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.

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.

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.

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.

Generating tunable optical pulses over the ultrabroad range of 1.6-2.5 µm in GeO2-doped silica fibers with an Er:fiber laser source.

We report generation of femtosecond optical pulses tunable in the 1.6-2.5 µm range using GeO2-doped core silica-cladding fibers. Optical solitons with a duration of 80-160 fs have been measured by the FROG technique in the 2-2.3 µm range. To the best of our knowledge, these are the longest wavelength temporally characterized solitons generated in silica-based fibers. We have also demonstrated more than octave-spanning femtosecond supercontinuum generation in the 1.0-2.6 µm range.

All-fiber design of erbium-doped laser system for tunable two-cycle pulse generation.

We report a simple all-fiber design of an Er-doped laser system that is capable of generating widely tunable two-cycle pulses. In particular, 13-fs pulses at a wavelength of 1.7 µm are produced. The mechanism of pulse shortening is identical to the higher-order soliton compression and is supported by modeling based on the slowly evolving wave approximation, which is well suited for down to single-cycle pulse propagation in nonlinear dispersion-shifted fibers.

Dual-band Tm3+-doped tellurite fiber amplifier and laser at 1.9 µm and 2.3 µm.

Ultrabroadband amplification and two-color CW lasing simultaneously near 1.9 µm and 2.3 µm in a Tm3+-doped tellurite fiber were demonstrated experimentally, for the first time to the best of our knowledge. A low-loss Tm3+-doped core fiber from TeO2-ZnO-La2O3-Na2O glasses stable against crystallization was produced by a special technique, providing a low concentration of hydroxyl groups. Supercontinuum from a highly GeO2 doped silica fiber pumped by an Er fiber laser system was used as a seed for an amplifier. A maximum gain of 30 dB and 7 dB was measured at 1.9 µm and 2.3 µm, respectively. We report detailed experimental and theoretical studies, which are in a very good agreement, of laser amplification and generation in the manufactured fiber with carefully measured and calculated parameters. A quantitatively verified numerical model was used to predict power scalability at 2.3 µm in schemes with optimized parameters at increased pump power. The presented results show that a high-quality tellurite fiber is a promising candidate for developing lasers in the 2.3 µm atmospheric window which are particularly relevant for applications in gas sensing, eye-safe laser radars, breath analysis, remote sensing and stand-off trace gas detection.

III-nitride tunable cup-cavities supporting quasi whispering gallery modes from ultraviolet to infrared.

Rapidly developing nanophotonics needs microresonators for different spectral ranges, formed by chip-compatible technologies. In addition, the tunable ones are much in demand. Here, we present site-controlled III-nitride monocrystal cup-cavities grown by molecular beam epitaxy. The cup-cavities can operate from ultraviolet to near-infrared, supporting quasi whispering gallery modes up to room temperature. Besides, their energies are identical in large 'ripened' crystals. In these cavities, the refractive index variation near an absorption edge causes the remarkable effect of mode switching, which is accompanied by the spatial redistribution of electric field intensity with concentration of light into a subwavelength volume. Our results shed light on the mode behavior in semiconductor cavities and open the way for single-growth-run manufacturing the devices comprising an active region and a cavity with tunable mode frequencies.

[Ogilvie's syndrome]. / Sindrom Ogilvi.

In the last 5 years the authors had 10 patients with Ogilvie's syndrome under observation. The frequency of the development of the syndrome among all patients who were in the department in this period of time was 0.09%, those who underwent operation accounted for 0.1%. Mortality was 60%. Seven patients were treated by operation. In all patients the syndrome developed in a severe internal disease of an operative intervention. The authors encountered the following clinical diagnostic signs in these patients: moistened tongue, mild tachycardia, absence of hypertrophy of the intestinal wall, and no fecal masses found in the lumen of the large intestine on operation.

[Intensification of surgical activities in the department of general surgery]. / Intensifikatsiia khirurgicheskoi raboty v obshchekhirurgicheskom otdelenii.

The authors intensified and improved considerably the qualitative indices of surgical activity in a department of general surgery by means of simple and practicable organizational measures and by changing the tactics of surgical management of some diseases. This allowed the conclusion that the number of beds in the department must be reduced by 15 without reduction of the staff, which will not affect the activity of the department unfavourably. The organization of a resuscitation department without additional expenses is planned at the cost of the measures mentioned above.