HE RAPIDLY developing field of biophotonics integrates the descriptive and analytical aspects of the life sciences and photonics to register unprecedented achievements in the detection, imaging, identification, kinetics, and manipulation of biological materials. Biophotonics is used in biology to probe formolecular mechanisms,function,andstructure.Inmedicine, biophotonics is used to study tissue and blood at the macroand micro-organism level to detect, diagnose, and treat diseases in ways that are noninvasive or minimally invasive to the body. Applications of biophotonics include using light to image or selectively treat tumors, sequence DNA, and identify single biomolecules within cells. Against this backdrop of science and technology, this issue of the IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS (JSTQE) on Biophotonics features articles covering a range of disciplines that describe advances and revolutionary developments in the field. Manuscripts on the latest research and developments in photonics-driven areas such as: bioimaging, biosensors/assays, contrast agents, multicolor probes, biomolecular mechanisms and function, biomolecular structure, advanced medical devices, biocomputers, optical limiters, and biophotonic and biocompatible materials were solicitedforthisJSTQEissue.ThepaperspublishedinthisJSTQE volumerepresenttheimpactofbiophotonicsonnewunderstanding of fundamental biological processes, innovative approaches to major health issues such as novel methods for medical diagnosis and treatment, and new techniques and technologies to satisfy biorelated national security needs such as the detection of toxic agents and pathogens, and associated countermeasures. This issue’s title changed from the prior “Lasers in Medicine and Biology” to the forward-looking “Biophotonics” and is deemed necessary to more properly characterize the rapid and numerous developments that are taking place at the intersection of the life sciences and photonics. The new name subsumes the previous topical areas of the old designation.

We have studied a hydromagnetic wave event in the early noon sector of the cusp region, using HF radar data collected in the southern hemisphere and ground‐based magnetic data from both hemispheres. There were three distinct pulsations, which appear to have been driven by changes in the solar wind, beginning with the passage of a powerful interplanetary shock. This shock triggered the first pulsation, a strong ssc, at 1346 UT. It was followed at 1402 UT by a second pulsation, which had a stable dominant frequency of 3.3 mHz and lasted about half an hour. Although this frequency was close to that of the ssc, the new pulsation was clearly differentiated from the ssc by an abrupt 180° change of phase. A further such phase discontinuity at 1434 UT (near noon MLT) marked the start of a third distinct ULF pulsation with a clearly lower frequency of 2.8 mHz, which continued for another half hour, until 1505 UT, and was correlated with the magnitude of the IMF. These latter two pulsations yielded a successful calibration of the radar observations with ground‐based magnetometer measurements; the pulsation current systems in the northern and southern hemispheres were found to be highly correlated and conjugate. The 3.3‐mHz pulsation was observed over a range of ∼10° in invariant latitude, and its amplitude showed a strong, broad maximum close to the latitude of the cusp as inferred from an independent radar‐satellite analysis of cusp signatures. The zonal E × B motion associated with the pulsation showed a linear latitudinal decrease in phase (25° per degree of latitude) while the meridional motion had nearly constant phase. The longitudinal phase variation corresponded to an m value of ∼10 with a source at later MLT. We discuss the possibility that the dominant wave activity near 3 mHz in the latter two pulsations was due to a hydromagnetic surface wave at the magnetopause stimulated by the ssc and modified by the forcing action of the solar wind.

