Lloyd L. Steinmetz

Velocimetry of fast surfaces using Fabry–Perot interferometry

This article describes the use of the Fabry–Perot laser interferometer in the fringe mode to measure velocities of fast‐moving reflecting surfaces, and includes a review of previously published work. We begin by describing the theory of the Doppler shift that applies to these situations, and include an experimental test of whether surface normal direction affects Doppler shift. Formulas are derived for the analysis of the effects of shocked, dispersive, moving transparent media on velocity measurements, including expressions for the velocity of light in a moving medium with moving boundaries. The Fabry–Perot method is compared with other techniques such as the VISAR interferometer. We then describe in detail a standard configuration developed at our facilities, discuss other configurations using optical fibers and more than one cylinder lens, and describe a new laser amplifier developed specifically for velocimetry. Methods of alignment, instrument calibration, surface preparation, and operation are inclu...

High-Speed Cell Analysis and Sorting with Flow Systems: Biological Applications and New Approaches

A brief historical account of cell analysis and sorting by high-speed flow-through methods is presented. The status of the Lawrence Livermore Laboratory program in this area is described, including biological applications such as the measurement of the DNA content of mouse liver cells and cultured mammalian cells. Histograms of cellular DNA content can be analyzed mathematically by means of a least squares fitting code. The usefulness of this procedure in extracting information on the life cycle parameters of growing cells is demonstrated. A simple computer model of cell growth is used to demonstrate the accuracy of the fitting code and to elucidate shifts in the shape of the DNA histogram as a function of the fraction of cells in the DNA synthesis phase. A new electronic cell sorter is described with emphasis on new features that insure simplicity, reliability, ease of operation, flexibility, and efficiency. Future directions of both technological development and biomedical applications are considered.

Flow cytometry of DNA in mouse sperm and testis nuclei

Abstract Mutations that occur in spermatogenic cells may be expressed as changes in DNA content, but developmentally-dependent alteration of its staining properties complicates the quantitation fo DNA in individual germ cells. These alterations have been studied with flow cytometric techniques. Nuclei from mouse testis cells and sperm were stained by the acriflavine-Feulgen method. The fluorescence intensity frequency distribution of nuclei of testis cells was characterized by 2 major and 5 minor peaks. Nuclei sorted from the various peaks with a fluorescence-activated cell sorter were identified microscopically. These data were confirmed by generation of peaks with nuclei prepared from cell suspensions enriched in specific cell types. One of the major peaks corresponded to round spermatid nuclei. The other major peak, located at 0.6 of the fluorescence intensity of the round nuclei, corresponded to elongated spermatid nuclei. Purified nuclei of epididymal and vas deferens spermatozoa displayed asymmetric fluorescence distributions. A minor peak at 0.8 the intensity of the round spermatid nuclei was tentatively assigned to elongating spermatids. 2 of the minor peaks, located at 1.7 and 2.0 times the fluorescence intensity of the round nuclei, corresponded to clumps of 2 haploid and diploid nuclei. The additional peaks, located at 3.0 and 3.7 times the fluorescence intensity of round spermatid nuclei correspond to leptotene and zygotene spermatocytes and to late pachytene spermatocytes, respectively. These peaks contained clumps of nuclei. The homogeneity of the nuclei sorted from the peaks, as well as the relative sizes of the peaks, was enhanced when the nuclei were prepared from cells enriched in specific stages of development. The relative fluorescence intensities of the various testis nuclei were characteristic and repeatedly found but were not stoichiometric with the DNA content of the nuclei.

Laser‐Triggered Spark Gap

A laser‐triggered spark gap (LTSG) was developed to meet the need for producing a kilovolt electrical output pulse that is synchronous with the light output pulse of a Q‐switched laser. The LTSG output pulse voltage is variable up to 12 kV, which value makes it usable for actuating Pockel cells. A theoretical explanation of the spark gaps triggering mechanism is developed.

Increased variability in nuclear dna content of testis cells and spermatozoa from mice with irregular meiotic segregation.

