10 GHz pulse repetition rate Er:Yb:glass laser modelocked with quantum dot semiconductor saturable absorber mirror.

Semiconductor saturable absorber mirror (SESAM) modelocked high pulse repetition rate (≥10 GHz) diode-pumped solid-state lasers are proven as an enabling technology for high data rate coherent communication systems owing to their low noise and high pulse-to-pulse optical phase-coherence. Compared to quantum well, quantum dot (QD)-based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the first 10 GHz pulse repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting 2 ps pulse width from an Er-doped glass oscillator (ERGO). The 10 GHz ERGO laser is modelocked with InAs/GaAs QD-SESAM with saturation fluence as low as 9 µJ/cm2.

Green-diode-pumped femtosecond Ti:Sapphire laser with up to 450 mW average power.

We investigate power-scaling of green-diode-pumped Ti:Sapphire lasers in continuous-wave (CW) and mode-locked operation. In a first configuration with a total pump power of up to 2 W incident onto the crystal, we achieved a CW power of up to 440 mW and self-starting mode-locking with up to 200 mW average power in 68-fs pulses using semiconductor saturable absorber mirror (SESAM) as saturable absorber. In a second configuration with up to 3 W of pump power incident onto the crystal, we achieved up to 650 mW in CW operation and up to 450 mW in 58-fs pulses using Kerr-lens mode-locking (KLM). The shortest pulse duration was 39 fs, which was achieved at 350 mW average power using KLM. The mode-locked laser generates a pulse train at repetition rates around 400 MHz. No complex cooling system is required: neither the SESAM nor the Ti:Sapphire crystal is actively cooled, only air cooling is applied to the pump diodes using a small fan. Because of mass production for laser displays, we expect that prices for green laser diodes will become very favorable in the near future, opening the door for low-cost Ti:Sapphire lasers. This will be highly attractive for potential mass applications such as biomedical imaging and sensing.

Low repetition rate SESAM modelocked VECSEL using an extendable active multipass-cavity approach.

Ultrafast VECSELs are compact pulsed laser sources with more flexibility in the emission wavelength compared to diode-pumped solid-state lasers. Typically, the reduction of the pulse repetition rate is a straightforward method to increase both pulse energy and peak power. However, the relatively short carrier lifetime of semiconductor gain materials of a few nanoseconds sets a lower limit to the repetition rate of passively modelocked VECSELs. This fast gain recovery combined with low pulse repetition rates leads to the buildup of multiple pulses in the cavity. Therefore, we applied an active multipass approach with which demonstrate fundamental modelocking at a repetition rate of 253 MHz with 400 mW average output power in 11.3 ps pulses.

1.55 µm InAs/GaAs quantum dots and high repetition rate quantum dot SESAM mode-locked laser.

High pulse repetition rate (≥ 10 GHz) diode-pumped solid-state lasers, modelocked using semiconductor saturable absorber mirrors (SESAMs) are emerging as an enabling technology for high data rate coherent communication systems owing to their low noise and pulse-to-pulse optical phase-coherence. Quantum dot (QD) based SESAMs offer potential advantages to such laser systems in terms of reduced saturation fluence, broader bandwidth, and wavelength flexibility. Here, we describe the development of an epitaxial process for the realization of high optical quality 1.55 µm In(Ga)As QDs on GaAs substrates, their incorporation into a SESAM, and the realization of the first 10 GHz repetition rate QD-SESAM modelocked laser at 1.55 µm, exhibiting ∼2 ps pulse width from an Er-doped glass oscillator (ERGO). With a high areal dot density and strong light emission, this QD structure is a very promising candidate for many other applications, such as laser diodes, optical amplifiers, non-linear and photonic crystal based devices.

Soliton mode-locked Er:Yb:glass laser.

We report on a simple diode-pumped passively mode-locked Er:Yb:glass laser generating transform-limited 1536-nm solitons of 255-fs duration with a repetition rate of 50 MHz and average power of 58 mW. We also discuss timing jitter and the trade-off between short pulses and high output power in these lasers.

Compact 10-GHz Nd:GdVO4 laser with 0.5-W average output power and low timing jitter.

