Gerald Diebold
Professor of Chemistry:
Chemistry
Phone: +1 401 863 3586
gerald_diebold@brown.edu
The process of sound wave generation by light, known as the photoacoustic effect, is quite general and can be initiated in liquids and solids as well as gases. The Diebold group has focused on photoacoustic research for the last two decades, investigating fundamental phenomena and new effects. Much of the current effort in the group has been devoted to transient grating experiments, a photoacoustic recording method that has high time resolution. The most recent research directions for the Diebold group have been x-ray phase contrast imaging and imaging with the ultrasonic vibration potential. The latter is a completely new imaging modality.
Biography
Professor of Chemistry, 1988-present
Associate Professor of Chemistry, 1984-1987
Assistant Professor of Chemistry, Brown University, 1978-1984
Stanford University, 1977-1978 (Postdoctoral Fellow with Richard N. Zare)
Columbia University, 1976-1977 (Postdoctoral Fellow with Richard N. Zare)
Boston College, 1974-1975 (Postdoctoral Fellow with David L. McFadden)
Boston College, 1974, Ph.D., Physics (with George J. Goldsmith)
University of Notre Dame, 1965, B.D., Physics
Interests
In 1898 Alexander Graham Bell found that when an infrared active gas is exposed to modulated radiation, a periodic heating of the gas takes place causing sound waves to be generated. This process of sound wave generation, now known as the photoacoustic effect, is quite general and can be initiated in liquids and solids as well as gases. Perhaps the outstanding feature of the photoacoustic effect is its remarkable sensitivity when a laser is used as the optical source. We recently have been investigating another fascinating property of the photoacoustic effect. When a pulsed laser irradiates a particle, the time profile of the emitted pressure wave is determined by both the geometry of the particle and its acoustic properties. The first stage in the research done here was development of theory for determining the time profiles of the waves by solving the wave equation for pressure. Later, experiments with a pulsed Nd:YAG laser were carried out to verify the theory and to find its limitations. Thus, an analytical technique, a kind of spectroscopy of particles, has been developed whereby a recording of a photoacoustic wave can be used to determine the geometry of a body, its sound speed, and density. A development that came as a result of the work with particles was the investigation of a photoacoustic device that acted as an acoustic laser. That is, when layers of a weak optical absorber are juxtaposed between transparent layers that have identical acoustic transit times, the acoustic reflections add coherently in time. Thus, if the layered structure is irradiated by a laser modulated at the correct frequency, a highly directional acoustic beam with many of the properties of a distributed feedback laser is produced. We have also investigated the photoacoustic effect that is produced in India ink, which is a suspension of carbon in water. We have found a surprising "giant" photoacoustic effect where the amplitude of the effect is roughly 2000 times as large as it would normally be in a dye solution. The remarkable size of the effect comes as a result of chemical reactions that take place between carbon and water at the high temperatures produced by the laser. The mix of reaction products turns out to be fascinating in itself - the pulsed laser creates conditions of high pressure and temperature where a distribution of products is produced that is not found under any other laboratory conditions.
We are initiating a program of tissue imaging using the ultrasonic vibration potential in colloidal suspensions. The work is motivated by the search for more sensitive methods for detection breast tumors—methods to detect the presence of tumors at their earliest stages of development. The primary difficulty in using x-rays for mammography is that the contrast mechanism for distinguishing tumors from healthy tissue depends on density differences, which are not so large as to allow early detection. The vibration potential offers the possibility of high sensitivity detection precisely as a result of its contrast mechanism. We have found that the ultrasonic vibration potential is roughly fifty times that for muscle and fatty tissue. Since tumors are highly vascularized, that is, they are surrounded by a large network of blood vessels, hence, a detector of blood concentration becomes a detector of tumors.
Colloids are suspensions of charged particles in a liquid with a counter charge distributed in the fluid around each particle. The counter charge, which is normally a spherical distribution around the particles, gives the solution overall charge neutrality and stabilizes the suspension against particle agglomeration. When sound propagates through a suspension where the particles have either a higher or lower density than that of the surrounding fluid, the amplitude and phase of the particle motion, owing to the difference in inertia between the particle and the volume of fluid it displaces, differs from that of the fluid so that fluid flows back and forth relative to the particle on alternating phases of the acoustic cycle. Since the counter charge is carried by the fluid, the oscillatory motion of the fluid relative to the particle distorts the normally spherical counter charge distribution creating an oscillating dipole at the site of each particle, which, added over a half wavelength of the sound wave, results in a macroscopic voltage that can be recorded by a pair of electrodes placed in the solution.
We also have a program for the use of x-ray phase contrast to detect tumors. X-ray phase contrast imaging refers to using the phases introduced in an x-ray beam as it traverses a body to give contrast. All materials have indices of refraction (at any wavelength) which determine the amount of refraction a beam of radiation passing through the body. X-radiation as it passes through a body is deflected as it passes through soft tissue an amount that depends on the presence of density gradients. The most visible features of this deflection process are seen in the image where there are interfaces between two materials of different density. Conventional x-ray mammograms do not show the effects of the bending of the trajectories of the x-rays in the images because of the large size of the radiation source—essentially, the fine phase contrast features are averaged out by the large source size of a conventional x-ray tube. The advantages of the unique contrast mechanism are being explored for use as an early tumor detection method.
