Single-mode Dye Laser Research Articles

Hyperfine-resolved high-resolution laser spectroscopy of 14NO2 radical in the 15885 cm−1 energy region

Hyperfine-resolved high-resolution fluorescence excitation spectrum of the A˜2B2 ← X˜2A1 transition of 14NO2 radical in the 15870–15900 cm−1 energy region was observed, by crossing a jet-cooled molecular beam and an output of a single-mode dye laser at the right angles. We obtained the rotational assignments up to N′ = 11 for the Ka = 0 series and those up to N′ = 7 for the Ka = 1 series by analyzing the observed hyperfine structures and employing the combination differences, and determined the molecular constants of the upper vibronic level. Most of the Fermi contact interaction constants of the rotational levels of the upper vibronic level were found to range from 0.002 cm−1 to 0.004 cm−1. The (Ka′ = 0, N′ = 3, J′ = 3.5) level was found to be strongly perturbed, and we recognized some perturbers in the vicinity of the main rotational level. We concluded that the most plausible candidate of the perturbers in this region is the vibronic levels having almost pure A˜2B2 electronic state character.

Tunable single-mode cw energy-transfer dye laser directly optically pumped by a diode laser

Within this work a tunable single-mode continuous wave energy transfer dye laser operation in green-yellow spectral region was achieved under direct optical pumping by an economy-class diode laser at λ = 445 nm. The laser is operated on a binary dye mixture: Coumarin 498 (donor) and Pyrromethene 556 (acceptor); the latter exhibits only negligible absorption at the pump wavelength, and thus its lasing is almost exclusively due to the excitation energy transfer. This binary energy transfer dye mixture was studied for the first time. Basic lasing properties at various acceptor concentrations were examined; donor concentration was fixed at the value optimum for its lasing under the optical pumping conditions applied. For the final acceptor concentration the optimum output coupling was determined for selected wavelengths from the measurements of the output power in variable output coupling scheme. Single-mode operation sufficiently stable for high-resolution spectroscopic applications was also achieved and tested. Further investigations of the energy transfer mechanisms and efficiency in the binary dye mixture applied are in progress and will be reported separately.

Hyperfine interaction constants of 14NO2 in 14 500-16 800 cm-1 energy region.

We observed hyperfine-resolved high-resolution fluorescence excitation spectra of k = 0, N = 1 ← 0 transitions in 82 vibronic bands of the Ã2B2 ← X̃2A1 system of 14NO2 in the 14 500-16 800 cm-1 region by crossing a jet-cooled molecular beam and a single-mode dye laser beam at right angles. We determined hyperfine interaction constants of the lower and upper states for all the observed vibronic bands based on the analysis of the hyperfine structures of k = 0, N = 1 ← 0 transitions. Most of the determined Fermi contact interaction constants were found to be distributed in 0.0013-0.0038 cm-1, which are intermediate in magnitude between those in lower and higher energy region reported by other groups. A sharp decreasing of the Fermi contact interaction constant was found in 16 200-16 600 cm-1, and it may be caused by the interaction with the dark C̃2A2 state. The hyperfine interaction constants are powerful clues to obtain reliable vibronic assignment. We tentatively assigned vibronic bands located at 14 836 cm-1, 15 586 cm-1, and 16 322 cm-1 as the transitions to the intrinsic (0,7,0), (0,8,0), and (0,9,0) vibrational levels of the Ã2B2 state, respectively.

Single Longitudinal Mode Optofluidic Microring Laser Based on a Hollow-Core Microstructured Optical Fiber

A single longitudinal mode microring dye laser based on a simplified hollow-core microstructured optical fiber (SHMOF) is proposed and demonstrated. The dye laser uses a submicron thickness silica microring embedded in the SHMOF as resonator and has the characteristic of a low threshold of 664 nJ/mm2. The factors that influence the single longitudinal mode excitation are discussed and the possible operation principle is analyzed. Meanwhile, the single longitudinal mode emissions at several different wavelengths are realized by using different dyes as gain medium, which indicates that the lasing wavelength of the laser is scalable. Time domain characteristics of the lasing are also measured and they are synchronous with the lateral pumping laser. The attractive possibility of developing microfluidic single longitudinal mode dye laser within the SHMOF presents opportunities for integrated optics applications and biomedical analysis with high sensitivity.

Tunable continuous wave single-mode dye laser directly pumped by a diode laser

In this work, a tunable continuous wave single-mode ring dye laser (a modified version of Coherent model CR 699-21), directly optically pumped by an economy-class diode laser, has been set up. The laser was operated on Coumarin 498, and its generation profile covered part of the green spectral region not easily accessible in single-mode operation. The performance of the laser in both broad-band and single-mode operation regimes was studied. It was proved that optical pumping by diode lasers allows one to obtain single-mode operation of dye lasers that is sufficiently stable for high-resolution spectroscopy applications.