We demonstrate a compact, diode-pumped Nd:GdVO4 laser with a repetition rate of 9.66 GHz and 0.5-W average output power. The laser is passively mode locked with a semiconductor saturable absorber mirror (SESAM), yielding 12-ps-long sech2-shaped pulses. For synchronization of the pulse train to an external reference clock, the SESAM is mounted on a piezoelectric transducer. With an electronic feedback loop of only a few kilohertz loop bandwidth we achieved a rms timing jitter of 146 fs (integrated from 10 Hz to 10 MHz). This is an upper limit because it is mostly limited by the measurement system. The laser setup with a simple linear cavity has a footprint of only 130 mm x 30 mm.

Optical parametric oscillator with a 10-GHz repetition rate and 100-mW average output power in the spectral region near 1.5 mum.

We demonstrate a synchronously pumped optical parametric oscillator that emits picosecond pulses at an ~1.55-mum wavelength with a repetition rate as a high as 10 GHz and as much as 100 mW of average power. It is pumped with a diode-pumped passively mode-locked 10-GHz Nd:YVO(4) laser. Because of its high repetition rate and its potential for ultrabroad tunability, this kind of system is useful for telecom applications. It should be scalable to 40 GHz and higher as required for future telecom networks.

Picosecond Diode-Pumped Laser System with 9.3-W Average Power and 2.3-mJ Pulse Energy.

We describe a diode-pumped Nd:YAG laser that is suitable for micromachining applications and is capable of generating 2.3-mJ pulses at a 4-kHz pulse repetition frequency. The output pulse duration is 20.5 ps. The system is based on a Nd:YAG regenerative amplifier with a novel four-pass postamplifier. The postamplifier incorporates birefringent depolarization compensation and simultaneously prevents parasitic laser oscillation by use of a nonreciprocal beam path. These output pulse energies are achieved without the use of chirped pulse amplification.

Comparative study of motions in dimethylsulfone by noise excitation and solid echo spectroscopy.

2H NMR spectra of dimethylsulfone were measured with noise excitation and solid echo NMR spectroscopy in the temperature range from 125 to 355 K. Besides the known fact that broad NMR spectra can be measured with both methods, in comparable times it is shown that for noise excitation, the signal loss is negligible compared to echo spectroscopy in the regime when the correlation times of the motions are of the order of magnitude of the echo pulse spacing. For simulating the dynamic NMR spectra acquired with noise excitation, only the motional process must be taken into account and relaxation can be neglected. Furthermore, the problem of restricted acquisition bandwidth in noise NMR spectroscopy is discussed.

Witnessing, wonder, and hope.

This article is based on a keynote address I gave in South Africa at the Eighth International Conference of The South African Association of Marital and Family Therapy. The phenomenon of witnessing is explored in a number of contexts, and a distinction is made between witnessing with and without awareness, and from an empowered or a disempowered position. I propose that the African philosophy of ubuntu--the emphasis of which is on the self in community, in contrast to the Western emphasis on the individual--may be a better fit for my view of hope, which, I propose, is not just a feeling but, rather, something people do.

Conservative management of extra-axial hematomas diagnosed by CT.

Our purpose was to assess the role of serial CT in recently traumatized patients with clinically stable extra-axial intracranial hematomas (EACH) and a midline shift of less than 0.5 cm. A retrospective review of 91 imaging studies in 41 patients (with 45 EACH) was done to assess the time between trauma and CT; the presence and type of skull fracture; the volume, type, and location of the EACH; the presence of associated edema and/or contusion. Over a 19-day follow-up, 11% of the dense EACH increased in volume and 27% decreased. An adjacent skull fracture was seen most frequently in patients with a decrease in EACH volume. Clinical data remain the key to determining the need for neurosurgical intervention in patients with EACH. Follow-up CT afforded no data which altered the medical management of these patients. However, it may be said to have alerted the clinician to an increase in the size of the EACH in 11% of cases, which could mandate close observation of this group.

Diode-pumped passively mode-locked Nd:YAG laser with 10-W average power in a diffraction-limited beam.

We present a passively mode-locked Nd:YAG laser with 10.7-W average output power in a diffraction-limited beam. Stable self-starting mode locking with a pulse duration of 16 ps and a pulse energy of 120 nJ is obtained with a semiconductor saturable-absorber mirror. The laser is directly side pumped with two 20-W diode bars. Single-pass frequency doubling in an external 5-mm-thick KTP crystal yields 3.2-W average power at 532 nm.

Radiologist evaluation of a multispectral image compression algorithm for magnetic resonance images.

