Recent advances in SAW laser probe

Recent advances in SAW laser probe techniques encompass measurements of all three major surface wave types (Rayleigh, leaky and STW). The first advance involves improved experimental techniques and data analysis methods. This has led to greatly reduced deleterious effects caused by laser cavity modes and enhanced measurement dynamic range. The time-frequency and position-wavevector dualities have been further exploited for separate examination of waves that are overlapped either in time and frequency or in space and wavevector. Two examples of Rayleigh wave probing demonstrate greater than 100 dB measurement dynamic range from a transversally coupled resonator filter, and clear separation of different waves in a single-bounce RAC device. The second advance concerns probing the predominately transversely polarized leaky surface waves by the knife-edge based laser probe. Adequate probe sensitivity has enabled quantitative data analysis, resulting in extraction of directly relevant device design parameters. Examples of leaky wave probing demonstrate a directly measured leaky wave dispersion relationship for 36°-LiTaO₃, and the measurement of mode profiles in a longitudinally coupled cavity resonator filter. The third advance concerns a technique for probing the purely transversely polarized STW. Based on the photoelastic effect, this new technique has enabled practical STW probing in packaged devices. Results from an off-the-shelf 600-MHz narrowband quartz SSBW filter are presented