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The main structure element for generating femtosecond light pulses are lasers. Within two decades after the laser development  the duration of the shortest pulse fall by six orders of magnitude from the nanosecond to the femtosecond regime. Nowadays femtosecond pulses in the range of 10 fs and below can be generated directly from compact and reliable laser oscillators. With the help of some simple comparisons, the incredibly fast femtosecond time scale can be put into perspective. For example, on a logarithmic time scale, one minute is approximately halfway between 10 fs and the age of the universe. Taking the speed of light in vacuum into account, a 10 fs light pulse can be considered as a 3 µm thick slice of light whereas a light pulse of one-second span approximately the distance between earth and moon. It is also useful to realize that the fastest molecular vibrations in nature have an oscillation time of about 10 fs. It is the unique attributes of these light pulses that open up new frontiers both in basic research and for applications. The ultrashort pulse duration, for example, allows freezing the motion of electrons and molecules by making use of pump-probe techniques that work similar to strobe light techniques.
A bandwidth-limited pulse (also called  transform limited pulse) is a pulse of a wave that has the minimum possible duration for a given spectral bandwidth. Optical pulses of this type can be generated mode-locked lasers. Transform-limited pulses have a constant phase across all frequencies making up the pulse. The length of a pulse thereby is determined by its complex spectral components, which include not just their relative intensities, but also the relative positions of these spectral components. For different pulse shapes, the time-bandwidth product is different.
A transform limited laser pulse can only be kept together if the dispersion of the medium the wave is travelling through is zero; otherwise, dispersion management is needed to revert the effects of unwanted spectral phase changes. For example, when an ultrashort laser pulse passes through a block of glass, the glass medium broadens the pulse due to group velocity dispersion.
Ultrafast lasers have been of increasing interest in material processing applications due to their capability of precise micromachining of a large variety of materials: metals, semiconductors, polymers, dielectrics, biological materials, etc.

At the present day, many types of spectroscopic techniques are available to researchers. Standard spectroscopy, such as absorption and emission spectroscopy, is linear and uses one incident light beam. In this case, the observed light interactions have a tendency to be weak and the spectra produced can be indefinite.
Nonlinear spectroscopy, such as Coherent  Raman Scattering and Stimulated Raman Scattering, uses two or more light beams. Many nonlinear spectroscopic techniques can vary the lights optical parameters such as its amplitude, frequency, polarization and phase.
There are several advantages of using nonlinear techniques. Nonlinear spectroscopy uses multiple sources of light, meaning more information is obtained from samples tested using a nonlinear technique.
Nonlinear spectroscopy can be used to study interfacial and surface processes. It can be used to study interactions in areas of the electromagnetic spectrum not accessible to linear spectroscopic methods. Nonlinear spectroscopy is also useful for studying dynamic processes and can be used to understand nanoparticles and their unique optical properties.
Raman spectroscopy provides information about molecular vibrations that can be used for sample identification and quantitation. The technique involves shining a monochromatic light source (i.e. laser) on a sample and detecting the scattered light.
Laser wavelengths ranging from ultraviolet through visible to near infrared can be used for Raman spectroscopy. The choice of laser wavelength has an important impact on experimental capabilities.

1. Sensitivity. For example, an infra-red laser results in a decrease in scattering intensity by a factor of 15 or more, when compared with blue/green visible lasers.
2. Spatial resolution. Thus, the achievable spatial resolution is partially dependent on the choice of the laser.
3. Optimization of resulting based on sample behavior.  For example Blue or green lasers can be good for inorganic materials and resonance Raman experiments and surface-enhanced Raman scattering (SERS). Red or near infra-red (660-830 nm) are good for fluorescence suppression. Ultraviolet lasers for resonance Raman on biomolecules and fluorescence suppression.

Raman spectroscopy is used in many varied fields – in fact, any application where non-destructive, microscopic, chemical analysis and imaging is required.  Whether the goal is qualitative or quantitative data, Raman analysis can provide key information easily and quickly.  It can be used to rapidly characterize the chemical composition and structure of a sample, whether solid, liquid, gas, gel, slurry or powder.