Pulsation events with long (100‐1000 s) periods with a consistent frequency in both particle precipitation and surface geomagnetic field variations have been reported in the past from measurements made at various geomagnetic latitudes. An examination of broad beam riometer and magnetometer data from South Pole Station for the interval from 1982 to 1989 revealed nearly 200 such events. The onset times of these events were determined, and the results compared with predictions based on the work of Coroniti and Kennel (1970). This mechanism ascribes the occurrence of correlated magnetic and precipitation pulsations to ULF modulation of equatorial VLF wave‐particle interactions. For this reason, VLF data from South Pole Station were also examined. Taking into consideration the ULF wave and particle transit times from an interaction region near the magnetic equator to the ground leads to an expectation that the onset of pulsations in the magnetometer data will lag the onset of pulsations in the riometer data by several minutes. This disparity in onset times, together with modulation of VLF emissions in the 0.5‐1 kHz band, serves as an important indicator of whether or not an event can be explained by the above‐cited theory. While about a third of the events fit the prediction of Coroniti and Kennel, another third do not. In these events, the onset of magnetic and precipitation pulsations is nearly simultaneous, and possible alternative generation mechanisms are explored. In the remaining third of the events, magnetic pulsations begin substantially earlier than precipitation pulsations. Events of this type appear at first to be inexplicable in terms of any transit time argument. However, data from the imaging riometer at South Pole Station indicate that this third class of events is probably not physically distinct from the first two but is the result of the differing areas to which the riometer and magnetometer are sensitive and can be accounted for by considering the effects of transverse motion of a persistent precipitation region.

Objectifs, instrumentations et operations de la campagne ballon en Antarctique durant l'ete austral 1985-1986

We are vigorously continuing our research into the design, demonstration, and application of the Nova laser-pumped x-ray laser. Using exploding foil 1,2 plasma amplifier designs we are pursuing inversion schemes using neon, nickel, and other ionization sequences in an effort to achieve significant single-pass or multipass amplification at wavelengths shorter than 10 nm. We report the status of our measurements of the saturation energies, coherent power, beam divergence, modal purity, and other laser characteristics. We also describe our designs and progress on demonstration of multipass amplifiers. Finally, a review is given of the various interesting applications of x-ray lasers having wavelengths in the 3-10-nm regime.

Candidate photopumping materials for resonant photoexcitation x-ray laser schemes were examined to determine spectral line position and radiant line intensity. Improved spectroscopic techniques have permitted several comparative measurements to be made with greater sensitivity and resolution than that of earlier work. A cylindrically focused 0.527-μm laser beam was used to generate the plasma source emission by irradiating thin foil targets. Selected wavelength regions in the 10–17-Å range were studied for possible line coincidences between K-series transitions in F, Ne, and O with emission from transition-metal targets. Within the measurement accuracy of ±2 mÅ, exact spectral line coincidences were found for Mn with the F H-β line at 12.643 Å and for both Mn and Cr with the F He-β line at 14.458 Å. The Mn line at 12.643 has been identified, using ab initio atomic-structure calculations, as the 1D2–1F3 transition in Be-like Mn xxii. This line was found to yield 2–5 mJ into 2π sr with 20 J of laser energy on target. Spectral identifications and wavelengths for Be-like Ti, Cr, Mn, Fe, and Co lines, for Li-like Ti, Cr, and Mn lines, and for N-like Mn lines also resulted from this work.

Accurate wavelengths for highly-ionized L-shell spectra were measured in the 10–16Å region. The purpose being to determine lines in coincidence with L-shell transitions from the elements oxygen, fluorine, and neon. L-shell transitions have been proposed for resonant photopumping of K-shell electrons in these elements to, generate lasing between upper levels in the 40–150 eV region. The current effort improves on and expands the earlier spectroscopic work performed at KMS Fusion, Inc., where possible line coincidences were identified for photoionizing in the 1–3 and 1–4 levels in fluorine. New experimental techniques have led to a wavelength accuracy now believed to be ± 2 mÅ for cases in which adequate calibration lines are available. Exact spectral line matches were found for Mn with the F H,-line at 12.643Å and for both Mn and Cr with the F He line at 14.458Å. The Mn line at 12.643Å has been identified, using ab initio atomic structure calculations, as the 1D2 − 1F3 transition in Be-like Mn XXII. The Mn line emissivity was determined to be 30 MW into 2 steradians for a conversion efficiency of 0.04%. Photopumping with Mn coated gasfilled targets is presently being tried in gain measurement experiments at LLNL.

