A new concept short pulse fiber laser source

Ultrashort-pulse fiber laser systems, which offer, due to their high peak pulse intensity in combination with high pulse frequencies (repetition rate), an innovative technology of nonlinear interaction with materials, help to fabricate components with unprecedented quality, precision and speed. Also due to the short pulse duration, laser energy can be introduced into the material in a shorter time than heat transfer occurs, which thus prevents thermal damage to the part. It is not surprising that industrial laser systems with a sub-nanosecond pulse length are widely used in the markets of precision processing, medical devices and in many other applications. The most critical component of such systems is the seed laser source. To date, the existing devices in the commercial market do not fully satisfy the industrial requirements. In this thesis I describe a new concept for the generation of ultrashort laser pulses using an all-passive, fiber-ring, mode-locked laser with at least two passive spectral filters incorporated. Also presented is a full theoretical model of the operation of the laser. I report on the development and the comprehensive characterization of a fully optimized laser configuration, finding excellent agreement of the theoretical model and the experimental results. Various practical configurations and their application were demonstrated. During the period of the project, a fully commercially developed laser scheme was implemented in a variety of IPG Photonics picosecond and femtosecond laser systems.Open Acces

Suppression of spin-state transition in epitaxially strained LaCoO_{3}

Epitaxial thin films of LaCoO_{3} (E-LCO) exhibit ferromagnetic order with a transition temperature T_c = 85 K, while polycrystalline thin LaCoO_{3} films (P-LCO) remain paramagnetic. The temperature-dependent spin-state structure for both E-LCO and P-LCO was studied by x-ray absorption spectroscopy at the Co L_{2,3} and O K edges. Considerable spectral redistributions over temperature are observed for P-LCO. The spectra for E-LCO, on the other hand, do not show any significant changes for temperatures between 30 K and 450 K at both edges, indicating that the spin state remains constant and that the epitaxial strain inhibits any population of the low-spin (S = 0) state with decreasing temperature. This observation identifies an important prerequisite for ferromagnetism in E-LCO thin films.Comment: 5 pages, 5 figures, submitted to Physical Review

Review of the genus Cassidibracon Quicke, 1987 and related taxa of the Plesiobracon group of genera (Hymenoptera: Braconidae: Braconinae)

Members of several genera of the Plesiobracon genus-group are reclassifed. A new species, Cassidibracon vannoorti sp. n. from South Africa, and two new genera, Isomerosoma gen. n. (type species Bracon subacaudatus Granger, 1949) and Reticulotergus gen. n. (type species Cassidibracon indicus Narendran et Rema, 1994), are described. Pseudochivinia Long et van Achterberg, 2023, stat. n. recently described as a subgenus of Bracon Fabricius, 1804 is considered a valid genus. The genus Triaspidogastra Granger, 1949, syn. n. is synonymised with Esenga Cameron, 1906. The new replacement name Bracon vitobiasi Long et van Achterberg, nom. n. is proposed for the junior primary homonym Bracon tobiasi Long et van Achterberg, 2023 (nec Papp, 1965). The following new combinations are given: Esenga lutea (Granger, 1949), comb. n. (from Triaspidogastra), Esenga testacea (Granger, 1949), comb. n. (from Triaspidogastra), Lyricibracon nigerianus (Quicke, 1988), comb. n. (from Rugosibracon Quicke, 1988), Pseudochivinia vitobiasi (Long et van Achterberg, 2023), comb. n. (from Bracon), Sculptolobus repens (Gupta, 2014), comb. n. (from Cassidibracon Quicke, 1987), Scutibracon gracillariae (Quicke, 2012), comb. n. (from Cassidibracon), Scutibracon malabaricus (Narendran, 1994), comb. n. (from Cassidibracon), Scutibracon sumodani (Narendran et Madhavikutty, 1994), comb. n. (from Cassidibracon), and Trigastrotheca notata (Szépligeti, 1914), comb. n. (from Habrobracon Ashmead, 1895). Lectotypes are designated for Bracon subacaudatus Granger, 1949 and Triaspidogastra lutea Granger, 194

Femtosecond photon echo in dye-doped polymer films at room temperature

The signals of primary and stimulated femtosecond photon echo in polymer films doped with dye (phthalocyanine) molecules have been experimentally investigated at room temperature. A femtosecond echo spectrometer for these echo experiments is described. The decay curves of echo signals with increasing time intervals between excitation femtosecond pulses are obtained and blue shifts of the spectra of femtosecond echo signals with respect to the spectrum of excitation pulses are revealed. The possibilities of using the studied doped polymer films as recording media for high-temperature echo processors and coolants in optical refrigerators are analyzed. © Allerton Press, Inc. 2008

DYNAMIC ECHO-HOLOGRAM TRANSFORMATION IN THREE-LEVEL SYSTEMS.

Dynamic echo holography is a new field where photon (light) echo signals are used. Under certain conditions, information contained in the wave front of excited pulses can be reproduced in the wave front of echo signals. The peculiarities of hologram formation in three-level systems are investigated. Transformation of the real time scale and the events order reversion are possible in stimulated echo hologram recording

Photon echo as a method of a spectroscopy of molecular Iodine vapors in cooling supersonic molecular jets

The article is devoted to photon echo detection in molecular iodine vapors cooled under supersonic jets. This phenomena could be used in spectroscopic diagnosis of the jets. The methodic, results and the possibilities of their practical application in the development of the optical echo-processors are discussed