Nonlinear amplification of side-modes in frequency combs.

We investigate how suppressed modes in frequency combs are modified upon frequency doubling and self-phase modulation. We find, both experimentally and by using a simplified model, that these side-modes are amplified relative to the principal comb modes. Whereas frequency doubling increases their relative strength by 6 dB, the growth due to self-phase modulation can be much stronger and generally increases with nonlinear propagation length. Upper limits for this effect are derived in this work. This behavior has implications for high-precision calibration of spectrographs with frequency combs used for example in astronomy. For this application, Fabry-Pérot filter cavities are used to increase the mode spacing to exceed the resolution of the spectrograph. Frequency conversion and/or spectral broadening after non-perfect filtering reamplify the suppressed modes, which can lead to calibration errors.

Optical frequency comb generation from a monolithic microresonator.

Optical frequency combs provide equidistant frequency markers in the infrared, visible and ultraviolet, and can be used to link an unknown optical frequency to a radio or microwave frequency reference. Since their inception, frequency combs have triggered substantial advances in optical frequency metrology and precision measurements and in applications such as broadband laser-based gas sensing and molecular fingerprinting. Early work generated frequency combs by intra-cavity phase modulation; subsequently, frequency combs have been generated using the comb-like mode structure of mode-locked lasers, whose repetition rate and carrier envelope phase can be stabilized. Here we report a substantially different approach to comb generation, in which equally spaced frequency markers are produced by the interaction between a continuous-wave pump laser of a known frequency with the modes of a monolithic ultra-high-Q microresonator via the Kerr nonlinearity. The intrinsically broadband nature of parametric gain makes it possible to generate discrete comb modes over a 500-nm-wide span (approximately 70 THz) around 1,550 nm without relying on any external spectral broadening. Optical-heterodyne-based measurements reveal that cascaded parametric interactions give rise to an optical frequency comb, overcoming passive cavity dispersion. The uniformity of the mode spacing has been verified to within a relative experimental precision of 7.3 x 10(-18). In contrast to femtosecond mode-locked lasers, this work represents a step towards a monolithic optical frequency comb generator, allowing considerable reduction in size, complexity and power consumption. Moreover, the approach can operate at previously unattainable repetition rates, exceeding 100 GHz, which are useful in applications where access to individual comb modes is required, such as optical waveform synthesis, high capacity telecommunications or astrophysical spectrometer calibration.

14 GHz visible supercontinuum generation: calibration sources for astronomical spectrographs.

We report the use of a specially designed tapered photonic crystal fiber to produce a broadband optical spectrum covering the visible spectral range. The pump source is a frequency doubled Yb fiber laser operating at a repetition rate of 14 GHz and emitting sub-5 pJ pulses. We experimentally determine the optimum core diameter and achieve a 235 nm broad spectrum. Numerical simulations are used to identify the underlying mechanisms and explain spectral features. The high repetition rate makes this system a promising candidate for precision calibration of astronomical spectrographs.

Octave-spanning supercontinuum generated in SF6-glass PCF by a 1060 nm mode-locked fibre laser delivering 20 pJ per pulse.

We report the generation of an octave-spanning supercontinuum in SF6-glass photonic crystal fiber using a diode-pumped passively mode-locked fs Yb-fiber laser oscillating at 1060 nm. The pulses (energy up to 500 pJ and duration 60 fs) were launched into a 4 cm length of PCF (core diameter 1.7 microm and zero-dispersion wavelength approximately 1060 nm). Less than 20 pJ of launched pulse energy was sufficient to generate a supercontinuum from 600 nm to 1450 nm, which represents the lowest energy so far reported for generation of an octave-spanning supercontinuum from a 1 microm pump. Since the laser pulse energy scales inversely with the repetition rate, highly compact and efficient sources based on SF6-glass PCF are likely to be especially useful for efficient spectral broadening at high repetition rates (several GHz), such as those needed for the precise calibration of astronomical spectrographs, where a frequency comb spacing >10 GHz is required for the best performance.

Effect of aortic sclerosis on bone mineral measurements by dual-photon absorptiometry.

Measurements of the bone mineral content (BMC) of lumbar spine by dual-photon absorptiometry (DPA) are performed mainly in the anteroposterior (AP) projection. Due to superimposition of the abdominal aorta, the BMC measured for patients with aortic calcification usually is too high. To determine the influence of aortic calcifications, DPA scans were performed in the AP-projection on 100 dissected abdominal aortae with different degrees of atherosclerosis placed on a human lumbar spine cast in lucite. The measured values were compared with those obtained in the same projection without the aortae. The average increase of the BMC values relative to the mean for the vertebrae L2 to L4 for aortae with severe complicated lesions, i.e., those containing larger amounts of calcium, was 0.03 g/cm2, with a maximum deviation of 0.09 g/cm2. Aortae with fatty streaks or fibrous plaques did not cause significant increases of the BMC. The mean deviation for aortae with mild complicated lesions, i.e., those containing smaller amounts of calcium, was within the range of instrument precision.

An embryo transfer study of reciprocal cross differences in growth and carcass traits of Duroc and Landrace pigs.

