Copper vapour laser (CVL) pumped high repetition rate narrow bandwidth dye laser is an important source of tunable radiation. It finds numerous applications in spectroscopic investigations and selective material processing like atomic vapour laser isotope separation (AVLIS). Being wavelength selective in these applications stability of the output wavelength and bandwidth are extremely important. The stability of these parameters depend upon the refractive index fluctuation of the dye medium, due to pump beam induced temperature gradients, dye solution flow, and mechanical stability of optical components. Precise measurement of wavelength and bandwidth of a dye laser and control over parameters governing the variations are important for any stable dye laser system. In this thesis, details of investigations carried out on a Rhodamine 6G dye laser for obtaining stable wavelength and output power are presented. Parameters that affect the stability were identified, monitored and put on close loop control to achieve the desired stability. Pump beam i.e. CVL optical power, dye flow rate and dye solution temperature are mainly these parameters. CVL power is mainly a function of input electrical power and pressure of the buffer gas inside the tube. To monitor and regulate these parameters, different sensors and actuators were selected and interfaced with a master slave topology based data acquisition and control system. The DAQ and control system is designed around a micro controller card based on advanced CPU P80552 and has on chip 8 channel 10 bit multiplexed analog input, 16 TTL digital inputs and 16 digital outputs. It works as slave and PC as master. Following closed loops were designed and incorporated to maintain a stable output: a. Average output of CVL was maintained constant by regulating the electric input power through closed loop control. b. The buffer gas pressure was monitored with a semiconductor pressure sensor and was regulated using pulse width modulation. c. Temperature of the dye solution was monitored with PT100 and was controlled using proportional controller. d. Flow rate of dye solution was controlled using a variable frequency drive (VFD) for the dye circulation pump. e. The dye laser wavelength was monitored by using a high resolution spectrograph and pixel position of the peak from CCD image obtained from spectrograph is used for feedback correction using a pico motor. In the present work with application of the above-mentioned input power and pressure loops, a stable output of CVL, is achieved. Variations in power and pulse width of CVL are got limited to within 2%, from 10% when CVL system was working unregulated. This control system does the line regulations and corrects the input electrical power if variations in discharge current occur due to pressure variation. Every dye cell has limits on flow rate because of its geometry. With flow and temperature control dye cell was characterized to work with lower linewidth. VFD (variable frequency drive) is used for flow regulation. Finally active control on set wavelength was also achieved with resolution of 0.01nm accuracy. Measurement of wavelength was done with 0.3 m, 0.054 nm resolution spectrograph. Closed loop pico motor with 30 nm per step linear resolution was used for wavelength control. The thesis is organized in four chapters. First chapter presents a brief introduction to high repetition rate CVL pumped dye laser, operation of a CVL and parameters affecting the dye laser stability and their control schemes. Literature survey in this chapter is focused on different control mechanisms used with such lasers. Second chapter describes the laser system and interfacing of data acquisition system used for experimental setup. Closed loop controls for different parameters are described in this chapter. It also describes the software algorithms developed for this work. Third chapter presents experimental results and analysis with discussion on performance of the control loops. Finally the conclusion is given and few suggestions are made for further work.

Šioje disertacijoje tiriami nuolatinai kaupinami regeneraciniai stiprintuvai su ilgos relaksacijos trukmės lazerine terpe. Tikslas buvo išanalizuoti bendrus tokių sistemų sudėtingos dinamikos dėsningumus pasireiškiančios aukštų dažnių diapazone ir surasti būdą pasiekti maksimalias išėjimo impulsų energijas išlaikant jų stabilumą. Analitiškai aprašomos pagrindinės optimizuotų ir stabiliame režime veikiančių stiprintuvų charakteristikos, tokios kaip optimalūs pradinis ir galutinis stiprinimo koeficientai, maksimali išėjimo impulso energija, rezonatoriuje išsklaidytoji galia, daugelio praėjimų B-integralas ir rezonatoriaus apėjimų skaičius, su kuriuo gaunama maksimali išėjimo impulso energija. Nustatytos egzistuojančių dinaminių režimų (stabilaus, kvaziperiodinio ir chaotinio) sritys valdančiųjų parametrų erdvėje. Išsiaiškinta, kad nestabilaus veikimo sritis mažėja, kai užkrato impulso energija didėja. Sukurtas ir išplėtotas stabilumo diagramų metodas, kuris ne tik suformuoja sisteminį