Single longitudinal mode oscillations in the converging-straight-diverging dye cell pumped by a 9 kHz copper vapor laser

To minimize the thermal and flow induced effect on the single mode dye laser at higher pulse repetition rate several dye cell flow geometries have been studied using computational fluid dynamics (CFD) model. The evolution of velocity profiles along the straight section of a converging – straight – diverging dye cell has been studied and the boundary layer thickness at different locations in the straight section of the flow channel has been captured using the CFD model. It has been observed that the boundary layer thickness reduces with increasing flow velocity in the dye cell. The boundary layer thickness is minimum at the throat of the dye cell i.e., from where the straight section commence and the velocity profile is almost flat. This dye cell provides nearly two times lesser pressure drop for higher flow velocities in comparison to the straight rectangular dye cell. These dye cells have been used for generating single mode oscillation in the short cavity grazing incidence grating (GIG) cavity. We had experimentally observed that the wavelength fluctuations around the mean value is nearly 7 times less for the converging-straight-diverging dye cell at a relatively higher flow velocities of nearly 12m/s. For rectangular straight dye cell it is very difficult to obtain a single mode laser at this higher flow velocity.

High-resolution laser spectroscopy and magnetic effect of the B̃(2)E(')←X̃(2)A2(') transition of the (15)N substituted nitrate radical.

Rotationally resolved high-resolution fluorescence excitation spectra of the 0-0 band of the B̃(2)E(')←X̃(2)A2(') transition of the (15)N substituted nitrate radical were observed for the first time, by crossing a jet-cooled molecular beam and a single-mode dye laser beam at right angles. Several thousand rotational lines were detected in the 15 080-15 103 cm(-1) region. We observed the Zeeman splitting of intense lines up to 360 G in order to obtain secure rotational assignment. Two, nine, and seven rotational line pairs with 0.0248 cm(-1) spacing were assigned to the transitions from the X̃(2)A2(') (υ″ = 0, k″ = 0, N″ = 1, J″ = 0.5 and 1.5) to the (2)E3/2(') (J' = 1.5), (2)E1/2(') (J' = 0.5), and (2)E1/2(') (J' = 1.5) levels, respectively, based on the ground state combination differences and the Zeeman splitting patterns. The observed spectrum was complicated due to the vibronic coupling between the bright B̃(2)E(') (υ = 0) state and surrounding dark vibronic states. Some series of rotational lines other than those from the X̃(2)A2(') (J = 0.5 and 1.5) levels were also assigned by the ground state combination differences and the observed Zeeman splitting. The rotational branch structures were identified, and the molecular constants of the B̃(2)E1/2(') (υ = 0) state were estimated by a deperturbed analysis to be T0 = 15 098.20(4) cm(-1), B = 0.4282(7) cm(-1), and DJ = 4 × 10(-4) cm(-1). In the observed region, both the (2)E1/2(') and (2)E3/2(') spin-orbit components were identified, and the spin-orbit interaction constant of the B̃(2)E(') (υ = 0) state was estimated to be -12 cm(-1) as the lower limit.

Temporal dynamics of high repetition rate pulsed single longitudinal mode dye laser

Theoretical and experimental studies of temporal dynamics of grazing incidence grating (GIG) cavity, single-mode dye laser pumped by high repetition rate copper vapour laser (CVL) are presented. Spectral chirp of the dye laser as they evolve in the cavity due to transient phase dynamics of the amplifier gain medium is studied. Effect of grating efficiency, focal spot size, pump power and other cavity parameters on the temporal behaviour of narrow band dye laser such as build-up time, pulse shape and pulse width is studied using the four level dye laser rate equation and photon evolution equation. These results are compared with experimental observations of GIG single-mode dye laser cavity. The effect of pulse stretching of CVL pump pulse on the temporal dynamics of the dye laser is studied.

High resolution molecular spectroscopic system assisted by an optical frequency comb

We developed a high resolution laser spectroscopic system to study detailed structures and dynamics in excited states of molecules. The cooperation of an optical frequency comb and a single-mode dye laser realized high resolution, high accuracy, and wide tuning range simultaneously with short measurement time and easy operation. To demonstrate the ability of our system, we observed hyperfine spectra of B–X rovibronic transitions of molecular iodine distributed in the range of 570–612 nm. The absolute frequencies of hyperfine components were determined with the uncertainty of about 100 kHz, and vibrational dependences of the hyperfine constants were examined.