Abstract Variability in DNA content to testis cells and sperm from F 1 hybrids between the laboratory mouse ( M. muscullus ) and the tobacco mouse ( M. poschiavinus ), has been determined by flow cytometry (FMC). The F 1 hybrid mouse is known to be heterozygous for seven metacentric chromosomes produced by Robertsonian fusion. Enriched populations of nuclei from late pachytene spermatocytes and round spermatids were obtained by velocity sedimentation. These nuclei, as well as epididymal sperm nuclei and spleen cells, were stained by the acriflavin-Feulgen technique for DNA and measured by FCM. Peaks in the fluorescence intensity frequency distributions resulting from these measurements were analyzed to determine their mean fluorescence intensities and their widths (coefficients of variation). Because mean intensities of corresponding cell types from M. musculus and the F 1 hybrids were identical, the average DNA contents were taken to be the same. The average coefficients of variation of the peaks to fluorescence from the pachytene, spermatid, and sperm nuclei and spleen cells from M. muscullus animals were about 5%. While the peaks of fluorescence from spleen cells and pachytene nuclei from f 1 hybrids also had average coefficients of variation of 5%, post-meiotic nuclei from spermatids and spermatozoa had coefficients of variationof 8%. From these results we conclude that, in these F 1 hybrids, abnormal meiotic segregation causes an increased variability of 6% in the amount of DNA in the spermatozoa.

Picosecond photodetector for 257 nm to 1 μm laser pulses

Picasecond temporal response and broad spectral response photodetectors have been fabricated using commercially available diode chips. Improved photoresponse sensitivity is achieved by removing the anode gold contact which obscures the active region. Junction geometry is such that the depletion region is approximately normal to the surface being illuminated, making the device especially useful for fast UV photodetection.

Many-beam velocimeter for fast surfaces

For the past 5 years, we have conceived, built and successfully used a new 10 beam laser velocimeter for monitoring velocity vs time histories of fast moving surfaces, and will have a 20 beam capability soon. We conceived a method to multiplex 5 to 10 beams through a single Fabry-Perot interferometer, without losing any light that our equivalently-performing single beam system could use, and with negligible cross-talk. This saves the cost of 16 interferometers, simplifies operation and takes less space than without multiplexing. We devised special efficient light collecting probes, streak cameras that change sweep speed during the course of the record, and a new double cavity interferometer which is better, cheaper and more flexible than our previous versions. With the 10 recorders, we conceived and employ a method of using both a fast and a slow streak camera on each of 5 beams without reducing the light that is available to either camera separately. Five new galvanometrically-driven triggerable CCD streak cameras will be installed soon.

Striped Fabry-Perots: improved efficiency for velocimetry

Removing a narrow stripe of the reflective coating from the input mirror of a Fabry-Perot interferometer can dramatically increase the amount of light transmitted through the system we have observed gains in excess of 50 when we compare a conventional Fabry-Perot with the striped Fabry-Perot under similar lighting conditions. The stripe affects the distribution of light in the Fabry-Perot peaks causing them to be lower in the center of the pattern. We examine this distribution and discuss its application in analyzing velocities. 1.

Striped double-cavity Fabry-Perot interferometers using both glass and air

We have used piezo-driven Fabry-Perot interferometers in the past for many continuous velocity-time measurements of fast moving surfaces. In order to avoid the annoying drift of some of these devices, we have developed and used inexpensive, solid glass, striped etalons with lengths up to 64 mm. Useable apertures are 35 mm by 80 mm with a finess of 25. A roundabout technique was devised for double cavity operation. We built a passive thermal housing for temperature stability, with tilt and height adjustments. We have also developed and used our first fixed etalon air-spaced cavity with a rotatable glass double-cavity insert. The rotation allows the referee cavity fractional order to be adjusted separately from that of the main cavity. It needs very little thermal protection, and eliminates the need for a roundabout scheme for double cavity operation, but is more costly than the solid glass version. For a cavity with an air length H, glass length T, index n and wavelength (lambda) , the fringe angles are (root)j(lambda) /(H+T/n) where j is the fractional order plus an integer. This means double cavity fringe patterns plotted vs. velocity will cross if both air and glass are part of the system. This crossing, which is an advantage, will not occur for pure glass or pure air systems. The velocity per fringe is given by c(lambda) /4[H+T(n- (lambda) dn/d(lambda) )] where dn/d(lambda) is the derivative of index with respect to wavelengths. This expression therefore includes the effects of dispersion in the glass. Because the angle depends upon T/n and the velocity upon Tn, there is no equivalent air cavity for a given glass cavity. Very high quality glass is preferable to air, since for a given velocity per fringe, the fringe separation is larger for glass cavities, resulting in less finess degradation due to streak camera spatial resolution.