Gerald L. Vossler

Imaging through scattering media with holography

Various holographic methods for imaging through scattering media such as biological tissue are described. The methods utilize light of either reduced spatial coherence or reduced temporal coherence.

High frequency ultrasound imaging using an active optical detector

Optical detection of ultrasound has numerous advantages over traditional piezoelectric methods. These systems offer noncontact inspection, rapid scanning capabilities, fine spatial sampling, and large bandwidths. In addition, difficulties associated with conventional ultrasound imaging systems such as cross-talk between elements, electrical connections, and electromechanical resonances are greatly reduced or even eliminated. Because of this, high frequency phased arrays for ultrasound detection can be emulated by accurately positioning and focusing optical beams on a suitable surface, which defines array elements. However, optical systems have lower sensitivity than their piezoelectric counterparts, limiting their widespread use in ultrasound imaging. Active optical detection offers a solution. An active ultrasound detector consisting of a neodymium-doped glass waveguide laser with an optical demodulation system, was built demonstrating enhanced sensitivity while preserving the benefits of traditional passive optical detection.

Integrated-optic dispersion compensator that uses chirped gratings

An integrated-optic dispersion compensator that uses chirped waveguide gratings is designed and fabricated. The 7-mm-long chirped grating is realized by a recently proposed method of curving a waveguide through a uniform grating. At 800 nm, the fabricated device exhibits a reflection bandwidth in excess of 0.5 nm and a nearly quadratic phase response corresponding to a fiber dispersion–length product of 58 ps/nm. The phase response reported is measured interferometrically with a narrow-band, tunable Ti:sapphire laser. Extending this technology to 5-cm-long gratings should permit dispersion compensation of 50-km-long fiber lengths at 1.55 μm.

Phase response measurement technique for waveguide grating filters

A simple interferometric technique is described which can be used to accurately measure the phase response of waveguide grating filters. A narrowband, tunable Ti:sapphire laser is used in a Michelson interferometer configuration, where light reflected from a waveguide grating filter is combined with a reference beam. The intensity of the combined beams is measured as the wavelength of the Ti:sapphire laser is tuned. The measured intensity exhibits a quasisinusoidal wavelength dependence, from which the phase response of the filter can be deduced. This method is successfully demonstrated using both an integrated optic waveguide grating filter and a bulk grating pair.

An active optical detector for high frequency ultrasound imaging

Optical detection of ultrasound has numerous advantages over traditional piezoelectric methods. These systems offer non-contact inspection, rapid scanning capabilities, fine spatial sampling and large bandwidths. In addition, difficulties associated with conventional ultrasound imaging systems such as cross-talk between elements, electrical connections, and electromechanical resonances are greatly reduced or even eliminated. However, optical systems have lower sensitivity than their piezoelectric counterparts, limiting their widespread use in ultrasound imaging. Active optical detection offers a solution. An active ultrasound detector, consisting of a neodymium-doped glass waveguide laser with an optical demodulation system, was built demonstrating enhanced sensitivity while preserving the benefits of traditional passive optical detection.

Evaluation of holographic methods for imaging through biological tissue

Different holographic methods for imaging through biological tissue are evaluated and compared. The role of the source autocorrelation function is analyzed. A graphical plot for performance evaluation is introduced. Experimental results for the various methods are given, and possibilities for further development are indicated.

Erbium:ytterbium planar waveguide laser in ion-exchanged glass

Erbium-ytterbium co-doped is an attractive system for short, efficient lasers and amplifiers operating in the 1.5 micron band. Co-doping permits a cooperative cross-relaxation process to transfer energy from excited ytterbium ions to the erbium system. This process can be used as a transfer energy from excited ytterbium ions to the erbium system. This process can be used as a pumping mechanism at 980 nanometers to significantly increase the absorbed pump power.Efficient energy transfer between the ytterbium and erbium ions enables the operation of compact laser devices with low erbium concentration, thus avoiding parasitic effects. The material parameters of a co-doped glass, including the cross-relaxation coefficient, are measured. A rate equation analysis of the co-doped system is developed, and approximate analytic expressions are derived for the lasing threshold, slope efficiency, and maximum output power. Short, ion-exchanged, waveguide lasers are fabricated in co-doped erbium-ytterbium glass. Lasing is achieved around 1537 nanometers with a launch power threshold and slope efficiency of approximately 15 milliwatts and 5.5 percent, respectively.

Use of holography for imaging through inhomogeneous media

Electronic holography for imaging through biological tissue is described. A number of processes are given, including the holographic implementation of the first arriving light method, the broad source method, as well as variations on these methods. The equipment is discussed in some detail, including the camera-computer interactions.

Imaging through biological tissue with holography

Various holographic methods of imaging through highly scattering media such as biological tissue are described. Experimental results are given.