Rhodamine 6G Dye Laser Research Articles

Laser lithotripsy of difficult bile duct stones — Results in 50 patients using a rhodamine-6G dye laser with optical stone-tissue detection system

Laser lithotripsy of difficult bile duct stones — Results in 50 patients using a rhodamine-6G dye laser with optical stone-tissue detection system

Effect of Excitation Wavelengths in Pulsed Dye Lasers.

In order to develop a high-efficiency pulsed dye laser, laser efficiencies of various dyes were measured at three different pumping wavelengths of the Cu vapor laser (511 nm and 578 nm) and the frequency-doubled Nd:YAG laser (532 nm) in the same condition. A simulation model for Rhodamine 6G (R-6G) dye laser was also developed to analyze the effect of excitation wavelengths. Some Rhodamine dyes show higher efficiency than those of R-6G in simultaneous two-wavelength pumping by a Cu vapor laser. A dye mixture of Cresyl Violet 670 and Rhodamine 640 was as efficient as R-6G in the 653-660nm region.

Photoacoustic analysis of stimulated emission in pulsed dye lasers

Stimulated emission in pulsed dye lasers was characterized in several experimental conditions by analyzing the changes in the acoustic signals generated in a dye solution, with the dye laser cavity either active or inhibited (i.e., by blocking the optical path or misaligning of the optical components). Pump energy threshold, optimum dye concentration, tuning range and maximum-emission wavelength of a rhodamine 6G dye laser were measured by this method. An approximate model for the photoacoustic signal generation consistent with the experiments is presented.

Experimental and theoretical investigation of a multipass, plane mirror, femtosecond dye laser amplifier

Femtosecond pulses of a passive mode-locked Rhodamine-6G dye laser are amplified in a double-stage, three-pass, plane mirror, Sulforhodamine-101 amplifier system. Saturable filters (Schott glass RG645 and Malachite Green) are used to suppress amplified spontaneous emission. Input pulses of 110-fs duration are broadened to 240 fs in the amplifier system and recompressed to 75 fs in a prism-pair compressor. Using a 20-Hz Q-switched Nd:YAG pump laser of 50-mJ second-harmonic output energy, we obtained amplified and recompressed pulses of 180-µJ energy at 625 nm starting with 40-pJ input pulses. The small-signal amplification dynamics is studied numerically. Relevant gain dye and saturable filter parameters are derived. The influence of amplified spontaneous emission is analyzed.

Line narrowing in the dye solution with scattering centers

As was shown by Markushev et al. [1], laser-like emission without cavity can be obtained from a scattering gain medium, such as powder of Nd doped laser crystals. In the recent work by Lawandy et al. [2] a close phenomenon was observed in a concentrated rhodamine 640 dye solution in the presence of scatterers. The work in Ref. [2] is the first where gain and scattering are separate. In this case lasing evidently is not initiated within the particles, in contrast to the Markushev et al. case, where the gain is in the particles, which supports morphology-dependent resonances. The work by Sha et al. [3] showed similar results in concentrated dye, but it also showed that introduction of a low density of scatterers raises the threshold required for the laser-like effects in the low-concentrated dye. We carried out our own experiments in rhodamine 6G laser dye and observed the laser-like effects both in dilute and concentrated dye with and without scatterers. In our experiment the wavelength of stimulated emission was strongly dependent on the scatterers' concentration. Our observations and some results of Refs. [2,3] are explained with a simple ASE (amplified spontaneous emission) model.

Operation of Rhodamine 6G Dye Laser in Water Solution

The ethanolic solution of Rhodamine 6G is used for dye lasers in the atomic vapor laser isotope separation (AVLIS) system. However, the water solution is preferable from the standpoint of easy treatment and safety. In this paper, we systematically investigated the laser efficiency of a Rhodamine 6G dye laser pumped by a frequency-doubled Nd:YAG laser, for various water-based solutions with surface-active agents and alcohols. By adding an appropriate amount of surface-active agent (Triton X or Emulgen) or alcohol (ethanol or propanol), we obtained almost the same level of laser efficiency as in the pure ethanolic solution. The improvement in the laser efficiency with these additives was attained by the deaggregation of nonradiative dimers. It was also confirmed that the water-based solution showed better performance against thermal distortion than the ethanolic solution, and was suitable for copper vapor laser (CVL) pumping.

Regenerative-feedback mode-locked dye laser: influence of the acousto-optic mode locker

A regenerative-feedback AM-mode-locked Rhodamine 6G dye laser is described. The laser delivers pulses of 0.8-ps duration with 40-mW average output power. The influence of the acousto-optic modulator on the output spectra, which came to be important for broad-bandwidth lasers, is also discussed.