Spectroscopic study of the 22Σ+ and the 42Σ+ excited states of LiCa

The 2(2)Σ(+) and 4(2)Σ(+) excited states of (7)Li(40)Ca have been studied by high resolution Fourier-transform spectroscopy. The data on the lower state, 2(2)Σ(+), were obtained by analyzing the rotationally resolved spectra of the thermal emission of LiCa in the 2(2)Σ(+) → X(2)Σ(+) band around 9500 cm(-1). These data contained transitions mainly from v' = 0 and 1 for N' up to 92 and allowed us to derive molecular parameters describing the potential curve of the state close to its minimum. The dataset on the second state, 4(2)Σ(+), is much larger and comes from a laser-induced fluorescence experiment. The levels were excited by a single mode dye laser and the 4(2)Σ(+) → X(2)Σ(+) fluorescence was recorded through a Fourier-transform spectrometer. For both states potential energy curves and Dunham coefficients were derived and the spin-rotation structure was evaluated. The results are compared with theoretical and experimental data from the literature.

A study of the solvent temperature effects in a single longitudinal mode pulsed dye laser

The effect of the dye solution temperature in a single longitudinal mode pulsed dye laser pumped by a copper vapor laser was studied in detail. The study was carried out using a laser wavelength meter. It was experimentally observed that the wavelength tuning of the single mode dye laser with respect to the optical path length was limited to a grating pass band of 2.5 GHz beyond which a second mode appeared, a mode hop occurred and the laser wavelength settled at a new value. We observed cyclic behavior of single to two mode oscillation when the cavity length was changed continuously in one direction. The wavelength jitter band was observed to be ∼2.5 pm for two mode oscillation while it was ∼0.5 pm for single mode oscillation. By stabilizing the dye solution temperature to a set value of 20 ± 0.15 °C the cyclic behavior was eliminated and only a small drift of 1.4 pm was obtained over more than 30 min of operation. The wavelength change was attributed to variation of the optical path length due to variation of the refractive index with temperature. The cyclic behavior of single mode to two modes was established by applying voltage to the end mirror PZT, which changed the cavity length with a resolution of 8.5 MHz nm−1.

Operation of a CVL pumped dye laser in the single longitudinal mode and its parametric characterization

The parametric characterization of a high repetition rate (∼9kHz), indigenously developed, single longitudinal mode (SLM) dye laser based on a short Littman cavity and pumped by a copper vapor laser (CVL) is presented. The average bandwidth and the single pulse bandwidth have been measured to be ∼400MHz and ∼315MHz respectively for the SLM dye laser. Tunability of 12nm over 554–566nm has been achieved. The optimum dye concentration for minimum amplified spontaneous emission (ASE) has been determined experimentally for this SLM dye laser. The effect of pump power, grating diffraction efficiency, dye concentration on the buildup time of SLM and laser pulse duration has also been studied. The maximum buildup time was 15.5ns for SLM dye laser pumped by green CVL. The buildup time is reduced by nearly 25% with increase of pump power from 1W to 3W. The minimum build up time of 6ns was obtained with SLM dye laser pumped by second harmonic of Nd:YAG laser.

Electron affinity of selenium measured by photodetachment microscopy

The electron affinity ${}^{e}\phantom{\rule{-0.16em}{0ex}}A$(Se) of selenium is measured by photodetachment microscopy on a cesium-sputtering-produced Se${}^{\ensuremath{-}}$ ion beam using a single-mode CW dye laser. The measured value of the electron affinity is $16\phantom{\rule{0.16em}{0ex}}297.276(9)\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, or 2.020 604 6(11) eV, which improves the accuracy of this atomic quantity by a factor of 60.

Photodetachment microscopy to an excited spectral term and the electron affinity of phosphorus

A beam of P− ions produced by a cesium sputtering ion source was photodetached in the presence of an electric field, with a single-mode ring dye laser. Neutral P can be produced at one or the other of the fine-structure sub-levels of its 3s23p3 2Do excited term. This is the first atomic photodetachment microscopy experiment with excitation of the parent neutral atom out of the fundamental spectral term. The background electron signal due to ground-state photodetachment notwithstanding, photodetachment microscopy images produced at the excited thresholds could be analysed to provide a measure of these excited-term thresholds with interferometric precision. Starting from the three possible fine-structure sub-levels of P− 3s23p4 3P, the five fine-structure thresholds that may be detected, taking the selection rules into account, have been measured. They are combined with the spectroscopic data available in the literature on neutral P to produce an improved experimental value of the electron affinity eA of phosphorus: 602 179(8) m−1 or 0.746 607(10) eV. Taking all covariances of the optimized energy levels into account, one can merge them with the former measure of the three lowest detachment thresholds of P−, which results in a slightly more precise value of eA(P): 602 181(8) m−1, or 0.746 609(9) eV. The accuracy of eA(P) is now essentially limited by the uncertainty on the 2Do3/2 and 2Do5/2 energy levels of the neutral atom. The fine-structure intervals of the 3s23p3 2Do doublet of the neutral atom and of the 3s23p4 3P triplet of the negative ion have their accuracy improved by more than one order of magnitude.

