Copper vapour laser (CVL) pumped dye lasers offer a source of high power, kilohertz repetition rate, tunable narrow-bandwidth radiation suitable for many spectroscopic applications in the visible and infra-red. Furthermore, the nonlinear frequency conversion of CVL-pumped dye laser radiation extends the wavelength range of these laser sources into the blue and ultra-violet. A series of experimental investigations have been undertaken to gain a physical understanding of the fundamental parameters necessary for the optimization of the CVL-pumping of dye lasers. Issues addressed include the influence of the CVL cavity design, the pump beam polarization and geometry, the dye oscillator cavity design, the choice of grating materials, and the dye flow rate. A model based on the rate equation analysis of the kinetic processes relevant to optical amplification in dye lasers has been developed, and the results have been used to design amplifiers with extraction efficiencies in excess of 45 %. As a result of the aforementioned investigations, three commercially available pulsed dye lasers have been successfully optimized for CVL-pumping for the first time. Once modified, these dye lasers have typically shown conversion efficiencies in excess of 20%, with frequency bandwidths as narrow as 800MHz, and beam qualities approaching the diffraction limit. The theory of second harmonic generation is reviewed, and a suite of corresponding computer models have been developed to form the basis for a coherent experimental investigation of UV generation using the CVL and CVL-pumped dye lasers. CVL SHG has been demonstrated in jS-barium borate (BBO) and lithium triborate (LBO), with SHG efficiencies in excess of 18% realized for the CVL 511nm line in BBO. For the first time, an experimental comparison of spherically and elliptically focused second harmonic generation has been undertaken. Optimized elliptical focusing is found to be up to 30% more efficient than using conventional spherical focusing in agreement with theoretical predictions. The superior divergence and transverse coherence of CVL-pumped dye lasers, in comparison to those of the CVL, is reflected in the SHG efficiencies achieved in BBO, LBO and lithium iodate. Conversion efficiencies approaching 40% have been demonstrated in lithium iodate, with harmonic conversion coefficients approaching 2400mW/W2 realized at low input powers. The Boyd and Kleinman theory of SHG with focused Gaussian beams is found to provide an excellent description of SHG with CVL-pumped dye laser radiation, and accurately predicts the optimum strength of focusing and harmonic conversion coefficient. For the first time, sum frequency mixing (SFM) of the CVL with a dye laser has been demonstrated, and found to provide a potentially efficient source for tunable UV radiation. Finally, the application of CVL-pumped dye lasers to resonant ionization mass spectrometry and tropospheric hydroxyl (OH) radical detection is discussed, and the spectroscopic potential of a frequency doubled CVL-pumped dye is demonstrated by recording the absorption spectrum of OH at 308nm.

Previous studies of distributed feedback dye lasers (DFDL's) have identified that the linewidth of the device scales, to a first approximation, with the level of pumping employed. A more recent development is that the DFDL can be used to produce single ultrashort pulses. To produce such pulses the main requirement is that the laser is operated close to its threshold. An apparent contradiction exists here since, by lowering the pump power to achieve narrow linewidth operation, the near threshold region must be avoided since pulsing operation acts to increase the linewidth (to at least the Fourier transform of the pulse duration). This thesis further investigates the mechanisms which contribute to the temporal and linewidth properties of the laser. It is identified that by judicious choice of operating conditions a regime exists where the DFDL may be operated with a linewidth approaching that of the transform limit for the nanosecond pulse durations involved. After introducing the different types of distributed feedback lasers the thesis first reviews previously understood DFDL behaviour. Different DFDL geometries are considered with a view to their particular temporal and linewidth properties. A strategy for the development of a narrow linewidth DFDL is presented. The experimental laser system is described detailing the operation and characteristics of the frequency doubled Q switched Nd:YAG pump laser and the two different DFDL geometries. A high resolution computer aided interferometry (CAIN) system is described which provided single shot linewidth measurements. This system was used extensively in the experiments reported. DFDL linewidth is seen to depend on the thermo-optical properties of the dye's host solvent and as such a full characterization of commonly used solvents is presented. The temporal behaviour of the laser is considered theoretically with the aid of a coupled rate equation model which describes the interplay between the population inversion and the cavity photon flux. The model is used to predict short (picosecond) and smooth (nanosecond) pulse operation of the laser. Finally, a description of and the results obtained from various experimental investigations into the DFDL are presented. Temporal analysis, using a streak camera, revealed that, as expected, under certain circumstances multiple pulsing of picosecond duration could occur. Different conditions however, lead to narrow linewidth (~100 MHz) operation. A description of the two operating regimes is presented and these are related to the particular parameters involved e.g. the grating length or the level of pumping employed.

