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Abstract
The research and technical achievements in the area of lasers are
summarized every three years by the National Symposium on Laser Technology held
in the Baltic See Resort Swinouj´ scie near Szczecin, Poland. The paper
presents a review´ of the main symposium subjects tracks debated during this
key national laser event in September 2012. There are shown development
tendencies of laser materials and technologies and laser associated branches of
optoelectronics in this country, including the efforts of academia,
governmental institutes, research businesses and industry. The symposium work
are divided to two branches: development of lasers and laser applications,
where the laser systems operators and laser users present their achievements.
Topical tracks of the meeting are presented, as well as the keynote and invited
subjects delivered by key representatives of the laser industry. The STL 2012
was a jubilee meeting held for the Xth time.
Keywords
lasers, laser technology, lasing materials, optoelectronics, laser
theory, laser design, laser components, kinds of lasers, semiconductor lasers,
VCSEL, laser applications, photonics, nonlinear photonics, active optical
fibers, optical fiber lasers, high power lasers, high intensity lasers, laser
atomic clocks
I. INTRODUCTION
EVERY three years the organization
team of then Technical University of Szczecin and now West Pomeranian
University of Technology in Szczecin duly prepares a cyclic National Symposium
on Laser Technology (STL). The 2012 STL was held in Swinouj´ scie near Szczecin
in September.´ The Symposium is intentionally held as a national event to
enable a free exchange of research, technology, construction and application
ideas. Here we present a review of the works presented during this key event of
the local research, technical and application communities of lasers. The works
carried on in this country today concern technology of laser materials,
construction of new lasers and associated equipment as well as laser
applications. Many technical teams participate in laser oriented European
structural and framework projects, sharing and proliferating in this way the
laser associated Intellectual Property. This conference summary paper was also
published in the meeting proceedings.
Laser technology is an important
practical tool, and simultaneously a driving force, of development for many
branches of science, technology, medicine and industry. It embraces: optical
and lasing material technology, laser construction, and laser applications.
Materials are optical, optoelectronic, passive, active, nonlinear, crystals,
semiconductors, glasses, and many more. Laser construction concerns
optimization of existing solutions as well as searching for novel ones. There
are
R. S.
Romaniuk is with Warsaw Univ. of Technology, The Institute of Electronic
Systems (e-mail: rrom@ise.pw.edu.pl).
J. Gajda
is with West Pomeranian Univ. of Technology in Szczecin (e-mail: gajdaj@ps.pl).
Researched materials, components,
laser devices, manufacturing technologies and measurement techniques for laser
parameters. The kinds of researched lasers include: semiconductor, photonic,
gas, ion, solid state including DPSS, free-electron and others. Optical signals
are subject to generation, amplification, synchronization, mixing, frequency
multiplication, up and down conversion, forming into pulse shape, widening,
narrowing, collapsing into solitons, etc. Applications of lasers concern such
areas like: material processing, biology, industry, environment monitoring and
protection, safety, medicine, etc.
Laser technology is intensely developing in this country since the sixties. The first laser was launched/fired in this country in 1969 nearly simultaneously at WAT and PW. The first research teams were formed at Military Academy of Technology WAT (prof. Z. Puzewicz) and at Warsaw University of Technology PW (prof. W. Wolinski), as well as at the Adam´ Mickiewicz University in Poznan (prof. A. Piekara and prof. F.´ Kaczmarek). The domestic research and technical community of laser technology meets since 25 years during the national laser symposia. These symposia are organized traditionally in Swinouj´ scie, under the auspices of Committee of Electronics´ and Telecommunications, Polish Academy of Sciences (PAN), Polish Committee of Optoelectronics, Association of Polish Electrical Engineers, Photonics Society of Poland, by the West Pomeranian University of Technology (formerly Szczecin University of Technology), in cooperation with Military University of Technology and Warsaw University of Technology. The jubilee tenth symposium was organized during the last week of September 2012. The paper contains a debate on chosen topical paths presented by national laser technology centers, University based, Research Institutes, Government Laboratories and Innovative Businesses, in Gdansk, Białystok, Kraków,´ Wrocław, Poznan, Warsaw, Kielce, Gliwice and Torun as well as some others. International cooperation of these communities is emphasized, especially within the large European FP7 research projects on laser technology and photonics. The aim of the conference was to summarize three year achievements of the national laser research community co-financed by the national science agencies and the EU [1]–[67]. The symposium sessions are organized in two major groups of topics: laser theories, simulations and analyses, laser materials, technologies, constructions, laser development; and laser applications from two points of view – by laser constructors and operators and mainly by laser users.
II. OPTICAL FREQUENCY COMBS AND OPTICAL ATOMIC CLOCKS
The OFC (optical frequency comb)
technology is developed in UW-IFT Warsaw and in PWr Wroclaw by laser research
teams using semiconductor lasers and optical fibers. Nonlinear effects are
employed to convert nonlinearly the optical frequency comb from the telecom
band to other bands like to the NIR or fiber telecom region. The combs are
generated using amplitude modulation of a continuous wave laser as well as by a
stabilization of the pulse train generated by a mode locked laser, also by
super-continuum generation by deep self phase modulation in nonlinear photonic
crystal fiber. Combs spanning for more than an octave are used for
ultra-precise measurements of reference phase and frequency. OFC with
controlled base frequency fo and separation (tooth spacing) fr are used for mapping optical
frequencies into the RF. This techniques is used for direct, thus very precise,
measurements of the optical frequencies. Precise optical clock techniques,
using OFC, are applied in measurement systems. An optical frequency is
overlapped with a single tooth of the OFC on a photodiode resulting in a RF
beating signal compared to the RF reference.
