Optimizing the generation of polarization squeezed light in nonlinear optical fibers driven by femtosecond pulses.

Bright squeezed light can be generated in optical fibers utilizing the Kerr effect for ultrashort laser pulses. However, pulse propagation in a fiber is subject to nonconservative effects that deteriorate the squeezing. Here, we analyze two-mode polarization squeezing, which is SU(2)-invariant, robust against technical perturbations, and can be generated in a polarization-maintaining fiber. We perform a rigorous numerical optimization of the process and the pulse parameters using our advanced model of quantum pulse evolution in the fiber that includes various nonconservative effects and real fiber data. Numerical results are consistent with experimental results.

[Safety and efficiency of retrograde intrarenal surgery without X-ray guidance].

INTRODUCTION: The main stages of flexible ureteroscopy in patients with renal stones are usually performed under X-ray guidance. Long-term exposure of ionizing radiation can have negative effects on the patients with nephrolithiasis and the operating team. AIM: To study the results of retrograde intrarenal surgery (RIRS) without fluoroscopic guidance. MATERIALS AND METHODS: The results of flexible ureteroscopy (fURS) without X-ray-guidance in 76 patients were analyzed. There were 46 (53.3%) men and 30 (46.7%) women. The average age was 50.4+/-14.6 years. All patients underwent laboratory tests and non-contrast-enhanced computed tomography to determine the size and density of the stone. In all cases, preoperative ureteral stenting was performed. The average stone size was 10.5+/-4.2 mm. First, ureteroscopy with a rigid endoscope was done to assess the ureter and determine the depth of the introducing ureteral access sheath. After removing the ureteroscope along the guidewire, a ureteral access sheath was put at this distance. An inspection of the collecting system and laser fragmentation of kidney stones were performed using a flexible ureteroscope. In 64 (84.2%) patients, a 4.7 Ch stent was put at the end of the procedure, while in the remaining 12 (15.8%) patients, a ureteral catheter was left for 1-2 days. The operation time, stone-free rate, and the number of intra- and postoperative complications were studied. RESULTS: All fURS were successful and performed without X-ray guidance. The average operation time was 42.5+/-8.0 minutes. After the first session, stone-free rate was 92.1% (70/76). In 6 (7.9%) cases, residual stones were found, which were completely removed after the second session. Intraoperative complications, namely perforation of the upper calyx by the distal end of the ureteral access sheath, were observed in 2 (2.6%) patients, which did not require any additional interventions. Postoperative complications occurred in 10 (13.2%) patients, including fever in 6 (7.9%) and hematuria in 4 (5.3%) cases. There were no serious complications, such as ureteral perforation or sepsis, and no blood transfusion was performed. CONCLUSION: Flexible ureteroscopy with laser lithotripsy can be performed safely and effectively without X-ray guidance.

Coherent amplification of high-power laser radiation in multicore fibers from a rectangular array of cores.

The coherent propagation and amplification of high-power laser radiation in a multicore fiber consisting of a square array of weakly bound cores are studied. Exact stable analytical solutions are found for the out-of-phase mode, which describes the coherent propagation of wave beams in such fibers. The analytical results are confirmed by direct numerical simulation of the wave equation. The stability conditions of the out-of-phase mode in the active medium are found.

Coherent propagation and amplification of intense laser pulses in hexagonal multicore fibers.

Propagation and amplification of intense coherent laser pulses in a multicore fiber of 24 weakly coupled cores arranged in the form of seven close-packed hexagons were studied. Exact stable analytical solutions are found for the out-of-phase mode, which describes the coherent propagation of wave beams and temporal soliton solutions in such fibers. Their stability is demonstrated. The analytical results are confirmed by the direct numerical simulation of the wave equation.

Laser pulse compression up to few-cycle durations in multicore fiber.

A mechanism for self-compression of laser pulses in a multicore fiber on the basis of nonlinear combining of radiation from many cores, surrounding the central core in a ring and its trapping into the central core in a chirp-free and pedestal-free soliton-like pulse, is proposed. It is shown that the compression ratio is weakly dependent on the energy and the number of cores in the fiber and approximately equal to 6 with an almost 100% energy efficiency. The compression ratio can be increased to 40 with an efficiency of more than 50% by using additional compression of longer pulses with approximately the same energy. The possibility of a 38-fold compression of a laser pulse to a duration of 15 fs with a pulse energy of 4 nJ in the fiber with realistic parameters was demonstrated numerically.

High-energy femtosecond pulse shaping, compression, and contrast enhancement using multicore fiber.

Nonlinear spatiotemporal dynamics of femtosecond pulses in a hexagonal seven-core silica fiber pumped by a sub-µJ 370 fs Er:fiber chirped pulse amplification (CPA) system were studied. Nonlinear pulse shaping and compression in the central core and pedestal coupling to the outer cores were directly measured by frequency-resolved optical gating. Further compression of the pulses spectrally broadened in the multicore fiber down to 53 fs was demonstrated. Two orders of magnitude contrast enhancement of the pulses after compression was observed.

