A high efficiency dye laser tunable from the UV to the IR

A dye laser has been developed as a source of tunable radiation in the wavelength range 3500–3700 Å. A Variety of dyes and dye mixtures have been used to cover this range. Output powers up to 30 kW are obtained with line-widths less than 1.8 Å. A Fabry-Pérot etalon reduces the output linewidth to 0.1 Å and the peak output power by a factor of three. Second harmonic powers in excess of 2 kW have been generated from the output of this laser.     

The generation of tunable near IR radiation using a nitrogen laser pumped dye laser

Excitation transfer between the two components of a dye mixture has allowed a near IR dye laser to be pumped by a nitrogen laser. Several dye mixtures were employed to achieve lasing at all wavelengths within the range 6400–7720 Å. The output pulse powers were in excess of 10 kW over most of this range.     

Automatic wavelength control of a flashlamp-pumped dye laser

This paper describes a technique for automatically tuning a flashlamp-pumped dye laser to the sodium D₂ line with a precision of ±2 pm (0.02 Å). The same technique could be used for tuning to other emission lines for which a monochromatic source of reasonable intensity is available. A slight modification of the method would enable the laser to be accurately tuned within a range ±10 pm (0.1 Å) of the given emission line.     

Phase conjugation in potassium vapour using subnanosecond laser pulses

Phase conjugated waves (PCW) were generated for the first time by degenerate four-wave mixing with subnanosecond laser pulses in potassium vapour near the D ₁ transition at 7699 Å. The light source was a long cavity grazing incidence dye laser. The pulses had a duration of 700–800 ps and a linewidth of 0.2 Å. The experiments were performed in a temperature range of 400–550° C. A maximum reflectivity of 57% has been observed together with temporal pulse shortening. PCW reflectivity has been measured as a function of the temperature, and the backward pump intensity.     

A powerful broad band tunable dye laser

Perchloric acid solutions of 4 methylumbelliferone pumped by a second harmonic of ruby provide a high efficiency (20% conversion yield of pumping source) broad band (5600-4600 Å) tunable dye laser. Some effects of chemical quenching on the efficiency of this protonic exciplex laser were investigated.     

Travelling-wave-pumped ultrashort-pulse distributed-feedback dye laser

A travelling-wave pumping scheme is used to excite a distributed feedback dye laser. Output pulse shortening below the resolution limit of the streak camera system (1.9 ps) is observed when the velocity of the travelling pump wave is properly matched to the velocity of the laser emission. The pulse spectrum has been measured simultaneously. It consists of a single line of 4 Å width.     

Instantaneous gain and excited state absorption in two carbocyanine dyes

The single-pass gain of 4 · 10^–5 mole/liter solutions of 3,3-diethylthiatricarbocyanine iodide (DTTC) in methanol and 3,3-diethylthiadicarbocyanine iodide (DTDC) in acetone, optically pumped by a giant pulse ruby laser, were measured as a function of pump power, wavelength, and time. The transverse pumping laser pulse was synchronized with a probing pulse from a dye laser. Both low-signal and saturated gain measurements were made in the wavelength range 7860–8066 Å for DTTC and 7059–7412 Å for DTDC dye. The pumping pulse widths at half-power were 15 ± 5 nsec, and the pumping power density was varied over a range of 0–7 MW/cm². Using a steady-state theory, lifetime and cross sections for excited states were determined.This research is supported by the National Research Council of Canada. A summary of the present work was reported at the First All-Union Conference on Complex Organic Dye Lasers, Minsk, USSR, October 22–24, 1975.Published in Zhurnal Prikladnoi Spektroskopii, Vol. 26, No. 3, pp. 487–496, March, 1977.     

Densities and velocity distributions of atomic hydrogen and carbon,measured by laser-induced fluorescence with frequency tripling into the vacuum UV

By focussing a commercial dye laser pumped with a XeCl excimer laser into phase matched Xe-A or Kr-A gas mixtures, radiation at the third-harmonic frequency has been generated in the wavelength regions: 1142–1165, 1178–1186, 1203–1224, and 1268–1290 Å. VUV powers up to about 200 W have been detected by a calibrated Au-photodiode. The vacuum uv radiation has been used for the fluorescence excitation of H and C atoms produced by thermal dissociation or by a gas discharge. Absolute densities have been derived by a comparison of fluorescence intensities with intensities from Rayleigh scattering in argon. As a further application, velocity distributions of C atoms sputtered from a graphite target by 1.5 keV argon ions have been measured. These data are in good agreement with a Thompson distribution corresponding to a surface energy of 8.2 eV.     

