AVS 51st International Symposium
    Thin Films Wednesday Sessions
       Session TF-WeM

Paper TF-WeM5
Improved Optical Heterodyne Detected Transient Grating Method by using a Thin Film Grating

Wednesday, November 17, 2004, 9:40 am, Room 303C

Session: Optical Thin Films
Presenter: K. Okamoto, California Institute of Technology
Authors: K. Okamoto, California Institute of Technology
Z. Zhang, California Institute of Technology
D.T. Wei, Wei & Assoc.
A. Scherer, California Institute of Technology
Correspondent: Click to Email
Transient grating (TG) spectroscopy based on the third order nonlinear optical effect has been applied to material, chemical, and biological research. Optical heterodyne detected (OHD) TG measurements have been reported by several groups, but experimental setups were mostly complicated. Here, we demonstrate a convenient new technique of OHDTG by transferring a pattern directly from a metal film grating into sample solution. This method has the same advantages of existing OHDTG techniques but the setting is much simpler. Thin film gratings having submicron periods are fabricated by: evaporating metal on a glass substrate, laser beam writing lithography, and chemical etching. The narrowest metal width of our grating is 333nm. The fabricated grating is then placed in the front side of a quartz cell containing the sample solution with 10mm optical pass length. An UV pump beam (a frequency-tripled Nd:YAG laser) casts a shadow from the grating to the sample solution such that a dark/bright pattern is formed in the solution liquid called transient grating. Such spatial modulation of the optical intensity induces changes of temperature, density and the molecular excitation. Through this transient grating, the modulated refractive index and absorbance of sample materials can be detected by the diffraction of a probe beam (a He-Ne laser). By analyzing the probe beam diffraction, we can obtain the intensity and dynamics of the modulated parameters named above. This technique has many advantages compared with existing OHDTG techniques; such as: (1) simple setting, easy alignment, (2) high signal stability, (3) easy control of phase shift, and (4) quick interchange of grating periods. We shall demonstrate this technique from several materials and discuss about the potential benefit of this new technique.