[Eras protocol for laparoscopic Frey procedure (in Russian only)]. / Protokol uskorennogo vosstanovleniia bol'nykh pri laparoskopicheskoi operatsii Freia.

AIM: To assess the use of ERAS in laparoscopic Frey procedure. MATERIAL AND METHODS: From August 2012 to November 2017 laparoscopic Frey procedure were performed in 35 patients. Fully laparoscopic were performed 31 (88.5%) procedures. We use fast-track protocol from 13 patients. We included from statistic analyses patients where procedure was changed or was conversion or was simultaneous procedure. The total number of patients analyzed was 27. The patients were divided into two groups: I - before the fast-track protocol (n=11), II - after the protocol implementation (n=16). RESULTS: The operating time was 460 (365-530) minutes in I group and 420 (295-540) minutes in II group. Blood loss was 150 (5-300) and 150 (40-700) ml. The median postoperative stay period was 10 (5-25) days and 6.5 (3-11) days (p=0.007). CONCLUSION: The combination of laparoscopic technologies and fast-track protocol reduces the duration of the postoperative stay period.

[Laparoscopic pancreatic head resection]. / Laparoskopicheskaia rezektsiia podzheludochnoi zhelezy.

AIM: To analyze the features and efficacy of laparoscopic Frey procedure. MATERIAL AND METHODS: For the period from August 2012 to May 2017 Frey procedure was carried out in 31 patients with chronic calculous pancreatitis Buchler type C. There were 20 men and 11 women aged 48.6±9 years. Mean pancreatic head dimension was 35.5±14 mm, diameter of the main pancreatic duct - 9.6±2.7 mm. RESULTS: Completely laparoscopic procedure was made in 28 (90.3%) cases. One patient required intraoperatively Beger's technique without conversion. The last was need in 2 (6.5%) cases. Time of surgery and blood loss were 447.3±90.4 min and 215±177.7 ml respectively. Mean postoperative hospital-stay was 8.4±4.5 days. Postoperative complications occurred in 7 patients. Mortality was absent. Follow-up was 1-41 months. Recurrent pain syndrome was observed in 1 case. However, it was less severe and does not require analgesia.

Toward a mid-infrared femtosecond laser system with suspended-core tungstate-tellurite glass fibers.

A simple design of a fiber laser system for generating high-quality pulses with a duration of order 100 fs with ultrabroad wavelength tunability in the 2-5 µm range is discussed. This design incorporates conventional fs near-IR lasers and specially developed tungstate-tellurite fibers with two zero-dispersion wavelengths (ZDW) and relies on nonlinear wavelength conversion via either soliton self-frequency shift (SSFS) or red-shifted dispersive wave (DW) generation. The fiber parameters needed for such optical conversion have been scanned numerically and showed a possibility of SSFS beyond 4 µm and of DW generation beyond 5 µm. We have also studied and prepared tungstate-tellurite glasses and preforms that are highly stable against crystallization, exhibit extremely low level of hydroxyl groups absorption, and from which the suspended-core two-ZDW fibers can be manufactured.

Shaping of cylindrical and 3D ellipsoidal beams for electron photoinjector laser drivers.

With the use of spatial light modulators it became possible to implement in experiments the method of controlling the space-time intensity distribution of femtosecond laser pulses stretched to picosecond duration. Cylindrical and quasi-ellipsoidal intensity distributions were obtained and characterized by means of a 2D spectrograph and a cross-correlator.

[Duodenal dystrophy: An interdisciplinary problem].

Duodenal dystrophy (DD) is the pathological change in the wall of the duodenum, which is caused by chronic inflammation in its ectopic pancreatic tissue. The most common complications of DD are acute or chronic pancreatitis and impaired duodenal patency, which along with severe pain are an indication for surgical treatment. Pancreaticoduodenal resection is recognized as the operation of choice. The paper describes a clinical case demonstrating the efficiency and safety of minimally invasive (laparoscopic) surgical technologies in this category of patients. Resectional interventions of this volume are also shown to be accompanied by the development of pancreatic insufficiency that necessitates continuous enzyme replacement therapy.

Disk Yb:KGW amplifier of profiled pulses of laser driver for electron photoinjector.

We investigated a diode-pumped multipass disk Yb:KGW amplifier intended for amplifying a train of 3D ellipsoidal pulses of a laser driver for a photocathode of a linear electron accelerator. The multipass amplification geometry permitted increasing the energy of broadband (about 10 nm) pulses with a repetition rate of 1 MHz from 0.12 µJ to 39 µJ, despite large losses (two orders of magnitude) introduced by a beam shaper of 3D ellipsoidal beam. The distortions of the pulse train envelope were minimal due to optimal delay between the moment of pump switching on and arrival of the first pulse of the train.

