Intracavity Absorption Research Articles

Semiconductor laser with extended cavity and intracavity atomic filter

We report on peculiar dynamic features of laser oscillation in a cavity with a semiconductor junction as the gain medium and an intracavity atomic absorber. The output face of the semiconductor is antireflection coated, and lasing action is achieved by using a diffraction grating to close the laser cavity. The spectral analysis of the laser emission evidences a stable emission with narrow linewidth when the oscillating frequency is resonant with the atomic absorber. We also observe frequency bistability and instability. The change between these regimes is controlled through the bias current in a very reproducible way.

Continuous-wave 155 μm diode-pumped surface emitting semiconductor laser for broadband multiplex spectroscopy

A room-temperature-operating vertical external cavity surface emitting laser is applied around 1550 nm to intracavity laser absorption spectroscopy analyzed by time-resolved Fourier-transform interferometry. At an equivalent path length of 15 km, the high-resolution spectrum of the semiconductor disk laser emission covers 17 nm simultaneously. A noise-equivalent absorption coefficient at 1 s averaging equal to 1.5×10−10 cm−1Hz−1/2 per spectral element is reported for 65 km, the longest path length employed.

Intracavity laser absorption spectroscopy of AuO: Identification of the b4Π 3/2– X2Π 3/2 transition

The visible electronic spectrum of AuO has been recorded at rotational resolution using intracavity laser absorption spectroscopy. Five vibrational bands have been analyzed and assigned as the (0, 0), (1, 0), (2, 0), (3, 0), and (4, 0) bands of the b 4Π 3/2– X 2Π 3/2 transition of AuO. The molecular parameters for the newly identified b 4Π 3/2 state are presented.

Real-time, ultralow concentration detection of analytes in solution by infrared intracavity laser absorption

Two intracavity laser absorption techniques for ultralow concentration detection of chemicals in solution are compared. The first consists of a laser diode in a grating extended cavity, which produces a linear calibration curve for parts in 10(9) (ppb) concentrations corresponding to 17 nM. By replacing the grating with a highly reflective mirror, parts in 10(12) (ppt) concentration detection is achieved, which corresponds to 340 pM. We report, to our knowledge for the first time, ppt detection of analyte concentration in liquid solution demonstrating good agreement between theory and experiment.

Intra-cavity absorption spectroscopy with narrow-ridge microfluidic quantum cascade lasers

We demonstrate microfluidic laser intra-cavity absorption spectroscopy with mid-infrared lambda approximately 9mum quantum cascade lasers. A deepetched narrow ridge waveguide laser is placed in a microfluidic chamber. The evanescent tails of the laser mode penetrate into a liquid on both sides of the ridge. The absorption lines of the liquid modify the laser waveguide loss, resulting in significant changes in the laser emission spectrum and the threshold current. A volume of liquid as small as ~10pL may, in principle, be sufficient for sensing using the proposed technique. This method, similar to the related gas-phase technique, shows promise as a sensitive means of detecting chemicals in small volumes of solutions.

Fiber laser intracavity absorption spectroscopy of ammonia and hydrogen cyanide in low pressure hydrocarbon flames

Fiber laser intracavity spectroscopy (FLICAS) with Er-doped fiber laser has been applied for the first in situ detection of ammonia and hydrogen cyanide in a low pressure (30 Torr) stoichiometric methane/nitrogen/oxygen flame doped with 0.13–1.36% of NH 3. High resolution spectra of NH 3 and HCN have been recorded in the range of 1.5 μm (6440–6540 cm −1). The minimum detectable concentration of HCN and NH 3 at a laser pulse duration of 8 μs and room temperature is 1 × 10 13 molecule/cm 3. The method can be used for in situ detection of many other molecules in the hostile combustion environment.

Broadband Cavity Ringdown Spectroscopy for Sensitive and Rapid Molecular Detection

We demonstrate highly efficient cavity ringdown spectroscopy in which a broad-bandwidth optical frequency comb is coherently coupled to a high-finesse optical cavity that acts as the sample chamber. 125,000 optical comb components, each coupled into a specific longitudinal cavity mode, undergo ringdown decays when the cavity input is shut off. Sensitive intracavity absorption information is simultaneously available across 100 nanometers in the visible and near-infrared spectral regions. Real-time, quantitative measurements were made of the trace presence, the transition strengths and linewidths, and the population redistributions due to collisions and the temperature changes for molecules such as C2H2, O2, H2O, and NH3.

High sensitivity absorption spectroscopy of HDO by ICLAS-VeCSEL between 9100 and 9640 cm −1

The absorption spectrum of monodeuterated water has been recorded between 9100 and 9640 cm −1 using intracavity laser absorption spectroscopy (ICLAS) based on a vertical external cavity system emitting laser (VeCSEL). Overall 1706 lines were attributed to the HDO species. The spectrum assignment was performed on the basis of the ab initio calculations by Schwenke and Partridge. A set of 746 energy levels was derived from transitions assigned to 13 upper vibrational states, 300 of them being reported for the first time. Resonance interactions leading to an important strengthening and observations of the very weak 7 ν 2 and ν 1 + 5 ν 2 bands are discussed. A detailed line list has been generated.

Intracavity Cr4+ :YAG laser absorption analyzed by time-resolved Fourier transform spectroscopy

A high-resolution time-resolved Fourier transform interferometer is combined with a multimode Cr4+:YAG laser for intracavity laser absorption spectroscopy (ICLAS) experiments. Atmospheric absorption spectra are recorded in the 1.5 μm region with a minimum detectable absorption coefficient equal to 8×10-11 cm-1 Hz-1/2. The broad gain bandwidth of the crystal allows a simultaneous spectral coverage at most equal to 38 nm. The laser tunability covers the 1360–1577 nm range. Water vapor detection domain extends from the 100 ppmv down to the 0.1 ppbv level.

