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12 Nov 2001

Volume 79, Issue 20, pp. 3215-3366

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Schlieren imaging of laser-generated ultrasound

Dilhan K. L. Don-Liyanage and David C. Emmony

Appl. Phys. Lett. 79, 3356 (2001); http://dx.doi.org/10.1063/1.1418028 (2 pages) | Cited 6 times

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The interaction of a pulse from a Q-switched laser with a metal in water is the basis for the laser peening process where the metallurgical properties are modified. An investigation of the process, using schlieren imaging, shows that high-frequency ultrasound is generated when the metal is in the form of a thin plate. The period of the ultrasonic waves in the water is given by the plate thickness and the velocity of longitudinal sound waves in the metal. Ultrasonic wave trains with a frequency of 7.5 MHz up to 10 μs long are shown. © 2001 American Institute of Physics.
Show PACS
42.62.-b Laser applications
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Bx Metals, semimetals, and alloys
62.65.+k Acoustical properties of solids
07.68.+m Photography, photographic instruments; xerography
61.82.Bg Metals and alloys
79.20.Ds Laser-beam impact phenomena

Sub-attonewton force detection at millikelvin temperatures

H. J. Mamin and D. Rugar

Appl. Phys. Lett. 79, 3358 (2001); http://dx.doi.org/10.1063/1.1418256 (3 pages) | Cited 135 times

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A 290-nm-thick single-crystal silicon cantilever has been cooled in vacuum to a temperature of 110 mK in order reduce its thermal motion and thereby improve the achievable force resolution. Since the thermal conductivity of the silicon cantilever is extremely low at millikelvin temperatures, an improved optical fiber interferometer was developed to measure the subangstrom thermal motion with optical powers as low as 2 nW. At the lowest temperature, the cantilever exhibited a quality factor of 150 000 and achieved a noise temperature of 220 mK, with a corresponding force noise of 820 zN in a 1 Hz bandwidth. © 2001 American Institute of Physics.
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07.10.Pz Instruments for strain, force, and torque
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.10.Cm Micromechanical devices and systems
42.81.Pa Sensors, gyros
07.60.Ly Interferometers

Generation of coherent acoustic phonons in strained GaN thin films

Yue-Kai Huang, Gia-Wei Chern, Chi-Kuang Sun, Yulia Smorchkova, Stacia Keller, Umesh Mishra, and Steven P. DenBaars

Appl. Phys. Lett. 79, 3361 (2001); http://dx.doi.org/10.1063/1.1418450 (3 pages) | Cited 16 times

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Coherent acoustic phonon oscillations were generated and studied in strained GaN thin films. Inside the bulk GaN film, the longitudinal interference of an ultraviolet femtosecond pump pulse created periodic carrier distribution that screened out the strain-induced piezoelectric field and initiated the coherent longitudinal acoustic phonon oscillations corresponding to the carrier periods. The created coherent phonon oscillation modulated the piezoelectric field thus modified the absorption property of the GaN thin film through Franz–Keldysh effect. This time-dependent absorption modulation was reflected in the transmission variation of the followed probe pulses, resulting a long decay time ∼300 ps for the initiated coherent phonon oscillations. © 2001 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.55.-a Thin film structure and morphology

Self-focused electron beams produced by pyroelectric crystals on heating or cooling in dilute gases

J. D. Brownridge and S. M. Shafroth

Appl. Phys. Lett. 79, 3364 (2001); http://dx.doi.org/10.1063/1.1418458 (3 pages) | Cited 20 times

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Self-focusing, spatially stable, electron beams are produced by cylindrical pyroelectric crystals such as LiNbO3 in dilute gases on cooling provided that heating is done from the +z base. Beam energies up to 170 keV have been observed. A 4 mm diameter×10 mm crystal heated to 160 °C gives rise to spatially stable beams with a focal length of 22 mm and a 1 mm spot size. Here we present photographic as well as electronic proof of the existence of these electron beams. © 2001 American Institute of Physics.
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79.40.+z Thermionic emission
77.70.+a Pyroelectric and electrocaloric effects
41.75.Fr Electron and positron beams
41.85.-p Beam optics
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