Pulse properties of a synchronously mode-locked,cavity dumped,picosecond dye laser system

A synchronously mode-locked, cavity-dumped picosecond dye laser is described. The structure and intensity of the picosecond pulses measured under different conditions are reported. It was found that the structure of the pulses from the synchronously pumped dye laser depends critically on the length of the Ar⁺ laser pulses. At the shortest Ar⁺ laser pulses of about 70 ps the dye pulses are as short as 1.1 ps. With Ar⁺ laser pulses of 200 ps the dye laser pulses contains a broad satellite pulse which contains a large fraction of the total intensity. When a cavity dumper is added to the system one gets dye laser pulses 15–20 ps long with a substructure, which indicates incomplete mode-locking. Well mode-locked 1.5–2.0 ps pulses were obtained in the red part of the dye laser action spectrum, i.e. 620–650 nm for R6G, 595–608 nm for R 110 and 657–662 nm for RB, respectively. Addition of mode-locking dyes also improved the pulse quality at some wavelengths.     

On anti-stokes luminescence from Rhodamine 6G in ethanol solutions

Anti-Stokes luminescence form Rhodamine 6G ethanol solutions excited by a He-Ne laser is observed to be strongly temperature dependent. A theoretical model is proposed for the absorption line shape on the long wavelength side of the pure electronic transition which fits the absorption and luminescence data. Vavilov's law is found to hold even when the absorption coefficient is 10^-6 times the peak absorption coefficient for the Rhodamine 6G dye solution. Another luminescence peak at 6650 Å is observed which is attributed to impurity fluorescence. It could not be related to photochemical products.     

Influence of dye gain medium flow on the wavelength jitter and the drift of high repetition rate—Single mode dye lasers

This paper presents the effect of the flow of the dye gain medium on the wavelength jitter (<30 s) and drift (≈10 min) of a single axial mode dye laser pumped by a copper vapor laser (5.5 kHz). The study was carried out using a wave-meter. The dye solution temperature was maintained to within ±0.1 °C to allow the influence of dye flow rate on the wavelength stability. For the investigated dye flow rate, varying from 1.4 to 2.8 lpm (with corresponding Reynolds number varying from 1975 to 3950), the dye laser wavelength jitter reduced from ±0.15 pm (±130 MHz) to ±0.08 pm (±70 MHz) and drift rate reduced from 1.0 to 0. 2 MHz/s. However for flows beyond 1.7 lpm, random fluctuations in dye laser wavelength were observed. The observed behavior was linked to the flow related variation of angular spread and angular drift of the dye laser beam circulating in the cavity. This was revealed by an exhaustive study of the long term (≈10 min) divergence and pointing stability of the single mode dye laser output beams for different dye media flows.     

Application of a newly developed CCD for spectral-width measurements of a 53 eV germanium laser

We report the application of a soft X-ray CCD for X-ray laser experiments. A newly developed CCD which has a thinned protection layer (SiO₂) of about 0.2 m was attached to a grazing incidence spectrometer with a resolving power of 16000 in order to measure high-resolution spectra of a germanium soft X-ray laser. Clear spectra have been recorded with a high sensitivity in the energy range between 51 eV (240 Å) and 55 eV (225 Å). In addition to the two strong lasing lines at 236 Å and 232 Å, more than 20 weak spontaneous emission lines have been recorded in this energy range. The spectral width of the 236 Å lasing line is approximately 20.5 mÅ at the full width at half maximum. It is shown that this direct X-ray detection system has a spatial resolution of about 1/10 of the CCD pixel size in this spectral measurement.     

Laser induced fluorescence line narrowing in iodine

A complementary technique to Lamb dip absorption spectroscopy in gases is described which allows observation of homogeneous linewidths in fluorescence. Hyperline spectra of iodine excited by a single mode argon laser beam at 5145 Å are presented for the 43-13 and 43-11 bands at 5970 and 5830 Å respectively.     

Soft X-ray amplification by Li-like Al10+ and Si11+ ions in recombining plasmas

Experimental studies of soft X-ray lasers were carried out on the six-beam laser facility and the LF 12 laser facility of SIOM. Using a home-made one-dimensional spatially resolved grazing incidence grating spectrograph, XUV amplification has been observed in Li-like aluminum and silicon ions, by irradiation of slab targets with a line-focused laser. Based on time-integrated measurement, gain coefficients are 3.1 cm^–1 for the 105.7 Å 5f–3d transition in Li-like Al ions, and 1.5 cm^–1 and 1.4 cm^–1 for the 88.9 Å 5f–3d and the 87.3 Å 5d–3p transitions in Li-like Si ions, respectively. The maximum gain × length products (GL) are about 2.5.     