Investigating the electronic states of BaOH by V-type double resonance spectroscopy and ab initio calculations: Further evidence of perturbation from the [formula omitted] state

A single band belonging to the A ∼ ′ 2 Δ - X ∼ 2 Σ + band system has been rotationally analyzed for each of the two isotopologues, BaOH and BaOD, using high-resolution V-type optical–optical double resonance spectroscopy. BaOH and BaOD molecules were synthesized in a Broida-type oven. High-resolution spectra were recorded by monitoring the dip in fluorescence of the B ∼ 2 Σ + - X ∼ 2 Σ + transition excited by a single-mode ring dye laser (pump laser), whilst a single-mode Ti:Sapphire laser scanned the corresponding A ∼ ′ 2 Δ - X ∼ 2 Σ + transition. The observed spectra resemble a typical 2 Π - 2 Σ transition, believed to emanate from single or triple quanta of the bending vibration in the A ∼ ′ 2 Δ state. Measured rotational lines have been assigned and rotational and fine structure parameters determined through a combined least-squares fit with the millimeter-wave pure rotational data of the X ∼ 2 Σ + state. Previous analyses of the A ∼ 2 Π - X ∼ 2 Σ + transitions of BaOH and BaOD yielded significantly different spin–orbit coupling constants, which were attributed to possible global and local perturbations arising from vibrationally-excited bands of the A ∼ ′ 2 Δ state. Although the newly observed A ∼ ′ 2 Δ state bands have not been conclusively assigned a specific spin state, the derived Ω-doubling constants show significant 2 Π 1 / 2 character, further indicating strong interactions between the A ∼ 2 Π and A ∼ ′ 2 Δ states of BaOH. To validate these conclusions, ab initio calculations have been carried out to further understand the nature of the BaOH excited states. The D ∼ ′ 2 Σ + , D ∼ 2 Σ + , C ∼ 2 Π , B ∼ 2 Σ + , A ∼ 2 Π , A ∼ ′ 2 Δ and X ∼ 2 Σ + states have been characterized by means of multireference configuration interaction calculations using the MOLPRO software. Calculated vertical term energies show relatively good agreement with existing optical data.

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.

Physics and technology of tunable pulsed single longitudinal mode dye laser

Design and technology demonstration of compact, narrow bandwidth, high repetition rate, tunable SLM dye lasers in two different configurations, namely Littrow and grazing incidence grating (GIG), were carried out in our lab at BARC, India. The single longitudinal mode (SLM) dye laser generates single-mode laser beams of ∼400 MHz (GIG configuration) and ∼600 MHz (Littrow configuration) bandwidth. Detailed performance studies of the Littrow and GIG dye laser resonators showed that GIG dye laser results in narrower linewidth and broad mode hop free wavelength scanning over 70 GHz. In this paper we present experimental studies carried out on the high repetition rate SLM dye laser system.

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.

Single mode coupled optofluidic ring resonator dye lasers

The authors demonstrate the single mode dye laser from a coupled optofluidic ring resonator that consists of a cylindrical ring resonator fused onto the inner surface of a thin-walled capillary ring resonator. The whispering gallery modes in each ring resonator interact strongly and utilize the Vernier effect to generate single mode laser emission. The lasing threshold is 3.0 μJ/mm2. The light can be coupled out through an optical taper in contact with the capillary.

Single-frequency and tunable operation of a continuous intracavity-frequency-doubled singly resonant optical parametric oscillator

A widely tunable continuous intracavity-frequency-doubled singly resonant optical parametric oscillator based on MgO-doped periodically poled stoichiometric lithium tantalate crystal is described. The idler radiation resonating in the cavity is frequency doubled by an intracavity BBO crystal. Pumped in the green, this system can provide up to 485 mW of single-frequency orange radiation. The system is continuously temperature tunable between 1170 and 1355 nm for the idler, 876 and 975 nm for the signal, and between 585 and 678 nm for the doubled idler. The free-running power and frequency stability of the system have been observed to be better than those for a single-mode dye laser.