Fiber lasers are used for material processing applications such as cutting and welding in the automotive, manufacturing, heavy industry, and consumer electronic sectors. They are also being used for medical applications. Apart from the mentioned, fiber laser source is used for marking and engraving components for better traceability and for removing product falsification and inventory management. Nowadays, companies have become more careful about the quality of the laser delivered to the process.  The quality of the laser is usually measured on the laser source. Most laser sources will be integrated into a system being used for a specific process, set of processes, or applications. That system can consist of optics and mechanical components used to shape, resize, and deliver the laser energy in many different ways, depending on how the laser is applied. In sum, the laser light from that source can interact with several different components, each having an effect on its quality.
Researchers of market forecast that the global fiber laser market to increase at a CAGR of 15.81% during the period 2016-2020. A new trend in the fiber laser market is the development of ribbon-core fiber laser light source. Researchers have developed ribbon-core fiber lasers to increase the fiber laser output radically while keeping the beam quality. Ribbon-core fiber lasers are produced by a line of doped silica rods surrounded by undoped rods to increase the beam quality. The refractive index of the central ribbon core is high, which helps focus the light. These fiber lasers source can produce high levels of power without getting thermally damaged.
A key market driver is the increased use of fiber lasers in materials processing. The flexibility of using a wide range of materials and the advantages of using lasers over other conventional processes have made them the first choice for many materials processing applications such as metal welding, plastic welding, and brazing mostly in automotive engineering, cladding or repair welding, and cutting of metals for the machine tooling, automobile, and medical sectors. Fiber lasers sources are solid-state and offer high solid-state reliability and convenience. Materials processing involves chemical or mechanical steps for product manufacturing across industries such as automotive, general manufacturing, heavy industry, aerospace, and electronics.

Photonic crystal fibers and fiber lasers are two of the most rapidly developing spheres of optics and photonics over recent years. Photonic crystal fibers are a new class of optical fibers. They have unique artificial like crystal microstructure. They can guide light not only through a common total internal reflection mechanism but with the usage photonic bandgap effect.
The construction of PCFs is flexible. There are several parameters to manipulate: a period of the grating, air hole shape, the refractive index of the glass, and type of grating. Freedom of design permits one to obtain incessantly single mode fibers, which are single mode in all optical range and a cut-off wavelength does not exist. By manipulating the structure it is possible to design required dispersion properties of the fiber. PCFs can be fabricated having zero, low, or anomalous dispersion at visible wavelengths. The dispersion can also be depressed over a large range. Regardless of the type of glass and structure, the usual method of photonic crystal fiber fabrication is multi-rate thinning.
In photonic crystal fiber light is absorbed in the core, providing a better waveguide to photons than standard optical fiber. The polymers used instead of glass in PCF provide the advantage of a more flexible fiber, which provides easier and less expensive installation. Different photonic crystals according to various photonic gratings are produced depending on the required properties of the propagated light.
PCF is finding applications in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission, highly sensitive sensors, and other areas.
Significant features also make photonic crystal fibers very attractive for several specific areas in case of telecom components, quantum optics, the guidance of cold atoms and Bragg fiber.
Photonic crystal fibers mix characteristics of photonic crystals and classical fibers. Research on photonic crystal fibers is still unexplored. Apart from already developed applications as fiber dispersion compensation, supercontinuum generation, and particle guidance is expected a series of new applications in telecommunication, sensing, beam delivery, surgery, spectroscopy, and fiber lasers in the next few years.

Over the last years, the fiber laser technology and its potentials have been sparking the interest laser manufacturers as well as researchers and industrial users. Lasers have an excellent beam quality provided observable advantages and enhancements in high precision and material processing at the micro scale.
Micromachining is concerned with making small characteristic features using such ordinary machining operations as drilling, cutting, scribing, and slotting—but on a smaller scale. There is no official scale to identify when an operation is a micromachining, but a golden rule is that you can to see the results, but without seeing the details.
Up to date laser micromachining techniques are used in the automobile and medical industries, production of semiconductors and solar cell processing. Lasers for micromachining suggest a wide range of wavelengths, pulse width (from femtosecond to microsecond) and repetition frequency (from the single pulse to Megahertz). These values allow micromachining with high resolution in depth and lateral dimensions. The sphere of micromachining consist of manufacturing methods like drilling, cutting, welding, ablation and material surface texturing, where it is possible to attain very fine surface structures ranging in the micrometer.
Nowadays, there is the new innovative micromachining technology including advanced laser markers with superior beam quality. It is being used to achieve results similar to traditional machining technologies, but cheaper, faster, and more flexible.
Recent developments in the use of a fiber laser marker for micromachining can create desired features not normally associated with this equipment. The major benefit of this approach is that fiber laser markers are two to three times less expensive than standard equipment used for micromachining.
The fiber laser micromachining technology can be used for a wide variety of applications, such as selective plating removal for solder barrier, solar cell scribing and hole drilling, hole drilling of stainless steels for medical hypo tubes and fluid flow control systems, and cutting of sub-0.02in.-thick metals for fast part prototyping.

