摘要:

A dc superconducting quantum interference device (SQUID) modulation and feedback circuit operating at a modulation frequency of 16 MHz has been constructed. Using a novel wide band superconducting thin film transformer to impedance match the SQUID to a rf amplifier allows the system to operate at the SQUID noise level for most types of low‐TCSQUIDs. This system has a closed loop bandwidth exceeding 2.5 MHz and a slew rate greater than 1×106&Fgr;0/s at frequencies up to 1 MHz. This greatly improved performance compared to existing modulation methods can be obtained without enhancing the transfer function of the SQUID. The system allows low‐ and high‐TCSQUID magnetometers and gradiometers to be operated totally unshielded without unlocking in the dc, 60 Hz, and radio frequency electromagnetic fields present in most SQUID applications. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147082

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have developed a current preamplifier that operates in a liquid‐helium bath cryostat. It has been optimized for the measurement of dynamical electric‐current fluctuations (noise) of high‐impedance sourcesR≳100 M&OHgr;. A bandwidth of up to 400 kHz has been achieved by effectively minimizing the capacitance of the input transistor with a dynamical feedback. The amplifier measures current noise in a scanning tunneling microscope (STM). It enables the measurement of shot noise for currents as low as 30 pA (sampling rate 5 s) for a high‐impedance source with a resistance ofR≳1 G&OHgr;, a value typical for tunneling resistances in STM. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147083

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An apparatus to load gases to the sample chamber of the diamond‐anvil cell has been devised. The apparatus is driven by a conventional 50 ton hydraulic press and no gas compressor is required. The gas from a commercial gas bomb is compressed to 150 MPa and loaded into the diamond‐anvil cell sample chamber. After loading, the pressure of the diamond‐anvil cell is increased further using the lever and spring mechanism. This kind of gas loading apparatus will become indispensable not only for studying gaseous materials themselves, but also for making precision measurements at high pressures and high temperatures under hydrostatic conditions. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147084

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Wavelength detection of monochromatic light beams can be achieved with a pair of optical sensors located behind a linear variable filter. The active area of one sensor increases, whereas that of the other sensor decreases along the direction of increasing value of transmission wavelength of the filter. By computing the ratio of the photoresponse of one sensor to the other, the wavelength can be obtained from a calibration chart. Proof‐of‐concept wavelength detectors were constructed using photoresistive superconductor sensors. Results obtained for the spectral range of 700–1100 nm are presented and discussed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147085

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A novel heating element powered by laser radiation via an optical fiber has been demonstrated. Temperatures approaching 2000 °C can be obtained with only a few watts of absorbed power. A prototype device has been used to join gold wires. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147086

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We describe a modification to Newport Corporation’s BV‐100 double solenoid pulsed molecular‐beam valve that replaces the Viton tip seal with an O‐ring‐based plug. This alteration produces the same characteristic short and cold gas pulses as the originally described beam valve without the difficulties associated with replacing the seal. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147087

出版商:AIP    

年代:1996

数据来源: AIP