Momentum-Space Observation of Optically Excited Nonthermal Electrons in Graphene with Persistent Pseudospin Polarization.

The unique optical properties of graphene, with broadband absorption and ultrafast response, make it a critical component of optoelectronic and spintronic devices. Using time-resolved momentum microscopy with high data rate and high dynamic range, we report momentum-space measurements of electrons promoted to the graphene conduction band with visible light and their subsequent relaxation. We observe a pronounced nonthermal distribution of nascent photoexcited electrons with lattice pseudospin polarization in remarkable agreement with results of simple tight-binding theory. By varying the excitation fluence, we vary the relative importance of electron-electron vs electron-phonon scattering in the relaxation of the initial distribution. Increasing the excitation fluence results in increased noncollinear electron-electron scattering and reduced pseudospin polarization, although up-scattered electrons retain a degree of polarization. These detailed momentum-resolved electron dynamics in graphene demonstrate the capabilities of high-performance time-resolved momentum microscopy in the study of 2D materials and can inform the design of graphene devices.

Laser cooling without spontaneous emission.

This Letter reports the demonstration of laser cooling without spontaneous emission, and thereby addresses a significant controversy. It works by restricting the atom-light interaction to a time short compared to a cycle of absorption followed by natural decay. It is achieved by using the bichromatic force on an atomic transition with a relatively long excited state lifetime and a relatively short cooling time so that spontaneous emission effects are minimized. The observed width of the one-dimensional velocity distribution is reduced by ×2 thereby reducing the "temperature" by ×4. Moreover, our results comprise a compression in phase space because the spatial expansion of the atomic sample is limited. This accomplishment is of interest to direct laser cooling of molecules or in experiments where working space or time is limited.

Peyronie's disease among men who have sex with men: characteristics, treatment, and psychosocial factors.

INTRODUCTION: We describe the characteristics of Peyronie's disease (PD) and its associated psychosocial implications in men who have sex with men (MSM). AIM: The aims of this article are to identify presenting characteristics and treatment for MSM with PD, compare these findings to non-MSM PD patients, and determine the psychosocial impact of PD among MSM. MAIN OUTCOME MEASURES: Subjective and objective presenting characteristics, MSM psychosocial factors. METHODS: We identified 27 MSM with PD presenting from 2000 to 2012 through a retrospective chart review. A random selection of 200 non-MSM PD patients was identified, who presented during the same time period. A prospective nonvalidated questionnaire was given to MSM PD patients for evaluation of psychosocial constructs. RESULTS: A traumatic event leading to activation of PD was identified equally among MSM and non-MSM (P = 0.815). Most common recognized activators of PD among MSM were: penetrative sexual intercourse (22.2%), self-stimulation (11.1%). More MSM presented with the primary complaint of penile deformity, including narrowing, indentation, hourglass, and hinge (11.1% MSM vs. 1.0% non-MSM, P = 0.01). No differences in total curvature, erection grade were found (P > 0.05). PD had a negative effect on emotional status (89.0% MSM, 80.5% non-MSM, P > 0.05) and intimate relationships (45.0% MSM, 64.0% non-MSM, P > 0.05). Nonsurgical treatment was given to 88.9% MSM and 76.5% non-MSM (P > 0.05), and corrective surgery in 29.6% MSM and 25.0% non-MSM (P > 0.05). Of the 75.0% of MSM engaging in anal sex, 41.7% reported penetrative anal intercourse as the activator of PD. Among MSM, 31.3% experienced decreased libido, 50.0% decreased frequency of sexual activity, 92.9% were self-conscious about the appearance of their penis, and 92.9% were dissatisfied with the size of their penis. CONCLUSIONS: Few differences exist in the clinical presentation and treatments used between MSM and non-MSM PD patients. There was evidence of emotional distress in both groups. As a result, psychosexual assessment and treatment, when indicated, should be considered essential to the patient presenting with PD.

Peyronie's disease plaque calcification--prevalence, time to identification, and development of a new grading classification.