Studies of tunable four-photon parametric fluorescence of crystals in the visible region

Tunable four-photon parametric fluorescence, which is valuable for investigating material nonlinearities and parametric devices, was studied theoretically and experimentally.Theoretical analysis leads to the conclusion that the emitted power depends directly on the focusing of the pumping beam, unlike the process of three-photon parametric fluorescence which is independent of the focusing of the pumping beam. The calculation of the phasematching conditions for nonlinear crystals such as KDP, ADP, TiO₂ and CdS shows that collinear phase-matching can be realised over the visible region using a ruby laser for pumping. Experimentally, tunable emission was observed in the visible range from 4200 Å to 5300 Å with KDP and ADP crystals pumped by a Q-switched ruby laser.     

Sorption study of an anionic dye - benzopurpurine 4B - on calcined and uncalcined Mg-Al layered double hydroxides

In this paper, the elimination from aqueous solution of the pollutant benzopurpurine 4B by Mg-Al-CO₃ hydrotalcite and its modified form Mg-Al-500 has been studied. Mg-Al-CO₃²⁻ layered double hydroxide with an Mg/Al molar ratio of 2.0 was synthesized by the co-precipitation method, and its modification was carried out by calcination. The affinity of these materials with a mixture of benzopurpurine 4B was studied as a function of dye-adsorbent contact time, initial pH of the solution, initial dye concentration and temperature. The results indicate that HDLs were effective in removing benzopurpurine 4B anionic dye. Their saturated adsorption capacities are very high, particularly for the calcined material Mg-Al-500 compared to the standard one Mg-Al-CO₃²⁻.The characterisation of the solid Mg-Al-500, both fresh and after removal of the dye by X-ray diffraction and infrared spectroscopy, shows that the benzopurpurine 4B adsorption on this calcined phase is enhanced by reconstruction of a matrix hydrotalcite intercalated by the dye, with basal spacing of 23.77 Å, which is larger than that of Mg-Al-CO₃²⁻ LDHs (7.57 Å).     

Laser action in a gallium hollow cathode discharge

cw laser action was observed for the 6335 and 7199 Å transitions of Ga II in a hollow cathode discharge. Charge exchange and radiative cascade processes are suggested to be responsible for the population of the upper laser levels.     

A study on the control of dye solution temperature on the line-width and wavelength stability of a copper vapour laser pumped single mode dye laser

This paper presents a study on the line-width and wavelength stability of a single mode narrow line-width (≈ 100 MHz) dye laser pumped by a copper vapour laser, with and without precision temperature control of dye solution. The single mode dye laser system was based on a specially designed SS metal dye cell and grazing incidence grating (GIG) dye resonator with intra-cavity double prism beam expander and etalon. A high precision wavelength-meter was used to record the line-width and frequency stability data. With the coarse dye solution temperature control of 23 ± 2 °C, dye laser line-width varied in a periodic fashion (in every 30 s) between 100 and 770 MHz. Frequency stability was ± 215 MHz (1 min). This is attributed to switching from single to double mode due to temperature induced cavity length change. For the precise dye solution control of 23 ± 0.1 °C, the periodic variation of the line-width was removed completely and the line-width was always ≤ 100 MHz. The frequency stability also improved to ± 42 MHz (1 min). It is established that the dye temperature control is very crucial for achieving, highly frequency stable single axial mode operation.     

Efficient lasing action from Rhodamine-110 (Rh-110) impregnated sol-gel silica samples prepared by dip method

Rhodamine-110/sol-gel samples are prepared by sol-gel technique using dip method. Concentration dependent photophysical studies of these samples have indicated about the least possibility of aggregate formation. The lasing action of Rh-110 in silica samples is studied as a function of dye concentration. An efficient laser emission is observed when the samples are transversely pumped at 337.1 nm and 1.5 Hz repetition rate using a nitrogen laser (400 μJ energy/pulse and 4 ns pulse duration). The maximum of 166% laser efficiency of dye doped sol-gel samples compared to Rhodamine-6G (Rh-6G) in methanol is achieved. The photostability is also measured by using N₂ laser at 1 Hz and it is found nearly 165 pulses. The possible reasons for the photodegradation of the dye molecules are discussed in detail.     

Tunable distributed-feedback laser based on dye doped microporous quartz glass

The first distributed feedback (DFB) dye laser on the basis of microporous quartz glass (MQG) is reported. MQG consists of a specially processed quartz sample doped with a dye. As a pumping source a second harmonic YAG: Nd³⁺ laser with 12.5 pps repetition rate was used. Stable generation of the narrow line tuned within a spectral range of 562–584 nm and 633–663 nm with a linewidth of 0.04 nm was obtained. A high photochemical stability of the dye in the quartz matrix and reliability of MQG as an active medium for the tunable DFB laser were experimentally demonstrated.