Gisia Beydaghyan

Enhanced photochromism in nanostructured molybdenum trioxide films

We present evidence of enhancement of photochromism in nanostructured thin films of molybdenum oxide fabricated by glancing angle deposition. The strong correlation of coloration response with the internal surface area of the films provides evidence of the importance of nanostructuring on the photochromic effect and the vital role played by the availability of water in the photochromic mechanism.

Mid-IR laser beam quality measurement through vanadium dioxide optical switching.

We present a beam characterization system for infrared lasers which can measure both wavefront and beam profile with visible detectors. While previous studies demonstrated the conversion from the visible to the near infrared, this device exploits the wavelength conversion from the infrared to the visible, which is based on the refractive index change because of the optical switching of a vanadium dioxide layer. This technique can be applied over a broad spectral range from the visible to the infrared and potentially to the terahertz.

Enhanced electrochromic properties of heat treated nanostructured tungsten trioxide thin films

Nanostructured tungsten trioxide films were fabricated with the technique of glancing angle deposition (GLAD) in a thermal evaporation chamber with a base pressure of 1.3 × 10 −4 Pa. Films were deposited at vapor incidence angles of 0°, 20°, 40°, and 50° with film thickness varying between 160 and 200 nm, as determined by spectroscopic ellipsometry. After deposition, samples were heated for 1 h in air at 400 °C and were subsequently intercalated with small amounts (5 to 15 nm) of lithium by dry lithiation, a technique developed in our laboratory. Compared with our previous work on as-deposited nanostructured films, these samples showed significantly enhanced coloration in the infrared region. It was found that the films exhibited an absorption- based coloration in the lower wavelengths as well as an increased reflection in the infrared region. Morphological investigation by atomic force microscopy (AFM) showed grain agglomeration and increased surface roughness upon heating. Our studies further indicate that grain agglomeration significantly contributes to the superior coloration properties of the films.

Single-material multilayer with enhanced photoactivity

Molybdenum trioxide (MoO3) patterned at the nanometer scale is combined with the same material in its bulk form to produce Bragg mirrors with enhanced photoactive properties. MoO3 undergoes coloration with exposure to UV light but a multilayer structure which alternates between nanostructured and bulk MoO3 is 2.5 times more effective. Measurements with various multilayer arrangements suggest the proximity of bulk and nanostructured MoO3 favors the photoreaction with structural water. A possible minor contribution from electronic band shifting is also discussed.

Compact linearly polarized ceramic laser made with anisotropic nanostructured thin films

A novel method is proposed for the fabrication of polarizing laser mirrors for compact solid-state lasers using glancing angle deposition. Changing the inclination angle and the azimuthal orientation of the substrate during deposition allows one to create and control in-plane birefringence of a deposited thin film by changing its nanostructure. Principal refractive indices of tungsten trioxide films were determined for various deposition angles using transmission and reflection ellipsometry. High-reflectance contrast between orthogonal linear polarization directions was obtained using a single material without any additional processing steps. These birefringent films were the building blocks of a Bragg mirror that was tested as an output coupler of a (Yb0.1Y0.9)3Al5O12 ceramic laser in a laser-diode end-pumped configuration. Continuous-wave, linearly polarized, transverse single-mode laser emission was obtained at a wavelength of 1030 nm with a polarization extinction ratio higher than 973 (30 dB).

Continuously variable, electrically addressed beam splitter based on vanadium dioxide

Vanadium dioxide (VO(2)) is used to implement an electrically addressable beam splitter with continuously variable splitting ratios. The electrical control of temperature in a thin VO(2) layer is used to vary its transmission/reflection behavior. The technique is characterized for various incidence angles, s- and p-polarizations, and the wavelength range of 400-2000 nm. Splitting ratios continuously tunable over four orders of magnitude are reported.

Fabrication of blue light-blocking optical interference coatings by the solgel method

We report on the solgel method of fabrication of thin films of high optical quality and with tunable index of refraction. The resulting coatings are hard, durable and robust against humidity and common organic solvents. Bragg mirrors and edge filters have been made by stacking these films. A blue light-blocking edge filter made by 2×21 stacked layers shows a transmittance of less than 1% in the stop band region while maintaining a high transmittance of over 80% in the rest of the visible spectral region with an integrated photopic transmittance of 89.7%.

Optical Phase Control at the Nanometer Scale in Vanadium Dioxide

Large refractive index changes during phase transition in vanadium dioxide are exploited to control the phase of a light at 1300 nm over distances of less than 100 nm without altering other properties of light.

Effect of Sputter Pressure on the Optical Properties of Sputter-Deposited Titanium Oxide Thin films

The refractive index of the titanium oxide thin films deposited with DC magnetron sputtering was tuned by adjusting the sputtering gas pressure during deposition. This effect may be exploited for the fabrication of optical interference coatings.