摘要:

A polarization modulation microscope designed to detect and spatially resolve the distribution of optically anisotropic domains in microscopic objects is described. An image dissector camera is used as the detection device. The polarization of the light is modulated by means of a photoelastic modulator and a synchronous demodulation amplifier (lock‐in) is utilized to obtain the difference image between the images formed using two orthogonal forms of the incident polarization on the sample. Preliminary results are described for the linear dichroism imaging measurements of polymerized hemoglobin (HbS) in red blood sickle cells. The present limitations of this design are discussed along with various strategies to improve its performance.

ISSN:0034-6748    

DOI:10.1063/1.1139505

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A new method for rapidly acquiring fluorescence spectra from optical probes using an acousto‐optic tunable filter (AOTF) has been developed. The AOTF consists of a piezoelectric transducer bonded to a birefringent crystal. Acoustic waves are generated in the crystal by an applied radio frequency. For a given radio frequency, only a narrow band of optical frequencies will be diffracted. Unlike normal Bragg diffraction which can only be used with collimated light, the AOTF has a large angular aperture (up to 28 deg) and can therefore be coupled to an uncollimated broadband white light source, photomultiplier tube, or camera. Using the device and a xenon–mercury arc lamp, excitation and emission spectra of the fluorescentpH probe BCECF were acquired in 17 ms (spectral resolution=4 nm). Rapid wavelength switching or modulation of selected wavelengths was achieved at ∼105Hz. The device is also capable of spectral imaging with a spatial resolution of greater than 100 lines/mm.

ISSN:0034-6748    

DOI:10.1063/1.1139506

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The theories of the feedback and vibration isolation systems have been developed to illuminate the essential points in the design and operation of the scanning tunneling microscope (STM). By analyzing a delay differential equation, we can understand the behavior of feedback and estimate the necessary gain and time constant for the best performance of the STM. Design considerations for a vibration isolation system consisting of spring suspension and magnetic damping are discussed with theoretical optimization.

ISSN:0034-6748    

DOI:10.1063/1.1139507

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

This article describes the design of a scanning tunneling microscope (STM) which is suitable for surface science work. Various concepts in mechanical structure and electronic circuitry of the STM have been pursued to optimize its performance. This STM has been designed especially to meet the requirement ofinsitusample preparation and sample transfer in ultrahigh vacuum. The electronics of this STM are capable of taking simultaneous images with opposite polarities of tunneling voltages.

ISSN:0034-6748    

DOI:10.1063/1.1139508

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Thin‐film pyroelectric effect detectors provide a simple means of measuring thermal properties of solid samples. The present work reports a time‐delay theoretical model of thin‐film pyroelectric detection which enables the recovery of thermal diffusivity and thermal conductivity information from the impulse response of the pyroelectric system.

ISSN:0034-6748    

DOI:10.1063/1.1139509

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Frequency‐modulation time‐delay spectrometry (FM‐TDS) has been implemented in photopyroelectric measurements of thermal diffusivity, on a series of well‐characterized samples. The strategy of FM‐TDS is sample excitation by a fast linear frequency sweep, whose autocorrelation function is mathematically equivalent to a Dirac delta function. The method permits the fast recovery of high‐quality frequency and impulse‐response information. Impulse responses recovered in the time‐delay domain showed good agreement with a Green’s function model of transient heat conduction. The present work demonstrates that the FM‐TDS measurement strategy yields photothermal information equivalent to that obtainable from a pulsed laser system, with much lower excitation power.

ISSN:0034-6748    

DOI:10.1063/1.1139510

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Frequency‐modulation time‐delay spectrometry (FM‐TDS) was compared with stochastic excitation in photopyroelectric measurements on thin solid samples. These methods involve broadband signal excitation with simultaneous detection of all frequency components within the response bandwidth of the photothermal system. Fast signal recovery was achieved by FFT methods. Both FM‐TDS and wideband random‐noise excitation were found to yield high‐quality, band‐limited impulse‐response information. Random noise measurements were found to be much less susceptible to distortions and nonlinearities in the excitation wave train. FM‐TDS showed superior coherence and signal‐to‐noise ratio (SNR) to random methods. The results of this work demonstrate a photopyroelectric effect spectrometer capable of yielding fast, time‐resolved information equivalent to the response of a pulsed laser, with low peak power. This important feature shows excellent potential for nondestructive thickness, thermal diffusivity, and thermal conductivity measurements on materials which are susceptible to optical damage.

ISSN:0034-6748    

DOI:10.1063/1.1139511

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A method for stabilizing a cw CO2laser using a molecular beam absorption signal as an external reference is described. The laser may be stabilized at line center or at any offset within the Doppler width by Stark tuning the absorption frequency. A time‐domain fractional frequency stability of &sgr;(&tgr;)=2.03×10−10&tgr;−1.3was measured with another CO2laser independently stabilized on the Lamb dip of the 4.3‐&mgr;m fluorescence.

ISSN:0034-6748    

DOI:10.1063/1.1139512

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We report on the use of an optical fiber to measure the refractive index of liquid materials. With a relatively simple detection system, indices can be determined with an average accuracy of ±0.2%.

ISSN:0034-6748    

DOI:10.1063/1.1139513

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Using an optical Kerr shutter and sophisticated automatization procedure, we have shown that it is possible to record routinely, with a good accuracy, and in an experiment consuming a comfortable time, time‐resolved emission spectra of short‐lived species in the time scale of 10 ps and in the spectral range 3900–9000 A˚. This system will allow us to obtain a better understanding of ultrafast dynamics in solution, where time spectral changes provide new insight.

ISSN:0034-6748    

DOI:10.1063/1.1139660

出版商:AIP    

年代:1987

数据来源: AIP