This thesis describes the design and development of a frequency doubled, continuous wave dye laser and its application to a study of the high Rydberg states of Rubidium. The laser uses the dye rhodamine 6G as the active medium and is optically pumped with an argon ion laser. Frequency doubling is by an ADA (ammonium dihydrogen arsenate) or ADP (ammonium dihydrogen phosphate) crystal located within the laser cavity. Continuous output powers in the ultra-violet in excess of 30 mW and tunable over the wavelength range 285-315 nm have been produced. The linewidth can be chosen to be 0.02 nm broadband system) or 0.002 nm (narrowband system) depending on the frequency selecting elements used. In order to keep insertion losses small the crystals have optical faces cut at Brewster's angle, and in order to increase generation efficiency the intracavity radiation field is focused into the crystal. Such an arrangement introduces the aberrations of coma and astigmatism which must be compensated by suitable cavity design. A variety of cavity and crystal configurations have been analysed for aberrations, and a novel arrangement for the simultaneous elimination of coma and astigmatism developed. Several practical frequency doubled dye lasers have been investigated. In particular the performances of ADA and ADP as the frequency doubling crystals are compared and contrasted. ADA has the advantage that it can be non-critically phase matched at these wavelengths and this results in a higher generation efficiency and a better UV beam quality than encountered with ADP. However, since it can only be temperature tuned, the tuning range (292-302 nm for temperature range 20-80°C) is more limited than that for ADP (285-315 nm) which can also be angled tuned. For both types of crystal, thermal phase mismatching is identified as the process limiting generation efficiency. Evidence is also presented that thermal focusing ultimately limits the UV output power by upsetting cavity stability. A computer model of intracavity frequency doubling has been developed. Thermal phase mismatching effects in the crystal as well as excited state absorption in the dye are included. This model is used to investigate the influence of cavity losses and crystal absorption on generation efficiency. Optimization of conversion efficiency by correct choice of crystal parameters is considered. Two systems have been developed to allow continuous scanning over an extended frequency range. One allows the broadband laser (0.02 nm) to be continuously tuned over 3 nm, the other allows the narrowband laser (0.002 nm) to be continuously tuned over 2 nm. The operation of a single frequency version of the laser and its stabilization on an external reference cavity is also described. The excitation of high Rydberg states in Rubidium using the frequency doubled laser is described. The states are detected by a space-charge limited ionization detector. The principal series of Rb up to a principal quantum number of n = 74 has been detected. A novel triode arrangement of electrodes in the space charge detector has enabled a small electric field to be applied to the rubidium vapour. The consequent Stark mixing of n2S, n2P and n2S states has allowed the n2S and n2D states to be excited from the 52S ground state. New term values of the n2S and n2D series are reported.

The dynamics of ultrashort pulse generation and amplification in dye lasers is studied in this dissertation. In particular, we have developed general semiclassical models for ultrashort pulse dye laser amplifiers and oscillators. These models start from Maxwell’s equation for the electric field and density matrix equations for the active laser medium. A finite coherence time or phase memory time of the molecular wave functions, a finite vibrational relaxation time for the lower electronic state of the dye laser transition, an isotropic molecular orientational distribution, and an arbitrary pump polarization are all taken into account. Based on these models, specific topics that are discussed herein include pump polarization effects, timing and detuning studies in synchronously pumped mode-locked dye lasers, and amplification of ultrashort pulses in dye laser amplifiers. Properties such as pulse width, pulse shape, pulse intensity, pulse stability, pulse amplification efficiency, etc., are studied in detail.