Widely tunable mid-infrared fiber laser source based on soliton self-frequency shift in microstructured tellurite fiber.

A turnkey fiber laser source generating high-quality pulses with a spectral sech shape and Fourier transform-limited duration of order 100 fs widely tunable in the 1.6-2.65 µm range is presented. It is based on Raman soliton self-frequency shifting in the suspended-core microstructured TeO2-WO3-La2O3 glass fiber pumped by a hybrid Er/Tm fiber system. Detailed experimental and theoretical studies, which are in a very good agreement, of nonlinear pulse dynamics in the tellurite fiber with carefully measured and calculated parameters are reported. A quantitatively verified numerical model is used to show Raman soliton shift in the range well beyond 3 µm for increased pump energy.

Generating femtosecond optical pulses tunable from 2 to 3 µm with a silica-based all-fiber laser system.

Femtosecond pulses with broad tunability in the range of 2-3 µm are generated in a germanate-glass core silica-glass cladding fiber with a driving pulse at 2 µm produced by an all-fiber laser system consisting of an Er:fiber source at 1.6 µm, a Raman fiber shifter, and a Tm:fiber amplifier. We demonstrate optical pulses with a duration of the order of 100 fs that are the shortest ones reported in the 2.5-3 µm range obtained by fiber laser systems.

Two-color optically synchronized ultrashort pulses from a Tm/Yb-co-doped fiber amplifier.

A method of producing high quality, optically synchronized two-color ultrashort pulses in an active thulium-doped fiber is proposed. We show that sech-shaped femtosecond pulses with essentially different wavelengths can be generated directly from a Tm/Yb-co-doped amplifier: one pulse at about 2 µm and the second pulse with a tunable wavelength up to 2.3 µm, which covers the pump and gain regions of Cr:ZnSe and Cr:ZnS amplifiers. The shortest pulses with durations of 145 fs at 2.25 µm and 125 fs at 2 µm were measured by the FROG (frequency-resolved optical gating) technique.

[A case of favourable outcome of severe acute intoxication with an animal poison after a bite by the monocled cobra].

This paper reports a case of severe acute intoxication with an animal poison after a bite by the monocled cobra. Combined treatment including artificial lung ventilation, infusion-detoxication and desensitizing (hormonal) therapy, hemosorption, correction of metabolic disorders with cytoflavin, antibacterial therapy had positive effect on the patient's condition and ensured the favourable outcome ofpotentially lethal poisoning without the use ofa specific anti-snake venom serum.

Universal Landau pole.

Our understanding of quantum gravity suggests that at the Planck scale the usual geometry loses its meaning. If so, the quest for grand unification in a large non-Abelian group naturally endowed with the property of asymptotic freedom may also lose its motivation. Instead, we propose a unification of all fundamental interactions at the Planck scale in the form of a universal Landau pole, at which all gauge couplings diverge. The Higgs quartic coupling also diverges while the Yukawa couplings vanish. The unification is achieved with the addition of fermions with vector gauge couplings coming in multiplets and with hypercharges identical to those of the standard model. The presence of these particles also prevents the Higgs quartic coupling from becoming negative, thus avoiding the instability (or metastability) of the standard model vacuum.

[Effect of cytoflavin on some physiological values in patients with toxicohypoxic encephalopathy].

The effect of cytoflavin upon bolus intravenous administration on the state of hemodynamic values and liquid sectors of the organism was studied in patients with toxicohypoxic encephalopathy caused by heavy acute poisoning. It is established that the bolus administration of cytoflavin is less effective than dropwise intravenous injection.

[Correction of metabolic disorders during treatment of alcohol-induced liver injuries in patients with acute alcoholic intoxication].

A total of 103 patients with acute alcoholic intoxication were examined and treated for alcohol-induced hepatic lesions. It was shown that remaxol reduced severity of metabolic disorders associated with hypoxic conditions and active lipid peroxidation and thereby decreased the frequency of alcoholic delirium to 10.8% (n=7) compared with ademetionine (10.8%, n=22). Improvement of metabolism resulted in the reduction of stay in the intensive therapy ward by 5.6+/-0.3 and 7.3+/-0.6 days after remaxol and ademetionine therapy respectively). The total duration of treatment decreased by 9.0+/-0.4 and 11.8+/-1.1 days. The use of remaxol reduced the cost of the treatment by 21.7% compared with ademetionine.

[The use of remaxol in combined intensive therapy of acute mushroom poisoning].

A case of very severe mushroom poisoning is reported. Traditional hepatoprotective therapy with ademethionine, ornithine-aspartate, and essential phospholipids failed to ensure positive dynamics of the hepatic and general functional state. Hepatic insufficiency was complicated by cerebral oedema and swelling, bilateral pneumonia, and acute respiratory distress of mixed genesis. Combined therapy with remaxol and ornithine aspartate produced beneficial effect, resulted in the improvement of the patient's condition and favorable outcome of the life-threatening intoxication.