摘要:

Optical gain measurements have been performed on several of the lower order modes of a multimode polyimide planar waveguide doped with the laser dye cresyl violet 670. A transverse pumping geometry was employed, resulting in larger gain for higher order modes. In a 21‐mm‐long device, an amplification of 14.4 dB was achieved for the sixth order guided mode at a wavelength of 670 nm. The photostability performance of the waveguide is comparable to the results reported for rhodamine‐doped organically modified silica gels. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117013

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We demonstrated low‐noise and high‐power GaAlAs laser diodes with small astigmatism. The low‐noise characteristics are realized by self‐sustained pulsation due to the saturable absorption of a single‐quantum‐well located close to the triple‐quantum‐well active layer. The high‐power and small‐astigmatism characteristics are achieved by using a real refractive index guided self‐aligned structure. The lasers showed a relative intensity noise less than −130 dB/Hz under 10% optical feedback in a very wide output‐power range (5–35 mW), a stable fundamental transverse mode up to 150 mW, and astigmatism less than 1 &mgr;m. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117014

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Three kinds of electro‐optic devices composed of the inverted domains in LiNbO3substrates were fabricated. The devices are induced and controlled by applying an electric field. The three devices are: (i) a cylindrical lens with an aperture of 340 &mgr;m and length of 10 mm, which can tune the focusing length from 20 to 50 mm depending on an electric field ranging from 250 to 150 V/mm, (ii) an optical switching device composed of a periodically inverted domain structure, which can reflect the whole power of an incident light beam by applying an electric field of 700 V/mm, and (iii) a deflection device with a deflection angle of about 5°, depending on an electric field of 750 V/mm. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117015

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Front‐illuminated PtSi–n–Si Schottky barrier photodiodes have been developed for the ultraviolet and vacuum ultraviolet spectral range. Their spectral responsivity was determined in the 120–500 nm spectral range by use of a cryogenic electrical substitution radiometer operated with spectrally dispersed synchrotron radiation. For wavelengths below 250 nm, the spectral responsivity is about 0.03 A/W, comparable to that of GaAsP Schottky photodiodes. Unlike the GaAsP diodes, the new PtSi–n–Si diodes have a spatially uniform response which is virtually stable after prolonged exposure to short wavelength radiation. Even after a radiant exposure of 150 mJ cm−2at wavelength 120 nm, the relative reduction in spectral responsivity remains below 0.2%. Due to these features, this type of photodiode is a promising candidate for use as secondary detector standard in the ultraviolet and vacuum ultraviolet spectral ranges. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117016

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

By using the moving grating technique, without an applied electric field, it is possible to significantly increase the steady‐state two‐beam coupling gain in photorefractive Sn2P2S6. Another technique of gain enhancement consists of cooling of the sample to −30 °C. The measured data confirm the existence of two out‐of‐phase gratings in Sn2P2S6generated by charge carriers of different sign, with relaxation times of 70 ms and 500 s. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117017

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Time‐resolved‐emission spectra of InGaN and GaN light emitting diodes with different device structure are studied. Result shows that the UV generation from bulk materials and blue and green emissions from single quantum well devices are band edge recombination. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117183

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We reportinvivolaser computed tomographic images of the proximal interphalangeal joint region of a healthy human volunteer’s index finger. The laser computed tomographic (CT) images were obtained with a highly sensitive coherent detection imaging method that is based on the optical heterodyne detection method. These laser CT images are compared at the wavelengths of 715 nm and 1.064 &mgr;m and with images obtained by conventional imaging methods such as x‐ray CT and magnetic resonance imaging. Internal structures of the proximal interphalangeal joint region could be clearly identified in the laser CT images. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117184

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Broadband transmission of ultrasound in water using capacitive, micromachined transducers is reported. Transmission experiments using the same pair of devices at 4, 6, and 8 MHz with a signal‐to‐noise ratio greater than 48 dB are presented. Transmission is observed from 1 to 20 MHz. Better receiving electronics are necessary to demonstrate operation beyond this range. Furthermore, the same pair of transducers is operated at resonance to demonstrate ultrasound transmission in air at 6 MHz. The versatile transducers are made using silicon surface micromachining techniques. Computer simulations confirm the experimental results and are used to show that this technology promises to yield immersion transducers that are competitive with piezoelectric devices in terms of performance, enabling systems with 130 dB dynamic range. The advantage of the micromachined transducers is that they can be operated in high‐temperature environments and that arrays can be fabricated at lower cost. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117185

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A spectroscopic technique, acoustic wave resonance spectroscopy (AWRS), has been developed to study the influence of long wavelength acoustic phonon excitations on surface chemical processes. Results are presented which demonstrate the sensitivity of AWRS to the state and composition of a Pt{100} single crystal sample, using an ultrahigh frequency and amplitude resolution acoustic spectrometer, a vector analyzer. A novel part of the ultrahigh vacuum compatible excitation system is a retractable piezo holder allowing the lithium niobate piezo transducer to be movedinsituinto the bonding position against the side of the sample. Very sharp acoustic resonant modes with aQmerit factor of 1×104appear only when the sample is clean. Carbon contamination reduces drastically both the intensity and the density of the peaks. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117186

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A method to determine elastic constants of high acoustic velocity materials by line‐focus acoustic microscopy is presented. To determine elastic constants the distances between the specular reflection peak and the first interference maximum and minimum of theV(z) curve measured by line‐focus acoustic microscopy were compared to the corresponding distances obtained from aV(z) measurement model that simulates the experiment. Elastic constants of a single‐crystal diamond sample were determined by this method. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117187

出版商:AIP    

年代:1996

数据来源: AIP