Information on the location of microburst source regions is limited. One measurement at L ≈ 8.5 placed the source within 4 RE of the ionosphere. Measurements at 5≲ L ≲6, though less conclusive, suggested that source regions may be located either near the equatorial plane or at higher magnetic latitudes along the field line. This paper reports simultaneous observations of bremsstrahlung X rays and VLF radiowave emissions that reveal a detailed correlation between electron microbursts precipitated in one hemisphere and chorus elements of rising frequency recorded at the conjugate point. The measurements were made at Roberval, Canada, and Siple Station, Antarctica (L ≈ 4.1), during magnetic substorms on July 9 and 15, 1975. The relationship between electron energy (50 ≲ E ≲ 200 keV) and wave frequency ( ≲ f ≲4 kHz), and the measured time difference (0.01 s ≤Δt ≤0.13 s) between detection of the electrons and waves at ionospheric conjugate points are consistent with near‐equatorial cyclotron resonance interactions occurring outside the plasmasphere. In both cases, the observations could be accounted for if a diffusive‐equilibrium distribution of electron density along the field line was assumed. The so‐called ‘collisionless’ (or R−4) model of electron density was not in accord with the observations. Some evidence is found for a separation of the wave growth and electron scattering regions. Evidence is also found indicating that the process of electron scattering requires a finite time, up to ∼80 ms under the conditions of these observations. The present results suggest that microburst generation regions are located within 20° of the equator on subauroral field lines.

A balloon payload instrumented with a double‐probe electric field detector and an X ray scintillation counter was launched from Roberval, Quebec, Canada (L =4.1) at 0828 UT (0328 LT) on July 9, 1975. A magnetospheric substorm was observed locally between 0815 and 1100 UT, which produced a maximum ΔB of ∼500 nT at ∼0930 UT. A single‐cell atmospheric thunderstorm developed northeast of Roberval beginning around 0925 UT which was most intense from ∼1000 to 1035 UT. Detailed study of the electrical properties of the thunderstorm, the X ray precipitation data, and VLF spheric data leads to three conclusions. First, the electrical coupling from the thunderstorm to the magnetosphere increases with frequency from dc to the VLF; for the observed storm the amplitude at the ionosphere of thunderstorm produced electric fields was not significant at frequencies below 0.1 Hz. Second, the atmospheric conductivity above the thunderstorm was observed to be about one‐half the fair weather value prior to 1000 UT; decreased to about one‐quarter the fair weather value at about 1000 UT; and remained depressed after the end of the thunderstorm. This result was contrary to that expected on the basis of previous work and is one which merits considerably more investigation. Third, the data show a high probability that half‐hop whistlers initiated by sferics from the thunderstorm triggered energetic electron precipitation from the magnetosphere.