No description available.

No description available.

by Lam King Shun. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (p. 103-107). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese. / by Lam King Shun.

This thesis describes the development of an intracavity frequency doubled dye laser from a commercial Spectra-Physics 380D single frequency ring dye laser, and the application of this system to a number of spectroscopic studies in discharges. Evaluation of the stability of the laser cavity is carried out, by computer calculation, in order to optimise the optical component set used in the frequency doubled dye laser. Using an ADA (ammonium dihydrogen arsenate) crystal, 17 mW of continuous wave ultra-violet, tunable over the range 292-302 nm, has been produced. The linewidth, when the laser is stabilised, is about 500 kHz in the UV. The CW UV output has been used to measure helium triplet (23S) metastable densities in a positive column discharge as a function of pressure (1-8 Torr) and current (2.5-80 mA). A maximum density of 10x10¹² cm-3 is measured for a pressure of 2 Torr and current of 60mA. The measured metastable densities are used in a rate equation analysis to extract values of the rate coefficient for distraction (by collisions with electrons) of the 23S metastables (1.6x10^-8 cm3s-1 for p = 2 Torr). A study of the optogalvanic signal generated when irradiating a neon positive column discharge with laser light of wavelength 588.2 nm, corresponding to the ls5-2p2 transition, is carried out. The signal is found to change sign as the dye laser power is increased, for some discharge conditions. Spatial studies of the optogalvanic signal in conjunction with absorption and emission studies are carried out to investigate the evolution of the population densities of levels connected to the 1s5 and 2p2 levels. A rate equation model is developed which demonstrates the importance of the 1s3 population density in explaining the observed sign reversal. A high resolution study of two transitions in the UV, in the tungsten spectrum, is presented. The even isotope splittings and the hyperfine splitting between the two strongest hyperfine components on transitions at 294.4 nm and 294.7 nm have been resolved by saturated absorption spectroscopy. From centre of gravity considerations the hyperfine splittings of the three levels involved in the two transitions have been predicted as 1630 MHz for the7s3 level, -506 MHz for the 3692 level and 225 MHz for the 3683 level. A simple wavemeter using a corner-cube Michelson interferometer is described. Digital counting circuits to provide a direct reading of either the fundamental or second harmonic wavelength have been designed and constructed. Wavelength readings accurate to 1 part in 106 are achieved.

In this study an improved description of the bandwidth limiting tuning filters has been introduced into a semiclassical model for a synchronously pumped mode-locked dye laser system. This model is an improvement over the traditional rate equation approach since it has detailed representations of the energy levels, rotational distribution, and coherence effects. The new set of equations has been solved numerically using the best available values for the various parameters, and autocorrelations have been computed for a range of different length detuning and bandwidth limiting elements. In the experiments, an acousto-optically mode-locked argon ion laser is used to synchronously pump a rhodamine 6G dye laser. To study the tuning effects, two and three plate birefringent filters and a tuning wedge have been used. Transmission and bandwidth of these filters have been carefully measured as a function of the length detuning. The autocorrelated pulses have been measured as a function of the length detuning. The experimental pulse shapes agree closely with the theoretical solutions for all values of detuning and filter bandwidth. Through a sensitivity analysis, it is shown how this model can be used to select values for the transmission and the bandwidth of the filter to obtain optimum pulse characteristics.

This dissertation presents experimental and theoretical studies of transient degenerate four wave mixing (DFWM) in organic dyes. Chapter 1 is an introduction to DFWM. Chapter 2 describes DFWM experiments that were performed in the gain medium of a dye laser. Chapter 3 presents the theory of DFWM of short pulses in three level saturable media. Chapter 4 presents DFWM experiments of femtosecond pulses in the saturable absorber of a passively modelocked ring dye laser. Chapter 5 presents the theory of DFWM of ultrashort pulses in resonant media.