Development of the fiber photosensitivity has opened up new opportunities. The photosensitivity permits fabricating fiber Bragg gratings (FBG), which are now prevalent in many applications such as multiplexers, demultiplexers, and optical add/drop filters, where individual wavelength selection and separation is required.
Fiber Bragg gratings are generated by “inscribing” or “writing” systematic changing of refractive index into the core of a special type of optical fiber using an intense ultraviolet source such as a UV lasers. The type of FBG inscription that is most suitable depends on the type of grating to be manufactured. Generally, a germanium-doped silica fiber is used to inscribe fiber Bragg gratings. The germanium-doped fiber is photosensitive, which means that the refractive index of the core changes with exposure to UV light. The amount of the change depends on the intensity and duration of the exposure as well as the photosensitivity of the fiber.
The methods of FBG inscription consist of two types: holographic (interference) and nonholographic. The first type uses the amplitude or spatial splitting of the beam into two beams, which interfere in the fiber bundle. Nonholographic methods based on the periodic illumination of the fiber with the use of pulsed source through an amplitude mask or point-by-point method.

Interferometer inscription schemes use two-beam interference. Here the UV laser is split into two beams which interfere with each other creating a periodic intensity distribution along the interference pattern. The refractive index of the photosensitive fiber changes according to the intensity of light that it is exposed to. This method allows for quick and easy changes to the Bragg wavelength, which is directly related to the interference period and a function of the incident angle of the laser light.
In the scheme with a Lloyd interferometer (spatial beam splitting), the interference pattern is produced by using a mirror: one-half of the beam is concurred with the other half at the angle. This interferometer comprises a dielectric mirror, which directs half of the UV beam to a fiber that is perpendicular to the mirror.
With a Talbot interferometer by simultaneous rotation of additional mirrors located on rotation stages, wherein the fiber should be placed on a linear stage.This interferometer consists of two plane parallel mirrors and a diffractive element (a phase mask) with its surface aligned perpendicular to the mirrors. The illumination is arranged so as to recombine the first – order beams (or other orders such as the plus first and zero orders) to form the UV interference pattern.
Fiber Bragg gratings inscription using phase mask technique is based on the diffraction of UV light by a mask placed closely to the fiber. The phase mask technique is significantly simpler in comparison with other methods. It has the simple setup and uses low coherence UV laser beam.  
The common method in FBG phase-mask inscription uses dedicated 193nm or 248nm excimer laser models with increased coherence. When illuminated with the laser beam, the phase-mask generates a regular interference pattern. The enhanced spatial coherence length of the excimer laser provides good contrast behind the mask which is typically placed in a distance of 100µm to 200µm from the fiber core.
The phase mask methods quickly have prevailed over other techniques due to simplicity and flexibility of the application and great reproducibility of the inscribed gratings.
Optromix offers unique UV laser Magius SF257 supplied as a part of Fiber Bragg Grating writing workstation. Optromix Company has made it possible to inscribe FBG by all methods, mentioned above.

As an example of an important branch of optics that includes some of disciplines is the field of integrated optics or, in other words, integrated photonics. Integrated photonics is represented by the combining  of waveguide technology with other disciplines, such as electro-optics, acoustooptics, nonlinear optics, and optoelectronics.  

The term “integrated photonics” means the fabrication and integration of several photonic components on a common planar substrate. These components include beam splitting means, gratings, couplers, polarizers, interferometers, sources, and detectors. Along with,then these can  be used as components for fabricating more complex planar devices which can accomplish a different range of functions with applications in optical communication systems, CATV, instrumentation, and sensors.
A photonic integrated circuit (PIC) or integrated optical circuit is a device that includes multiple (at least two) photonic functions and as such is similar to electronic integrated circuit. The major difference between the two is that a photonic integrated circuit provides functions for information signals impressed on optical wavelengths mostly in the visible spectrum or near infrared 850 nm-1650 nm.
The first examples of photonic integrated circuits were 2 section distributed Bragg reflector (DBR) lasers. It was consist of two independently controlled device sections – a gain section and a DBR mirror section. As a result, all modern monolithic tunable lasers, widely tunable lasers, externally modulated lasers and transmitters, integrated receivers, etc. are examples of photonic integrated circuits. The primary application for photonic integrated circuits is in the area of fiber-optic communication through applications in other fields.
The optical multiplexers in wavelength division multiplexed (WDM) fiber-optic communication systems are an example of a photonic integrated circuit. These devices are capable of multiplexing a large number of wavelengths into a single optical fiber, thereby increasing the transmission capacity of optical networks considerably.
The main goal of integrated photonics is the miniaturization of optical systems. It became possible thanks to the small wavelength of the light, which allow the fabrication of photonic devices with sizes of the order of microns. The multiple functions  integration within a planar optical structure  can be achieved by means of planar lithographic production.
The basic concept in an optical integrated circuit is the same as that which operates in optical fiber: the confinement of light. A medium that possesses a certain refractive index, surrounded by media with lower refractive indices,can act as a light trap, where the rays cannot escape from the structure due to the phenomena of total internal reflection at the interfaces.
 