Ultimately precise measurement of
time is a foundation for such technologies as broadband communication networks,
GPS navigation, and many more. Optical atomic clock uses electronic transition
frequency in the optical region of the EM spectrum of atoms as a frequency
standard for a particular timekeeping component. Current atomic clocks use,
near absolute zero temperature, atoms slowed down with laser radiation and
probed in atomic fountain (cloud) in a cavity. The most accurate classical
atomic clock, basing on single trapped ions and ultra-cold neutral atoms in
free fall, has the frequency uncertainty 2.3×10−16 which may be transferred to ±1 s per around 140MY. The OFC, which
established a coherent link between optical and RF frequencies, is increasingly
more regarded as a new emerging standard for ultra-precise time definition of
superior precision. Atoms may be trapped in an optical lattice and serve as a
quantum reference. The optical lattice clock shows a line-width one order of
magnitude narrower than that observed for classical atomic clocks with superior
stability.
Optical atomic clock and optical metrology with cold atoms are enablers of new technologies for time reference. To measure time with high accuracy, optical and optical-atom effects are utilized. Optical frequency masters use trapping mechanism. Application of ultra-cold µK atoms allow for ultra-precise spectroscopy and measurement of the frequencies of optical transitions with relative uncertainty of 10−18, thus two orders of magnitude more precise than offered by classical atomic clocks. In other words, the optical frequency of 300 THz is measured with accuracy of mHz. Optical clocks with cold atoms consist of an atomic trap in which a cloud of atoms is controlled in a particular quantum state, cooled down and permanently trapped; ultra-stable laser of the line-width less than 1 Hz to sample the resonant frequencies of the atoms; optical frequency comb for precise measurements of distances between particular components of the spectrum. The work is done at UJ in Krakow in cooperation with UW – Warsaw and UMK – Torun.´
III. ULTRA FAST LASER SCIENCE
Ultra-fast science, strongly combined with laser technology, is the study of physical phenomena that occur on short time scales ranging from picosecond to attoseconds. Short laser pulses are enablers in the study of fundamental mechanisms at this time scale including interactions in matter. Especially interesting are ultrafast interactions and processes in novel materials – ultrafast materials science, but also ultrafast Nano magnetism, atomic and molecular dynamics, light induced chemical reactions, nanoscale and biomolecular imaging. Ultrafast science is inherently associated with short wavelength and high pulse intensity lasers. Attosecond pulses are generated using high harmonic generation (HHG) method and sub optical cycle timescale dynamics. Attoseconds in time are, in turn, associated with femtometers in geometrical dimensions. Femtometers in space and attoseconds in time, in combination with optical atomic clocks, setting very precise phase, time and frequency reference frames, allow to observe not only the intra-molecular chemical processes with great time accuracy and geometric precision but also intra-atomic processes. The dimensions of concern inside a proton are of the order of 0.1 fm.
IV. GRAPHENE AND OTHER LASER
MATERIALS
Graphene,
an allotrope of carbon, paves actively, though not without essential
difficulties, its way in electronics and in photonics applications. Here, among
the national laser scientists, there is an interest in optical properties of
grapheme for applications in optoelectronics, components, optical
communications, laser technology, and photonic integrated circuits. Graphene
exhibits a saturable absorption under strong excitation in the visible and IR.
This effect is used for mode locking in fiber lasers, with graphene based
saturable absorber. Ultrafast response of fiber embedded graphene layer is
tuned electrically. Giant non-linear Kerr coefficient of graphene is a subject
to applied research. Photonic components with propagated solitons are designed
with graphene as a medium. Graphene interaction with the EM field is very
strong which initiates applied research on fiber coupled free graphene
ultra-sensors of the properties of gases and vacuum. Graphene quantum dots of
sub 100 nm radius are researched for optoelectronics components. Recently an
interest was evoked by a silicon analog of graphene – the silicene. Silicene is
manufactured, unlike the graphene, with the aid of laser sputtering and using
the self-organization techniques of individual atoms. This new allotrope form
of silicon is also of interest to laser technology.
The works on graphene applications in laser technology and optoelectronic/photonic components are carried out at Silesian Uni. Technology (T. Pustelny), Wrocław Uni. Technology (K. Abramski), ITME (J. Baranowski, Z. Jankiewicz) and some other places. Graphene is a two dimensional sheet of single layer atoms. Crystalline structure of graphene stems from covalent bonds between C atoms in sp2 hybridization. The sp2 hybridization gives strong and short s bonds in the graphene plane. These bonds are responsible for good mechanical properties of graphene. Apart of s bonds, graphene has resonant p bonds which stem from perpendicular p orbitals to the graphene plane. The p bonds are responsible for electron structure of graphene, thus determine its electrical and optical properties. The valence and conduction bands which are determined by p electrons are degenerated in K points of the Brillouin sphere, which results in zero width of the energy gap. Optical transfers between energy bands are direct. There is a linear dependence between energy of electrons and holes energy on their wave vector. The electrons and holes behave in a relativistic way in graphene. Thus a particular characteristic of the graphene is that the absorption is nondependent on the wavelength, the absorption is constant, from the visible to THz. Graphene is used as a saturable absorber in lasers with self-synchronization of modes. It is expected to be applied as an active matrix in quantum THz generators.
V. QUANTUM CASCADE IR LASERS