Linear fiber laser

Fig. 11.32. (a) Basic principle of fiber ring laser with positive and negative dispersion parts of the fiber (b) linear fiber laser (FR, Faraday rotator FRM, Faraday rotator minor SA, saturable absorber) (c) fully integrated passively mode-locked Nd-fiber laser (CFBG, chirped fiber Bragg grating for dispersion compensation SAM, absorber minor) [11.75]... 

An alternative method for the realization of KLM uses the birefringent properties of the Kerr medium, which turns the plane of polarization of the light wave passing through the Kerr medium. This is illustrated in Fig. 11.23. The incident wave passes through a linear polarizer and is then elliptically polarized by a A/4-plate. The Kerr medium causes a time dependent nonlinear polarization rotation. A A/2-plate and a linear polarizer behind the Ken-medium can be arranged in such a way that the pulse transmission reaches its maximum at the peak of the incident pulse, thus shortening the pulse width [11.55]. This device acts similarly to a passive saturable absorber and is particularly useful for fiber lasers with ultrashort pulses. 

He, X., Fang, X., Liao, C., Wang, D., Sun, J. A tunable and switchable single-longitudinal-mode dual-wavelength fiber laser with a simple linear cavity. Opt Express 17, 21773-21781 (2009)... 

The experiment was carried out by a continuously working Nd YAG-laser fabricated by NEC. The laser has a maximum output of 1200 W and is controlled by handling facility with a linear axle. A stage index fiber optical waveguide with a diameter of d=1000 pm was used for the control of the beam. The focusing optics consist of a focusing lens (f=l 16 mm) and a collimation lens (f=70 mm). 

Linearly polarized, near-diffraction-hmited, mode-locked 1319 and 1064 nm pulse trains are generated in separate dual-head, diode-pumped resonators. Each 2-rod resonator incorporates fiber-coupled diode lasers to end-pump the rods, and features intracavity birefringence compensation. The pulses are stabilized to a 1 GHz bandwidth. Timing jitter is actively controlled to < 150 ps. Models indicate that for the mode-locked pulses, relative timing jitter of 200 ps between the lasers causes <5% reduction in SFG conversion efficiency. 

All of our natural experience with optics occurs in the linear domain. In order to apply nonlinear optics in practice, light must first interact with the NLO material. In our laboratories, free space interconnections are usually employed for this purpose. That is, a laser beam is aimed at the material under examination. In any practical use of NLO, such simplistic solutions will not be possible, for reasons both of safety and rugged construction of the device. Light will need to be moved around in space within the device. In many second order devices, whether they are color-specific lasers, such as doubled diode or YAG lasers, or EO modulators such as spatial light modulators (SLM s) waveguide or fiber optic connections will be used. Aspects of these materials will not be reviewed. 

Most present-day fiber-optic sensors use linear diode arrays combined with optical gratings and measure the absorption, transmission, fluorescence, and reflection in UV, visible, and NIR regions (see Table 3.1). Light travels to the sampling probe via one fiber-optic cable and returns to the instrument via a second. Laser excitation permits long-distance transmission of excitation radiation to get a useful signal from the sample. 

The operation of proximity sensors can be based on a wide range of principles, including capacitance, induction, Hall and magnetic effects variable reluctance, linear variable differential transformer (LVDT), variable resistor mechanical and electromechanical limit switches optical, photoelectric, or fiber-optic sensors laser-based distance, dimension, or thickness sensors air gap sensors ultrasonic and displacement transducers. Their detection ranges vary from micrometers to meters, and their applications include the measurement of position, displacement, proximity, or operational limits in controlling moving components of valves and dampers. Either linear or angular position can be measured ... 

The absolute frequency of the fundamental IS — 2S transition in atomic hydrogen has now been measured to 1.8 parts in 1014, an improvement by a factor of 104 in the past twelve years. This improvement was made possible by a revolutionary new approach to optical frequency metrology with the regularly spaced frequency comb of a mode locked femto-second multiple pulsed laser broadened in a non-linear optical fiber. Optical frequency measurement and coherent mixing experiments have now superseded microwave determination of the 2S Lamb shift and have led to improved values of the fundamental constants, tests of the time variation of the fine structure constant, tests of cosmological variability of the electron-to-proton mass ratio and tests of QED by measurement of g — 2 for the electron and muon. 

Some of the relevant applications of nonlinear optics are currently used in laser technology and fiber communications, such as optical frequency conversion, optical parametric oscillation and amplification, the linear electrooptic effect (Pockels... 

Both single-fiber and multiple-fiber methods are available for determining hair fiber cross-sectional dimensions or changes. Single-fiber methods include linear density, microscope (light or electron), vibrascope, micrometer caliper, and laser beam diffraction. For multiple-fiber determinations, a centrifuge may be used. 

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