Among the different types of lasers, fiber lasers are the fast-growing and prevalent type of laser due to their meaningful advantages: flexibility, efficiency, and high performance. Most advances in fiber laser technology focused on ytterbium (Yb)-doped fibers operating around 1 micron(µm). Two factors influence the success of these lasers. First, the materials can be very efficient because this materials system has a low quantum defect. Second, there are many high-brightness pump sources at 915–975 nm. These factors allow high-efficiency operation and low thermal loading of the fiber. Nowadays, Yb-doped fiber lasers have been scaled in power to above 3kW with near-diffraction-limited beam quality.
High power single mode fiber lasers at the 1.5-micron wavelength region have the significant advantages of eye safety and enhanced atmospheric transmission. This makes them interesting for a variety of commercial, government, aerospace and defense applications. Er/Yb co-doped fibers pumped at 975 nm (where mature, low-cost diode technology is available) has been the standard method to generate high powers in the 1.5-micron wavelength. Owing to the large quantum defect between the pump and signal wavelengths, the thermal load is significantly enhanced which becomes a limitation for power scaling.
The wavelength range around 2 microns (usually как правило Thulium or Holmium doped) is part of the so-called “eye safe” wavelength region which begins at above 1.4 micron. Laser systems that operate in this region offer exceptional advantages for free space applications compared to conventional systems that operate at shorter wavelengths. This gives them a great market potential for the use of LIDAR and gas sensing systems and for direct optical communication applications. The favorable absorption in water makes such lasers also very useful for medical applications. 2 microns fiber lasers ideal for many surgical procedures.
Optromix Company has  the unique ultraviolet laser at the 0.257 micron based on 4 harmonic. This type of laser found application in the lithographic processing and for FBG inscription. Optromix Company also manufactures green (515-561 nm) and near IR (770-790 nm) fiber lasers based on the second harmonic.
Fiber lasers are useful because they tend to be stable and easy to use, produce high-quality beams, can emit at high powers, and are easy to cool. Placing a suitable gas inside of a hollow optical fiber allowed the researchers to create a fiber gas laser with mid-IR emission between 3.1 and 3.2 microns!Lasers are central to thousands of consumer, industrial and scientific products; the uses for each type of laser depend on factors such as power, beam quality, and wavelength.

In recent times, single frequency lasers with narrow bandwidth have long coherence length and this is an essential property for many applications in industry and science. One of the applications is remote laser sensing and in particularly laser guide star, where high power narrow band width laser at 589nm is required for excitation of sodium atoms. Another important application is coherent beam combining , where the power is scaled up by combining several lasers with the diffraction grating.
The narrow bandwidth (or line width) of a laser, mostly a single-frequency laser, is the width (sometimes used as narrow FWHM) of its optical spectrum. The linewidth of a single frequency laser is the full width at half maximum (FWHM) of the optical spectrum. More precisely, it is the width of the power spectral density of the emitted electric field in terms of frequency, wavenumber or wavelength. The narrow FWHM of a laser is closely related to the temporal coherence. A light field is called coherent when there is a fixed phase relationship between the electric field values at different locations or at different times.It is usually described in terms of the coherence time or coherence length. Phase fluctuations which are restricted to a small interval of phase values provoke a zero linewidth and some noise sidebands. This drifts can also promote to the linewidth and can make it dependent on the measurement time.
This shows that just the narrow band width doesn`t give full information on the spectral purity of laser light. One of the reasons of the noise is the negligent emission of excited atoms and ions. The unpredictable photons have random directions and random phases. Each negligent emission adds a random phase to the optical field. Some radiation arises by the spontaneous emission will amplify very nearly along the same direction as that of the stimulated emission and cannot be separated from it. The main consequence of the spontaneous emission noise is to make the laser output have a finite spectral width.
The spectral bandwidth (linewidth) of single-frequency lasers can be not only broad as several hundreds of megahertz but also narrow as several hundreds of hertz. Typical bandwidths of stable free-running single-frequency lasers are a few kilohertz range, while the linewidths of semiconductor lasers are often in the megahertz range. Much smaller linewidths, sometimes even below 1 Hz, can be reached by stabilization of lasers, which can be achieved using ultrastable reference cavity. Lasers with very narrow linewidth are required for various applications, e.g. as light sources for various kinds of fiber optic sensors, for spectroscopy (e.g. LIDAR), in coherent optical fiber communications, and for atomic trapping and cooling.