požiūrį į regeneracinio stiprinimo dinamikos optimizavimą, bet ir leidžia nustatyti užkrato energijos dydį, pakankamą stabiliam veikimui palaikyti. Nustatytos darbinės charakteristikos kritiniame impulsų pasikartojimo dažnių diapazone, kur neegzistuoja analitiniai sprendiniai ir nestabilumai yra labiausiai tikėtini. Teoriniai rezultatai patvirtinti eksperimentiškai diodais kaupinamoje pikosekundinėje Nd:YVO4 lazerinėje sistemoje. Pademonstruota, kad užkrato impulso energijos padidinimas susiaurina... [toliau žr. visą tekstą] / This thesis presents a detailed study of continuously pumped regenerative amplifiers based on long-relaxation-time laser media. The goal of the research was to develop a general pattern of complex dynamics peculiar to such systems at high repetition rates and to find a way to improve performance characteristics affected by instabilities. Basic parameters of the optimally coupled regenerative amplifier operating in stable regime were derived in analytical form. They include optimum initial and final gains, the maximum output pulse energy, the power dissipation, the multi-pass B-integral and the roundtrip number providing the maximum output energy. A comprehensive pattern of existing dynamic regimes (stable, quasi-periodic and chaotic) was represented in space of controlling parameters. It has been found that the space of unstable operation decreases as the seed pulse energy increases. A method of stability diagrams, which forms a systematic approach to the optimization of regenerative amplification dynamics and in particular allows one to determine the seed pulse level sufficient to maintain the operation stable, has been developed. Performance characteristics were determined in the critical range of repetition rates, where instabilities are pronounced at the most and analytical solutions are unavailable. The experiments, carried out using the diode pumped picosecond Nd:YVO4 laser system, exhibited a good agreement with theoretical inferences. It has been demonstrated that... [to full text]

This thesis presents a detailed study of continuously pumped regenerative amplifiers based on long-relaxation-time laser media. The goal of the research was to develop a general pattern of complex dynamics peculiar to such systems at high repetition rates and to find a way to improve performance characteristics affected by instabilities. Basic parameters of the optimally coupled regenerative amplifier operating in stable regime were derived in analytical form. They include optimum initial and final gains, the maximum output pulse energy, the power dissipation, the multi-pass B-integral and the roundtrip number providing the maximum output energy. A comprehensive pattern of existing dynamic regimes (stable, quasi-periodic and chaotic) was represented in space of controlling parameters. It has been found that the space of unstable operation decreases as the seed pulse energy increases. A method of stability diagrams, which forms a systematic approach to the optimization of regenerative amplification dynamics and in particular allows one to determine the seed pulse level sufficient to maintain the operation stable, has been developed. Performance characteristics were determined in the critical range of repetition rates, where instabilities are pronounced at the most and analytical solutions are unavailable. The experiments, carried out using the diode pumped picosecond Nd:YVO4 laser system, exhibited a good agreement with theoretical inferences. It has been demonstrated that... [to full text] / Šioje disertacijoje tiriami nuolatinai kaupinami regeneraciniai stiprintuvai su ilgos relaksacijos trukmės lazerine terpe. Tikslas buvo išanalizuoti bendrus tokių sistemų sudėtingos dinamikos dėsningumus pasireiškiančios aukštų dažnių diapazone ir surasti būdą pasiekti maksimalias išėjimo impulsų energijas išlaikant jų stabilumą. Analitiškai aprašomos pagrindinės optimizuotų ir stabiliame režime veikiančių stiprintuvų charakteristikos, tokios kaip optimalūs pradinis ir galutinis stiprinimo koeficientai, maksimali išėjimo impulso energija, rezonatoriuje išsklaidytoji galia, daugelio praėjimų B-integralas ir rezonatoriaus apėjimų skaičius, su kuriuo gaunama maksimali išėjimo impulso energija. Nustatytos egzistuojančių dinaminių režimų (stabilaus, kvaziperiodinio ir chaotinio) sritys valdančiųjų parametrų erdvėje. Išsiaiškinta, kad nestabilaus veikimo sritis mažėja, kai užkrato impulso energija didėja. Sukurtas ir išplėtotas stabilumo diagramų metodas, kuris ne tik suformuoja sisteminį požiūrį į regeneracinio stiprinimo dinamikos optimizavimą, bet ir leidžia nustatyti užkrato energijos dydį, pakankamą stabiliam veikimui palaikyti. Nustatytos darbinės charakteristikos kritiniame impulsų pasikartojimo dažnių diapazone, kur neegzistuoja analitiniai sprendiniai ir nestabilumai yra labiausiai tikėtini. Teoriniai rezultatai patvirtinti eksperimentiškai diodais kaupinamoje pikosekundinėje Nd:YVO4 lazerinėje sistemoje. Pademonstruota, kad užkrato impulso energijos padidinimas susiaurina... [toliau žr. visą tekstą]