Tuning Range Improvement of a Rhodamine 6G Dye Laser by Addition of KOH to the Solution.

Tuning Range Improvement of a Rhodamine 6G Dye Laser by Addition of KOH to the Solution.

Fluorescence intensity and anisotropy decays of the DNA stain Hoechst 33342 resulting from one-photon and two-photon excitation

We examined the steady-state and time-resolved fluorescence spectral properties of the DNA stain Hoechst 33342 for one-photon (OPE) and two-photon (TPE) excitation. Hoechst 33342 was found to display a large cross section for two-photon excitation within the fundamental wavelength range of pyridine 2 and rhodamine 6G dye lasers, 690 to 770 and 560 to 630 nm, respectively. The time-resolved measurements show that intensity decays are similar for OPE- and TPE. The anisotropy decay measurements of Hoechst 33342 in ethanol revealed the same correlation times for TPE as observed for OPE. However, the zero-time anisotropies recovered from anisotropy decay measurements are 1.4-fold higher for TPE than for OPE. The anisotropy spectra of Hoechst 33342 were examined in glycerol at -20°C, revealing limiting values close to the theoretical limits for OPE (0.4) and TPE (0.57). The steady-state anisotropy for OPE decreases in the shorter-wavelength region (R6G dye laser, 280-315 nm), but the two-photon anisotropy for 560 to 630-nm excitation remains as high as in the long-wavelength region (690-770 nm). This result suggests that one-photon absorption is due to two electronic, but only one transition contributes to the two-photon absorption over the wavelength range from 580 to 770 nm. Our demonstration of these favorable two-photon properties for Hoechst 33342, and the high photostability of the dye reported by other laboratories, suggests that this dye will be valuable for time-resolved studies of DNA with TPE and for two-photon fluorescence microscopy.

Photoacoustic observation of excited singlet state absorption in the laser dye rhodamine 6G

S1 to S3 excited singlet state absorption and two-photon absorption in Rhodamine 6G at the pump wavelengths of 532 and 1064 nm respectively are investigated. The advantages of employing the pulsed photoacoustic technique for conveniently observing excited singlet state absorption are discussed. It is shown that, since photoacoustics and fluorescence are complementary phenomena, analysis using both techniques will yield a better understanding of optical processes in molecules like Rhodamine 6G.

The quantitative determination of the S0—T1 absorption in pyrene with the use of intracavity absorption spectroscopy

Abstract The spin-forbidden S 0 — T 1 transition of pyrene was quantitatively investigated by applying intracavity absorption spectroscopy. The measurements were carried out in benzolic solutions. The molar decadic extinction coefficient of the 0—0 transition was determined to 6.0 × 10 −4 dm 3 mol −1 cm −1 . The integral absorptivity was calculated to 2.94 × 10 −2 dm 3 mol −1 cm −1 and yielded an intrinsic phosphorescence lifetime of 55.4 s. The intracavity absorptions were measured in a cavity-dumped Rhodamine 6G dye laser. Absorbances were recorded in the range between 8 × 10 −4 and 5 × 10 −6 .

Recent advance to 3 × 10^−5 rad near diffraction-limited beam divergence of dye laser with transverse-discharge flash-lamp pumping

A new experimental setup of a Rhodamine 6G dye laser with a transverse-discharge flash-lamp-pumping system is presented. It differs from a previous setup [Sov. J. Quantum Electron. 16, 468-471 (1989)] in that it has a larger laser beam aperture (32 mm) and higher pumping energy (1 kJ), which made it possible to test the scalability and reach near diffraction-limited laser beam divergence of 3 × 10(-5) rad FWHM at beam energy 1.4 J. The effect of spectral dispersion in the active medium and of other optical elements on the beam divergence is also discussed.

Short-cavity dye lasers with frozen ethanol solvents

Short-cavity (10–500 μm) rhodamine 6G dye lasers were operated with pumping of a N2 laser (100 kW) when a solution of dye in ethanol was frozen with liquid nitrogen (77 K) into ice. Laser wavelengths shifted to shorter ones. Axial modes of the laser output were determined, as other lasers, with the optical cavity lengths. Relaxation oscillations and short pulses less than 1 ns were also obtained.

Pump and signal cross saturation in cw dye lasers

It is well known that the signal output intensity from a dye laser oscillator depends directly on the pump intensity. The opposite effect, the dependence of the transmitted pump intensity on the signal intensity, is studied in detail. The theoretical results are compared with experimental data obtained using an argon-laser-pumped rhodamine 6G dye laser.

