Needless to say, evenwith such a 'large' pinhole, all components must be rigidly mounted, andprecisely positioning the pinhole at the exact focus of the laser beamand centering it in X and Y is a non-trivial task!
In this work, we present functionalization of AISI 316L surfaces by nanosecond Nd:YAG laser texturing and adsorption of superhydrophobic fluoroalkylsilane functionalized nano SiO2 particles. Surface modification by tuning the distance between laser-produced micro(μ)-channels lead to different surface roughness. After nanosilica coatings the superhydrophilic laser-textured surfaces are turned into superhydrophobic surfaces with the same μ-roughness. The higher μ-channels density leads to more hydrophobic surfaces after coating. This enable a study of combined effect of surface wettability and morphology on friction coefficient and wear resistance. The experiments were performed in air and water environment. In case of dry friction, increased μ-roughness lead to higher friction coefficient and the water-repellency modification by nanosilica particles has no influence on tribological behavior. On the contrary, in water environment the wettability presents important contribution to the properties of contact surfaces - hydrophobic surfaces express lower friction coefficient, especially at higher densities of μ-channels. The EDS analysis of worn and unworn surfaces is performed indicating the difference in Si wt% in air and water environment connected to the difference in coefficient of friction.
For the passive mode-locking, a fiber laser with figure-eight structure that incorporates a nonlinear amplifying loop mirror as a saturable absorber is proposed and demonstrated.
Phosphate fiber Bragg grating (FBG) is desired to improve performance of recently developed high power single frequency lasers that were based on highly rare earth ion doped phosphate fibers because these lasers were fabricated with silica FBGs that have incompatible properties with standard phosphate glasses.
This thesis describes to solve the problem of higher power generation of Brillouin fiber lasers (BFLs), to measure their linewidth as a challenging issue and to generate multiwavelength Brillouin fiber laser (MBFL) sources as an application of BFL generation in the both linear and ring cavities. By using the proposed ring cavity with the same components used in the conventional ring cavities, a new Brillouin fiber ring laser (BFRL) with higher output power has been generated. The proposed BFRL configuration shows an output peak power of -0.5 dBm, which is 5.7 dB higher compared to the conventional configuration. In the proposed linear cavity, BFL configuration has been demonstrated by incorporating a 3-dB coupler, a 95/5 coupler, two optical circulators, and a 25 km SMF that allows very high conversation efficiency from the Brillouin pump (BP) to the BFL compared with the conventional linear cavity BFL. Stable BFL operation was obtained at an up-shifted wavelength of 0.086 nm from the pump wavelength with the BFL peak power at -1 dBm, which is 12.3 dB higher than the conventional BFL with the same BP power 13 dBm, due to the reduced cavity loss in the proposed configuration. In the MBFL generation, more than 14 and 9 BFL lines are demonstrated in the ring and linear cavities, respectively. In the ring cavity, the both wavelength spacing 0.08 nm (~10 GHz) and 0.16 nm (~20 GHz) are obtained with the bi - directional multi-wavelength generation whereas in the linear cavity only the wavelength spacing 0.08 nm (~10 GHz) is obtained. The used BP powers are about 14 dBm and 11.7 dBm in respectively the ring and linear MBFL generation. By using a Bismuth Erbium doped fiber amplifier (Bi-EDFA) in the linear BFL cavity, multiwavelength Brillouin Erbium fiber laser (MBEFL) has been ii demonstrated in the L band wavelength region (1565-1625 nm). The generated MBEFL has more number of lines (~50 lines) in comparision with the MBFL by using the Bi-EDFA pumped bidirectionaly with two EDFA pump power 125 mW and Brillouin pump power 5 dBm. The MBEFL generation is limited to the Bi- EDFA operational wavelength region (1525-1625 nm) although it is extended to L band region by using Bi-EDFA in comparison with the traditional MBEFL which can be generated only in the C band wavelength region (1525-1565 nm). In addition, multiwavelength Brillouin Raman fiber laser (MBRFL) is also generated by using a Raman amplifier in a BFL cavity with a 25 km single-mode fiber as the nonlinear gain medium. The second and the third Brillouin stoke waves are obtained by using the Raman pump power 150 mW and Brillouin pump 5.5 dBm at the BP wavelength 1568 nm. The anti-Stokes line is also produced due to fourwave mixing phenomenon. The number of MBRFL lines can be increased by using higher Raman pump power in addition to an optical fiber with the higher Raman gain such as dispersion compensating fiber (DCF). As a high coherent light source with ultranarrow linewidth, Brillouin fiber lasers have been used in many applications especially in microwave generation, gyroscopes. BFL linewidth measurement has also been a challenging research due to the ultranarrow BFL linewidth. In this work, the BFL linewidth has been measured 8 Hz and 24 Hz by using BP linewidth 15 MHz and 124 MHz, respectively. This measurement has been done by the heterodyne method between two independent BFLs. The measured BFL linewidth values are in the range a few hertz as expected from the most of the last reports.
Laser parameters such as noise, chirp, and resonance frequency were characterized by propagation in dispersive fiber,and fitting the parameters to a model for the fiber.
Theory and experiment indicated direct laser modulation enhancement by a uniform fiber Bragg grating by 7 dB at modulation frequencies, of up to 25 GHz, and also noise reduction of 2 dB at frequencies up to 15 GHz.
Some of the beneficial characteristics of this fiber laser include long cavity size (80 cm), 80 dB signal-to-noise ratio, high side mode suppression ratio, and white noise linewidth as narrow as 2 kHz.
A comparison was made between our fiber ring laser and a standard high grade distributed feedback semiconductor laser in transmitting 10 Gbits/sec data.
Uni-directional ring cavity has shown to be the most robust method for producing single frequency laser.
The purpose of this study is to develop compact, low-cost and high-efficiency single frequency IR, green and blue lasers.
Starting with a review of the Erbium doped fiber amplifier, this thesis will describe the construction, intensity noise, linewidth, stabilization techniques, and spectroscopic applications of the Erbium doped fiber ring laser developed as a part of the thesis research activity. This laser, which uses the Erbium doped fiber amplifier as its gain module within fiber based ring resonator, exhibits excellent sidemode suppression (>70dB) and intensity noise properties (shot noise limited beyond GHz regime) with ultranarrow linewidth (
To measure and improve these performance, several new techniques were developed. A new interferometer based on a loss-compensated recirculating delayed self heterodyne technique, for the measurement of ultranarrow linewidth. A novel intracavity filtering technique to make the laser operate at the shot noise floor of intensity noise. Extension of Pound-Drever locking technique into the laser cavity, to enable the laser be stabilized and locked to an external reference at the same time.
The laser was also applied as a spectroscopic tool to study the four wave mixing process in semiconductor optical amplifiers. Because of the ultranarrow linewidth and intensity noise characteristics of fiber laser, it was possible to resolve THz intraband dynamics in a quantum well amplifier.
This thesis will also cover mode locked operation of the fiber laser and related issues briefly in the appendix.
This thesis will present experiments and analysis of two high-dimensional systems, coupled fiber ring lasers and a liquid crystal spatial light modulator with optoelectronic feedback.
Finally, a non-planar figure “8”1064-nm ring laser were developed using the multi-reentrant ring cavity, and controlled beam path at uni-directional operation.
This symmetrical two-mirror figure “8” ring cavity has the merit of compact, few optical elements, and easy design.