pump, the sample is self-referenced. Consecutive tests with proxy and main pumps provide absolute absorption numbers. LBO crystals are notorious objects for which the photothermal response is not easy to calibrate since the material has very low absorption in the UV, visible and near IR. In order to calibrate these materials using the above approach we used 2.3 nm laser as a proxy pump. At this wavelength LBO absorbs more than 15 % per cm length. For crystals oriented in XY and YZ planes the photothermal response was found to be 3 times weaker than for Schott glass NG12 with the same amount of absorbed power. With this correction, NG12 glass that has absorption more than 45 %/cm in the wide range of wavelengths can be used as a reference calibration material for LBO crystals.

Vapor-Transport Equilibrated Lightly MgO-Doped Lithium Niobate for Nonlinear Optics

We discuss several properties of lightly-MgO-doped near-stoichiometric lithium niobate in comparison with other ferroelectric nonlinear materials. Recent results on green light generation and potential advantages over 5 mol-% MgO-doped congruent lithium niobate are described.