Awards
Distinguished Scholar Award, Korea Science and Engineering Foundation, 2004
Innovator Award, U.S. Army Medical Research And Materiel Command, 2002
Alcoa Foundation Research Award, 1991
Best Paper Award (with coauthors) SPIE/BIOS 2005 given by Fairway Medical
NSF Graduate Traineeship
Affiliations
Professional:
Organizing Committee for BIOS03-Photonics West Conference, San Jose
Session Organizer, NIST symposium on Thermophysical Properties 2006
SPIE Conference; Program Committee, 2006
Director: International Photoacoustic and Photothermal Society 2001-present
Memberships:
American Chemical Society
American Physical Society
Funded Research
US Army Medical Research And Materiel Command:
2002-2007, "Electroacoustic Tissue Imaging", $1,987,165
US Department of Defense Breast Cancer Imaging Research Program:
2003,"High-Resolution X-Ray Phase Contrast Imaging with Acoustic Tissue-Selective Contrast Enhancement" $500,000 with Christoph Rose-Petruck
US Department of Energy:
2006-2008, "Photoacoustic and Thermal Effects in Particulate Suspensions", $200,000
2003-2006, "Experimental Studies of Photoacoustic and Photochemical Effects." $401,520
2001-2002,"Photoacoustic and Photothermal Effects in Fluids" $90,000
2000-2001, "Photoacoustic and Photothermal Effects in Fluids " $90,000
1999-2000, "Photoacoustic and Photothermal Effects in Fluids" $90,000
1998-1999, "Thermal Generation of the Photoacoustic Effect" $88,000
1997-1998, "Thermal Generation of the Photoacoustic Effect " $88,000
1996-1997, "Thermal Generation of the Photoacoustic Effect" $88,000
1995-1996, "Thermal Generation of the Photoacoustic Effect" $86,000
1994-1995, "Thermal Generation of the Photoacoustic Effect" $86,000
1993-1994, "Photochemical Generation of the Optoacoustic Effect" $58,000
1992-1993, "Photochemical Generation of the Optoacoustic Effect." $86,000
1991-1992, "Photochemical Generation of the Optoacoustic Effect." $94,000
1990-1991, "Photochemical Generation of the Optoacoustic Effect." $80,000
1989-1990, "Photochemical Generation of the Optoacoustic Effect." $80,000
1988-1989, "Thermal Generation of the Photoacoustic Effect." $80,000
1987-1988, "Thermal Generation of the Photoacoustic Effect." $67,000
1986-1997, "Thermal Generation of the Photoacoustic Effect." $68,000
1985-1986, "Photochemical Generation of Optoacoustic Effect." $75,000
1984-1985, "Photochemical Generation of Optoacoustic Effect." $74,442
1983-1984. "Photochemical Generation of Optoacoustic Effect." $74,442
1982,"Photochemical Generation of Optoacoustic Effect." $55,338
ONR Grant:
1999-2002 "Miniature Photoacoustic Detector for Trace Chemical and Biological Warfare Agents" with M. Zimmt $576,502
University Research Council:
2000-2001,"Excited States Lifetime of Biologically Active Hindered Zinc Perfluoralky Perflourophthalocyanine." $15,000 with S. Gorun
National Academy of Sciences:
1994-1995, "COBASE Grant" $2,000
National Institutes of Health:
1983-1984, "Optoacoustic Detection of Carcinogens." $43,076
1984-1985, "Optoacoustic Detection of Carcinogens." $43,000
1985-1986, "Optoacoustic Detection of Carcinogens." $120,287
1986-1987, "Optoacoustic Detection of Carcinogens." $90,371
1987-1988, "Optoacoustic Detection of Carcinogens." $86,677
1988-1989, "Optoacoustic Detection of Carcinogens." $86,677
Alcoa Foundation Research Award $7,500
BRSG, "Laser Stabilized Recording of Small Absorbance Changes in Isotopically Labelled Systems."
"Photoacoustic Detection of Environmental Particulate Contaminants and Photoinduced Electron Transfer in Metal-Organic systems" with M. Zimmt, $9,900 "Narrowband Laser Detection of Optical Rotatory Dispersion" with M. Maricq $7,335
DOD, 1987-1988, "Laser Based Detection of Toxic Compounds." $146,625
National Science Foundation (MRL Grant):
1980, "Inelastic Scattering of Diatomic Molecules from Solid Surfaces." $3,040
1981, "Inelastic Scattering of Diatomic Molecules from Solid Surfaces." $16,075
1982, "Inelastic Scattering of Diatomic Molecules from Solid Surfaces." $19,590
1983, "Materials Research Laboratory, Surface Scattering as Probed with High Resolution Laser Techniques." $24,000
1984, "Materials Research Laboratory, Surface Scattering as Probed with High Resolution Laser Techniques." $24,000
1985, "Materials Research Laboratory, Surface Scattering as Probed with High Resolution Laser Techniques." $19,350
1986, "Materials Research Laboratory, Surface Scattering as Probed with High Resolution Laser Techniques." $29,237
1987, "Materials Research Laboratory, Surface Scattering as Probed with High Resolution Laser Techniques." $29,237
Biomedical Research Support Grant:
1979, "High Sensitivity Detection of Carcinogens." $3000
1980, "High Sensitivity Detection of Carcinogens." $3765
Petroleum Research Fund, 1979, "Experimental Study of Translational Energy and Orientation Effects in Vibration-to-Electronic Energy Transfer." $10,000
American Cancer Society Sub-grant:
1979, "Laser Optoacoustic Detection of Carcinogens." $5,000
1980, "Laser Optoacoustic Detection of Carcinogens." $800
Research Corp:
1978, "Effects of Collision Geometry and Translational Energy in Vibrational-to-Electronic Energy Transfer." $12,850