Laser lithotripsy of difficult bile duct stones by means of a rhodamine-6G laser and an integrated automatic stone-tissue detection system

This report describes the initial clinical implementation of a new laser lithotripter system capable of effective fragmentation of common bile duct stones with a high degree of safety provided by an integrated stone-tissue detection system. This system automatically terminates laser pulse transmission if tissue contact is sensed. Eighteen patients with giant or impacted common bile duct stones refractory to standard treatment techniques were treated via the endoscopic retrograde route using a rhodamine-6G dye laser with an integrated stone-tissue detection system. In the event of tissue contact, the stone-tissue detection system cuts off the laser pulse after 190 ns (after transmission of 5% to 8% of the total pulse energy). Nine patients were treated under cholangioscopic control, and nine patients were treated blindly under fluoroscopic control using only standard duodenoscopes with either a 6F standard endoscopic retrograde cholangiopancreatography catheter (4 patients), a 6.8F balloon catheter (3 patients), or a laser lithotriptor basket (2 patients). Laser-induced fragmentation was achieved in all 18 patients (100%). Sixteen of 18 patients (89%) became completely stone-free after completion of the treatment, including additional intracorporeal shock wave lithotripsy in five patients. The only major complications occurred in one fully anticoagulated patient with a prosthetic heart valve who developed significant hemobilia and transient cholangitis but recovered after conservative treatment. Laser lithotripsy using the rhodamine-6G dye laser plus stone-tissue detection system appears safe and effective and allows "blind" fragmentation of difficult common bile duct stones to be performed under radiologic control.

Growth and low-threshold laser oscillation of an epitaxially grown Nd:YAG waveguide

We report 1.064-microm laser operation of an epitaxially grown Nd: YAG planar waveguide with thresholds as low as ~0.7 mW when high-reflectivity mirrors are used. The output is single mode and, when a 83% reflectivity output coupler is used, has a diode pumped slope efficiency of ~40%. Output powers in excess of 60 mW have been obtained when pumping with a Rhodamine 6G dye laser.

Generation of frequency tunable femtosecond pulses in a cw pumped linear dispersion-balanced passive mode-locked rhodamine 6G dye laser

Frequency tunable femtosecond light pulses are generated in a cw pumped linear group velocity dispersion balanced passive mode-locked rhodamine 6G dye laser by birefringent filter tuning. The saturable absorbers DODCI (duration Δ t L < 100 fs in frequency region between 607 nm and 620 nm), DQOCI (Δ t L < 100 fs between 585 nm and 615 nm), and TCVEBI (Δ t L < 100 fs between 585 nm and 615 nm) in ethylene glycol were applied.

Continuous-wave infrared laser spectrometer based on difference frequency generation in AgGaS_2 for high-resolution spectroscopy

A high-resolution cw spectrometer based on difference frequency generation (DFG) in a 20-mm-long AgGaS2 crystal pumped by two stabilized single-frequency cw dye–Ti:sapphire lasers is described. Experiments performed with a Rhodamine 6G and DCM dye laser combination pumped by a 20-W argon laser are reported. Informed radiation is generated from 7 to 9 μm with an ultranarrow linewidth (<0.5 MHz) and an output power 1 μW by making use of 90° type I phase matching. The performance of the DFG laser spectrometer is evaluated by using a portion of the ν2 band of NH3 near 1177 cm−1.

Photochemical behaviour of rhodamine 6G in Nafion membrane

Sorption of laser dye rhodamine 6G in perfluorosulphonate cation-exchange membrane (Nafion) from aqueous solution has been investigated by optical absorption and emission studies. In the H+ form, the optical absorption spectra changes with water content in the membrane and is attributed to the change in H+ ion concentration in dry and wet (with water) conditions of the membrane. The dye is present in the protonated form in the dry membrane and in the cationic form in the wet membrane. In the Na+ form, rhodamine 6G is present in the cationic form and the optical absorption spectra do not show changes in dry and water-wet conditions of the membrane. The fluorescence lifetime of rhodamine 6G is 3.97 ns and decay is single exponential. In the Na+ and H+ forms of the membrane, the fluorescence decay is biexponential. The lifetime and the relative ratio vary for the Na+ and H+ forms and also with the water content in the membrane. Owing to the large size of the dye low values for the diffusion coefficient are observed (3.2 × 10–11 and 2.0 × 10–8 cm2 s–1 for Na+ and H+ form of Nafion, respectively). As compared to aqueous solutions, rhodamine 6G in Nafion membrane is observed to be photostable.

Pump polarization effects in cw dye lasers

The effects of pump polarization on the performance of cw dye lasers have been investigated. A recently developed semiclassical model for synchronously pumped mode-locked dye lasers is adapted to the problem of cw dye-laser oscillation, and analytic expressions are obtained for the relationship between the pump power, pump polarization, and dye-laser output power. The theoretical results are compared with experimental data obtained using an argon-laser-pumped rhodamine 6G dye laser.