INTRODUCTION: Peyronie's disease (PD) is a connective tissue disorder of the penis in which a fibrous scar in the tunica albuginea can result in multiple penile deformities. AIM: The study aims to investigate the prevalence and time to identification of plaque calcification (PC) in our PD patient population and whether stratification of calcification based on severity seen on ultrasound would serve as a predictor of treatment progression to surgery. METHODS: A retrospective review of 1,041 men presenting with PD from 1993 to 2009 was performed. Eight hundred thirty-four underwent penile duplex ultrasound. MAIN OUTCOME MEASURES: PC was graded as: grade 1 (<0.3 cm), grade 2 (>0.3 cm, <1.5 cm), grade 3 (>1.5 cm; or ≥ 2 plaques >1.0 cm). A matched control group with noncalcified plaques (n = 236) was selected for comparison. RESULTS: Two hundred eighty-four men (34%) were found to have PC noted on ultrasound, and 98 had fully documented dimensions of the PC. Forty-one percent were found to have grade 1, 28% grade 2, and 32% grade 3. When analyzed by grade and progression to surgery, 23% of grade 1, 32% of grade 2, and 55% of grade 3 patients had surgery. Those with grade 3 PC were more likely to undergo surgical intervention for PD (OR 2.28 95% CI 1.07-4.86) and more likely to undergo a grafting procedure than control patients (P < 0.0001). CONCLUSIONS: Men with PC are not more likely to undergo surgery than those without PC (OR 0.95, 95% CI 0.58-1.57). PC is not uncommon, as it was found in 34% of our cohort. PC does not appear to be an indication of mature or stable disease, as it was identified by ultrasound in 37% of patients less than 12 months after onset of symptoms. Men with grade 3 PC have an increased likelihood of progression to surgical intervention and a higher likelihood of undergoing a grafting procedure.

Ultrafast extreme ultraviolet photoemission without space charge.

Time- and Angle-resolved photoelectron spectroscopy from surfaces can be used to record the dynamics of electrons and holes in condensed matter on ultrafast time scales. However, ultrafast photoemission experiments using extreme-ultraviolet (XUV) light have previously been limited by either space-charge effects, low photon flux, or limited tuning range. In this article, we describe XUV photoelectron spectroscopy experiments with up to 5 nA of average sample current using a tunable cavity-enhanced high-harmonic source operating at 88 MHz repetition rate. The source delivers >1011 photons/s in isolated harmonics to the sample over a broad photon energy range from 18 to 37 eV with a spot size of 58 × 100 µm2. From photoelectron spectroscopy data, we place conservative upper limits on the XUV pulse duration and photon energy bandwidth of 93 fs and 65 meV, respectively. The high photocurrent, lack of strong space charge distortions of the photoelectron spectra, and excellent isolation of individual harmonic orders allow us to observe laser-induced modifications of the photoelectron spectra at the 10-4 level, enabling time-resolved XUV photoemission experiments in a qualitatively new regime.

High-power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools.

We present a detailed description of the design, construction, and performance of high-power ultrafast Yb:fiber laser frequency combs in operation in our laboratory. We discuss two such laser systems: an 87 MHz, 9 W, 85 fs laser operating at 1060 nm and an 87 MHz, 80 W, 155 fs laser operating at 1035 nm. Both are constructed using low-cost, commercially available components, and can be assembled using only basic tools for cleaving and splicing single-mode fibers. We describe practical methods for achieving and characterizing low-noise single-pulse operation and long-term stability from Yb:fiber oscillators based on nonlinear polarization evolution. Stabilization of the combs using a variety of transducers, including a new method for tuning the carrier-envelope offset frequency, is discussed. High average power is achieved through chirped-pulse amplification in simple fiber amplifiers based on double-clad photonic crystal fibers. We describe the use of these combs in several applications, including ultrasensitive femtosecond time-resolved spectroscopy and cavity-enhanced high-order harmonic generation.