摘要:

Clinical trials using accelerated heavy charged‐particle beams for treating cancer and other diseases have been performed for nearly four decades. Recently there have been worldwide efforts to construct hospital‐based medically dedicated proton or light‐ion accelerator facilities. To make such accelerated heavy charged‐particle beams clinically useful, specialized instruments must be developed to modify the physical characteristics of the particle beams in order to optimize their biological and clinical effects. This article reviews the beam modifying devices and associated dosimetric equipment developed specifically for controlling and monitoring the clinical beams.

ISSN:0034-6748    

DOI:10.1063/1.1143946

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The methodology and apparatus are described to perform tunable repetition rate optical spectroscopic measurements using high‐power visible diode lasers. Here, a train of picosecond pulses interrogates a material, a sample, or a device under test. The response of the sample or device varies as the pulse repetition frequency changes. Using an rf modulated high‐power AlGaInP 670‐nm diode laser, the pulse train repetition frequency may be smoothly varied from the kHz range up to the GHz range. The power and the pulse width may be kept constant by adjusting the rf power and the dc injection current. This procedure is automated through computer control. Here we describe the details of our particular setup and present examples of the technique.

ISSN:0034-6748    

DOI:10.1063/1.1143947

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Performance and limitations of laser frequency stabilization based on the locking to the side of an absorption line are discussed: experimental results of spectroscopic measurements and of the stabilization of 1543‐nm DFB laser diodes to ammonia absorption lines are presented.

ISSN:0034-6748    

DOI:10.1063/1.1143948

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe a new diode laser current controller which features low current noise, excellent dc stability, and the capacity for high‐speed modulation. While it is simple and inexpensive to construct, the controller compares favorably with the best presently available commercial diode laser current controllers.

ISSN:0034-6748    

DOI:10.1063/1.1143949

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A system of optical beating spectroscopy has been newly developed for hyper‐resolution Brillouin scattering. Frequency resolution as high as 1 kHz was obtained, far beyond the limit of the classical Fabry–Perot interferometer which is commonly used in ordinary experiments. This system is useful over the frequency range from 104to 109Hz at present. Experiments for Rayleigh and/or Brillouin spectra were performed in water, toulene, and carbon disulfide to demonstrate the performance of this system.  

ISSN:0034-6748    

DOI:10.1063/1.1143950

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A pump‐probe picosecond time‐resolved Raman spectrometer has been constructed using a dye laser synchronously pumped by a cw mode‐locked Nd:YAG laser and a high repetition rate (2 kHz) dye amplifier pumped by the frequency doubled output from a cw Nd:YAG regenerative amplifier. Transform‐limited picosecond pulses with 3.5 cm−1wave number width and 3.2 ps temporal width are obtained at the wavelength of 588 nm. The second harmonic of these pulses is generated at 294 nm and is used for pumping, while the remaining visible pulses are used for probing resonance Raman scattering. The cross‐correlation time between the pump and probe pulses is 4.1 ps. The temporal profile of the laser pulse is found to be very close to the sech2shape. The wave number resolution of the system is estimated to be 3.5 cm−1according to the Tailor criterion. The time resolution is estimated to be 2.2 ps using a criterion newly proposed in the present paper. Time‐resolved Raman spectra ofS1trans‐stilbene andS1p‐terphenyl are presented to demonstrate the capability of the constructed spectrometer.

ISSN:0034-6748    

DOI:10.1063/1.1143951

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe a spectrometer (visible‐ultraviolet photon energy range) for the measurement of reflectance‐difference spectra of cubic semiconductors. The spectrometer employs a photoelastic modulator to modulate the polarization of the light incident on the sample and allows for a simple procedure to correct the measured spectra for parasitic components associated with such modulation. The instrument reported has a higher throughput than more conventional setups. To illustrate the spectrometer performance we report on reflectance‐difference spectra of (001) oriented GaAs single crystals doped with silicon donors at a level of 1018/cm3.

ISSN:0034-6748    

DOI:10.1063/1.1143952

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A new Fourier transform infrared phase‐modulated ellipsometer is presented. It combines the high frequency provided by a photoelastic modulator (37 kHz) with the low frequency of the Fourier transform infrared spectroscopy (<1 kHz), by means of a numerical data acquisition system. A full spectrum recording (from 900 to 4000 cm−1) can be achieved in 2 s. Thus, it allows its adaptation for kineticinsitustudies. The optical setup and the data reduction procedure are presented. In particular, a self‐consistent spectral calibration procedure is described in detail. The precision in &PSgr; and &Dgr; increases from 0.3° to 0.02° when increasing the integration time from 2 to 760 s. The examples shown in this article illustrate the high sensitivity to identify and analyze the absorption vibration variations of ultrathin films (a few angstroms thick).

ISSN:0034-6748    

DOI:10.1063/1.1143953

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A design is proposed for a stable infrared source suited to absorbance measurements. The source is a parallelepipedic cavity of tantalum, heated to 2600 K, with an apparent emissivity in excess of 0.7. It is observed to be three times brighter at 3000 cm−1than the 1440‐K SiC bar. A model is constructed in order to estimate the temperature distribution. For this kind of source, the temperature and emissivity are found to be quite uniform. A comparison between estimated and experimental values of temperature and emissivity is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143954

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The method of sine and cosine Fourier transforms with a phase correction, well known in NMR and traveling wave Fourier transform microwave spectroscopy, is examined for the pulsed beam Fabry–Perot cavity. The validity of this approach is closely related to the result, noted previously elsewhere [J.‐L. Le Goue¨t and P. R. Berman, Phys. Rev. A20, 1105 (1979), and F. Rohart and B. Macke, J. Phys.41, 837 (1980)] that only the polarization spatial harmonic that projects onto the driven fundamental mode of the cavity contributes appreciably to the free induction decay signal. When the full signal is recorded after a short polarization pulse, an absorption line shape function in the low power limit for a single nondegenerate transition can be recovered as an angular distribution weighted integral over the coordinate &thgr; between the nozzle axis and a point on the cavity axis of Doppler‐shifted Voight profiles. Passage of the beam through the transverse Gaussian profile of a TEM00qmode contributes an effective line broadening temperature. These results are a direct extension of a semiclassical derivation given earlier [E. J. Campbell, L. W. Buxton, T. J. Balle, and W. H. Flygare, J. Chem. Phys.74, 813 (1981), and E. J. Campbell, L. W. Buxton, T. J. Balle, M. R. Keenan, and W. H. Flygare, J. Chem. Phys.74, 829 (1981)]. Analytical results are derived using simplified cavity mode functional forms. Calculations using the exact mode expressions are reported. The relation between this approach and the direct absorption method is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1143955

出版商:AIP    

年代:1993

数据来源: AIP