A balloon payload instrumented with thunderstorm dynamics (see Herman and Goldberg, a double-probe electric field detector and an X 1978; Markson, 1978; and references therein). ray scintillation counter was launched from This paper presents electric field, conducti- Roberval, Quebec, Canada (L = 4.1) at 0828 UT vity, and bremsstrahlung X ray data from a (0328 LT) on July 9, 1975. A magnetospheric balloon passing over a thunderstom during a substorm was observed locally between 0815 and magnetospheric substorm. 1100 UT, which produced a maximum AB of 4500 nT Park and Helliwell (1971) suggested that at 40930 UT. A single-cell atmospheric thunder- thunderstorm electric fields may produce a local storm developed northeast of Roberval beginning enhancement of the thermal electron density which around 0925 UT which was most intense from 41000 could increase the refractive index along a to 1035 UT. Detailed study of the electrical geomagnetic flux tube so as to channel VLF properties of the thunderstorm, the X ray radiation into a particular magnetospheric dut precipitation data, and VLF spheric data leads to (Helliwell, 1965; Strangeways, 1978; Strangeways three conclusions. First, the electrical and Rycroft, 1979). Subsequent calculations of coupling from the thunderstorm to the magnetos- the propagation of these fields to the ionosphere phere increases with frequency from dc to the have supported the model (Park and Dejnakarintra, VLF; for the observed storm the amplitude at the 1973). ionosphere of thunderstorm produced electric The propagation of ac electric fields through fields was not significant at frequencies below the atmosphere to the ionosphere hah, tudied 0.1 Hz. Second, the atmospheric conductivity to some extent in the ULF band, < 3 Hz (Bostrm above the thunderstorm was observed to be about et al., 1973; Dejnakarintra and ParR, 1974; one-half the fair weather value prior to 1000 UT; Greifinger and Greifinger, 1976). These studies decreased to about one-quarter the fair weather suggest that thunderstorm-generated ULF noise may value at about 1000 UT; and remained depressed contribute to the ULF noise level in the after the end of the thunderstorm. This result magnetosphere. At higher frequencies, in the VLF was contrary to that expected on the basis of band, 3-30 kHz, electromagnetic radiation from previous work and is one which merits con- lightning discharges is an important source of siderably more investigation. Third, the data natural whistler mode emissions in the magnetos- show a high probability that half-hop whistlers phere (Helliwell, 1965). However, a model to initiated by sferics from the thunderstorm describe in detail the penetration of VLF triggered energetic electron precipitation from radiation through the ionosphere has not been the magnetosphere.

Proton-induced sulfur $\mathrm{LMM}$ and carbon $\mathrm{KLL}$ Auger yields from S${\mathrm{F}}_{6}$, C${\mathrm{F}}_{4}$, and C${\mathrm{Cl}}_{4}$ gaseous targets are found to be substantially reduced from the corresponding yields observed using ${\mathrm{H}}_{2}$S, S${\mathrm{O}}_{2}$, and C${\mathrm{H}}_{4}$. Speculations about the observed dependence on chemical species include inelastic scattering of the Auger electron during its transit out of the molecule and double Auger emission to the continuum.

Intense electron microbursts were detected by means of bremsstrahlung X ray measurements during a period of strong substorm activity on July 31, 1973. The time resolution of the X ray data was sufficient to examine in detail the temporal and spectral features of individual microbursts in differential energy windows of 25–50, 50–75, and 75–100 keV. The duration (full width at half maximum) of a typical microburst was ∼150 ms; periodic spacings in multiple microbursts were of the order of 0.5 s. Both of these characteristic times are at the low end of the range of corresponding times observed for microbursts at higher latitudes. With respect to the mean spacing in multiple microbursts, this result is consistent with precipitation models which predict an L dependence for this characteristic time. Power spectra of long segments of data showed that the microbursts tended to cluster in groups spaced from 3 to 7 s apart. Significant substructure of the order of 30–70 ms was evident in many microbursts. Double-peaked bursts were frequently observed in the 75- to 100-keV channel. Microbursts exhibiting substantially different rise times, of the order of 30 and 70 ms, could also be distinguished in the 75- to 100-keV channel.

High-resolution x-ray spectral measurements are used to determine the relative intensity of x-ray transitions for ions such as fluorine excited in collisions with various-pressure Ne, Ar, and Kr gas targets, thin carbon foils, and a thick carbon slab. The relative intensities are observed to be nonlinearly dependent on both target density and incident charge $Z$. These effects are attributed to strong collisional quenching of initial states by subsequent large-impact-parameter collisions. The data permit extraction of the total quenching cross sections (${\ensuremath{\sigma}}_{Q}$) for fast fluorine ions in various states. A strong enhancement of the relative intensity of $2^{3}P_{1}$ is observed for ${\mathrm{F}}^{7+}$ and ${\mathrm{O}}^{6+}$ projectiles. This strong enhancement is attributed to selective excitation of metastable states in the beam, i.e., $1s2s^{3}S_{1}$, into the $1s2p^{3}P_{1}$ state. Finally, the data for foil and solid targets are used to obtain information on the excitation states of ions moving in solids.