With the advent of teleradiology and picture archiving and communication systems (PACS), the expense and time required for image transmission and long term image archiving become important. The use of validated image compression algorithms can greatly reduce these costs. A lossy, multispectral image compression scheme at compression ratios (CR) of 25:1 and 32:1 was used for a set of 26 different patient MR exams. The original and compressed/decompressed (CD) images sets were evaluated in a blinded fashion by four radiologists in two phases. The main objective was to determine whether radiologic interpretation would vary between the two types of CD image sets and the corresponding originals. In general, the compression algorithm caused a slight decrease in image quality; however, the interpretation of pathology did not change between the original and CD image sets. In only one case at the maximum CR = 32 did one of four radiologists change the interpretation of pathology after CD. In this study, lossy multispectral image compression of MR images at CR = 25 maintained diagnostic integrity. This could play a significant role in image storage and communications.

The small and the ordinary: the daily practice of a postmodern narrative therapy.

In this article, I contrast assumptions of a modernist worldview and a postmodern worldview as they relate to clinical practice. Two exercises are described that help therapists develop insight into and practice with the kind of thinking that is consistent with a postmodern narrative clinical practice. Particular attention is paid to the ways that even the small and the ordinary--single words, single gestures, minor asides, trivial actions--can provide opportunities for generating new meanings. Five concepts that I routinely use in my professional and personal life and that are consistent with a postmodern narrative practice--discourse, externalizing the internalized discourse, exceptions, power as the means to produce a consensus, and characteristics of narrative--are illustrated.

IVC filter tilt and asymmetry: comparison of the over-the-wire stainless-steel and titanium Greenfield IVC filters.

PURPOSE: A comparison of tilting, caval coverage, asymmetry, and insertion problems with the over-the-wire stainless-steel and titanium versions of the Greenfield filter. MATERIALS AND METHODS: The study compared 104 stainless-steel and 141 titanium Greenfield inferior vena cava (IVC) filter insertions. The angle the sheath and deployed filter made relative to the cava, as well as filter strut distribution, were determined from spot films. The proportionate caval coverage was computed from the cavogram (anteroposterior projection). Mean filter tilts, subgrouped by insertion site, and caval coverage were compared with the Student t test, whereas strut patterns were analyzed with a contingency table. RESULTS: The filter caval and sheath caval angles correlated. The filter caval angles varied with insertion site, but were lowest with a right jugular approach. Caval coverage was identical with both designs. The stainless-steel version resulted in a more uniform distribution of struts in comparison with the titanium version. The incidence of insertion problems was not significantly different between the filter types. CONCLUSIONS: While IVC filter tilting was not improved with the newer design, the pattern of struts was more uniformly symmetric with the stainless-steel device. The right jugular insertion site was associated with the lowest filter caval angles and the most symmetric pattern of struts.

The neuroimaging features of the cardiolipin antibody syndrome.

The purpose of our study was to define the neuroimaging features of the cardiolipin antibody syndrome. Thirty-eight patients with elevated anticardiolipin antibody titers were studied with magnetic resonance imaging or computed tomography or both. Two patients underwent cerebral angiography. All patients had recurrent transient ischemic attacks, amaurosis, or strokes. One patient had normal imaging findings. The remaining patients had a combination of infarction and atrophy. Focal infarcts, the most common finding, were seen in 32 patients. Cerebral atrophy was seen in 26 patients and was the only radiographic finding in 5. Angiography demonstrated dramatic abnormalities in the distal portions of the anterior and posterior circulations, with multiple stenosis and occlusions and extensive pial and transdural collateral networks. The cardiolipin antibody syndrome should be suspected in young patients with transient ischemic attacks or strokes in the absence of the usual risk factors for cerebrovascular disease. The presence of raised anticardiolipin antibody titers or the cardiolipin antibody syndrome in patients with lupus, in those with other connective tissue diseases, and in patients without overt manifestations of an autoimmune disorder should be viewed as a risk factor for future ischemic cerebrovascular events. Further understanding of the precise role of these antibodies in the pathogenesis of vascular thrombosis may lead to a better understanding of the mechanisms underlying certain forms of stroke.

Diode-pumped passively mode-locked 1.3-microm Nd:YVO(4) and Nd:YLF lasers by use of semiconductor saturable absorbers.

We report on self-starting passively mode-locked diode-pumped 1.3-microm lasers obtained by use of semiconductor saturable absorbers. We achieved pulses as short as 4.6 ps in Nd:YVO(4) and 5.7 ps in Nd:YLF with average output powers of 50 and 130 mW, respectively.