Reciprocal cross differences have been reported for growth rate and carcass traits in F1 pigs with the Duroc (D) as a parent breed. Such differences are synonymous with maternal effects if effects of sex linkage and genomic imprinting are negligible. In the present study, transfer of embryos (ET) to paternal breed recipients partitioned effects occurring at or before fertilization from postfertilization effects for growth and carcass traits in F1 D-Landrace (L) pigs. Fifteen boars sired 115 F1 litters, 49 produced by ET. Growth rate of 349 barrows and 361 gilts and carcass measurements on 256 barrows and 159 gilts were analyzed assuming mixed linear models with animal and litter as random effects. Contrasts among genotype (D x L, L x D)- treatment (ET, non-ET) means were tested. Reciprocal cross differences were not detected for growth rate or for carcass weight, length, average backfat thickness, estimated carcass lean, or lean per day of age. Reciprocal cross differences for 10th rib backfat thickness (BF) and longissimus muscle area (LMA) were detected only in barrows. The sexual dichotomy for reciprocal cross differences followed expectations for a Y-linked gene(s), consistent with the fact that reciprocal D-L crossbred barrows exhibited a paternal effect, with responses more like the sire breed than the dam breed. Barrows that were non-ET from D sires and L dams had 3.9 cm2 larger LMA and 5.8 mm less BF than barrows from L sires and D dams (P less than .001). Barrows from ET sired by D boars had 3.8 cm2 larger LMA than did barrows from ET sired by L boars (P less than .001), although no difference was detected for BF. Barrows sired by D boars reared in a D postfertilization environment (ET) had 6.2 cm2 greater LMA and 4.1 mm less BF (P less than .05) than barrows sired by L boars gestated and reared by D dams (non-ET). Barrows sired by D boars reared by L dams (non-ET) had 1.5 cm2 greater LMA and 2.3 mm less BF (P greater than .10) than barrows sired by L boars reared by L dams (ET). In conclusion, reciprocal cross differences detected for BF and LMA in barrows were established before or at fertilization and seemed to be Y-linked.

The history of the Nederlandse Vereniging voor Hypnose (Netherlands Society of Hypnosis).

The foundation and history of the Nederlandse Vereniging voor Hypnose (Netherlands Society of Hypnosis or Nvvh) is described. The year 2001 marks the 70th anniversary of the Nvvh's creation. The article describes the accomplishments, leadership, and philosophy of the Society across the decades. Current professional and training directions are discussed.

[Vaginal sonography in the diagnosis of early pregnancy]. / Vaginosonographie zur Diagnostik der frühen Schwangerschaft.

In this study is reported on 401 transvaginal sonographic examinations in first trimenon of pregnancy. There were interpreted biometrical and functional findings. With 5 weeks p.m., chorion cavity can be identified by a transvaginal scan probe reaching a diameter of 3-8 mm. The vital embryo is recognized by its cardiac action with a embryonic length of 3 mm at the end of 6 weeks post menstruation. Thus with transvaginal sonography, details of embryonic development in the first trimester are visible 1-2 weeks earlier than with abdominal ultrasound examination. It is possible to estimate embryonic and trophoblastic structures of early gestation and to recognize non-viable early pregnancies.

The follicular phase stimulated by human pituitary gonadotropin and the luteal phase following in vitro fertilization.

The pattern of follicular and luteal phase levels of serum estradiol-17 beta (E2) and progesterone (P) are compared between 5 conception (group P) and 27 nonconception (group N) cycles of patients undergoing in vitro fertilization and embryo transfer. Follicle growth was induced with human pituitary gonadotropin and controlled by daily ovarian ultrasonography measuring the follicular diameters. Group N has significantly (p less than 0.025) higher E2 levels from day -10 up to d-6 as compared with the group P. The day of laparoscopy is designated day 0. In group N the length of E2 phase with E2 levels, exceeding 1.84 nmol/l (500 pg/ml) serum, is greater (p less than 0.001) than in group P 6.9 and 5.6 days, respectively. It is suggested that modifications occur in the endometrium caused by high E2 levels acting for a long time, which disturb the implantation of transferred embryos. No significant differences exist between group N and P, if the diameters of the largest follicle or the mean diameters of the secondary follicles or the number of follicles with a diameter greater than 14 mm are compared. No significant correlations were found between these variables and the E2 levels. A significant correlation (r = 0.85, 14 patients) exists between the E2 rise and the increase of follicular diameters.

[Pregnancies caused by in vitro fertilization in cycles, stimulated with human hypophyseal gonadotropin and chorionic gonadotropin]. / Schwangerschaften durch In-vitro-Fertilisation in Zyklen, stimuliert mit menschlichem hypophysärem Gonadotropin und Choriongonadotropin.

In a program of in vitro fertilization, laparoscopies for oocyte aspiration were performed on 35 patients receiving human pituitary gonadotropin (hPG) and human chorionic gonadotropin (hCG). Of the 122 preovulatory oocytes which were recovered from these patients, 44 (36%) were fertilized and cleaved, and were transferred. 144 immature oocytes were collected, and attempts were made to mature these in vitro. 40 oocytes (28%) could be fertilized and cleaved, and were transferred. Eight pregnancies resulted from 32 embryo transfers (25%), and 22,9% from laparoscopies, respectively. Of the eight pregnancies, there were three preclinical abortions and two clinical abortions, and three patients are well along in the pregnancy. Among the three patients there is one twin pregnancy.

[Development of a method for transuterine gamete transfer--initial results]. / Entwicklung einer Methode zum transuterinen Gametentransfer (GT)--erste Ergebnisse.

A new method for gamete intra fallopian transfer is described by which the tubes can be catheterised via vagina, through the endometrial cavity, in order to place gametes directly to the ampullary portion of the fallopian tube without the need for an operation or anaesthesia. In a first series two clinical pregnancies resulted from 8 transuterine transfers.

[Initial experiences with transvaginal vagino-sonographically controlled follicle aspiration in an in vitro fertilization program]. / Erste Erfahrungen mit der transvaginalen vaginosonographisch gesteuerten Follikelaspiration im IVF-Programm.

From March to May 1987 41 sonographically guided follicular punctures have been performed vaginally. Altogether 208 follicles were aspirated and 149 oocytes (71.7%) could be found. No complications like of bleeding or pelvic inflammatory disease have been observed after puncture. The sonographically guided aspiration technique has proved to possess several advantages in respect of its applicability.