Absolute line intensity with FT-ICLAS: 12C 2H 2 near 12 800 cm −1

We have used a Fourier transform intracavity laser absorption spectrometer to measure the absolute intensity of lines in the ν 1 + 3 ν 3 band of 12C 2H 2 at 12675 cm −1. Under optimal conditions the agreement is found to be within 5% of reference values measured by conventional Fourier transform spectroscopy [F. Herregodts et al., Mol. Phys., 101 (2003) 3427]. The absolute intensity of 21 weaker lines not experimentally investigated in the latter work, is listed. Various tests of the instrumental method are presented, also demonstrating its ability to determine pressure self-broadening coefficients.

Si H 2 Cl 2 : Ab initio anharmonic force field, dipole moments, and infrared vibrational transitions

The vibrational spectra of SiH2Cl2 have been recorded in the 1000-13,000 cm(-1) region, utilizing the Fourier-transform spectroscopy and Fourier-transform intracavity laser absorption spectroscopy. Totally 61 band centers and intensities are derived from the infrared spectra. An ab initio quartic force field is obtained by applying the second-order Moller-Plesset perturbation theory and correlation-consistent polarized valence triplet-zeta basis sets [J. Chem. Phys. 90, 1007 (1989); 98, 1358 (1993)]. Most observed bands are assigned by the vibration analysis based on the second-order perturbation theory. Reduced-dimensional ab initio dipole moment functions (two dimensional and three dimensional) have also been calculated to investigate the absolute band intensities of the SiH2 chromophore. The calculated values agree reasonably with the observed ones.

Spectral dynamics of intracavity absorption in a pulsed Cr2+:ZnSe laser

The growth dynamics of intracavity absorption is studied during recording line absorption spectra by the method of intracavity laser spectroscopy using a pulsed Cr2+:ZnSe laser tunable between 2.1 and 3.1 μm. In the lasing duration range from 0 to 235 μs, an intracavity absorption signal increases linearly with time, providing the effective absorption length of 70km.

Frequency shifts in a stabilised laser due to reflection of radiation from extracavity optical elements

The effect of radiation reflected from an external optical element on the performance of a stabilised laser with an intracavity absorption cell is studied experimentally and theoretically taking into account the nonlinear frequency pulling to the absorption line centre.

Discharge−Flow Kinetics Measurements Using Intracavity Laser Absorption Spectroscopy

Intracavity laser absorption spectroscopy ("ICLAS") has been demonstrated as a feasible detection method for trace species in a discharge flow tube. This implementation has been used to measure the rate of the reaction between atomic hydrogen and NO to form HNO in helium carrier gas. A reaction rate constant of (4.3 +/- 0.4) x 10(-32) cm(6) molecule(-2) s(-1) at 295 K was measured for the reaction H + NO + M --> HNO + M (M = He). The pressure and concentration range enabled by ICLAS detection has allowed us to limit reactive pathways that would inhibit the formation of HNO. The sensitivity of ICLAS, coupled with the versatility of the discharge flow technique, suggests that intracavity absorption spectroscopy will be a useful technique for kinetics measurements on free radicals and other reactive species.

New combination bands in 12C 13CH 2 around 0.83 μm recorded using FT-ICLAS

Fourier-transform intracavity laser absorption spectroscopy allowed five 12C 13CH 2 Σ +–Σ + bands, all from the ground state, to be identified in the 0.83 μm range. Their rotational analysis was performed and rotational constants are provided. Three of these bands, with origins at 11616.9684(18), 11737.2356(14), and 11761.0322(23) cm −1, have never been reported before. Their upper states are assigned to v 1 v 2 v 3 v 4 l 4 v 5 l 5 = 1302 0 2 0 , 1301 1 3 - 1 , and 2201 1 1 - 1 , respectively.

Resonance spectrum and dissociation dynamics of ozone in the 3B2 electronically excited state: experiment and theory.

The rovibrational spectrum assigned to the low-lying (3)B(2) electronic state of ozone is measured with intracavity laser absorption spectroscopy. The experimental results are interpreted by means of quantum dynamical calculations on a global ab initio potential energy surface. The observed spectrum is shown to originate from the vibrational ground state in the local minimum of the (3)B(2) potential. The spectrum of short-lived resonance states in this local minimum is analyzed. Additionally, the global minimum of the surface is shown to lie in the dissociation channel in the van der Waals region. This region supports a short sequence of weakly bound vibrational states.

High-resolution Fourier-transform intra-cavity laser absorption study of H 12C 13CH and H 13C 13CH at around 12 600 cm −1: a case of strong anharmonic resonances

Fourier-transform intra-cavity laser absorption spectroscopy has been used to record high-resolution vibration–rotation overtone spectra of carbon-13 substituted acetylenes, H 12C 13CH and H 13C 13CH, in the third CH stretching overtone region between 12 500 and 12 730 cm −1. The observed spectra of both species contain only parallel bands for which rovibrational spectroscopic parameters have been determined. Several anharmonic resonances have been identified and rotationally analysed using traditional vibration–rotation theory. Altogether six bands, which include ν 1 + 3 ν 3 and 4 ν 3 for H 12C 13CH and ν 1 + 3 ν 3 for H 13C 13CH, have been observed for both species. Four of the six bands in each molecule are reported for the first time.

Development of fibre laser systems for ring-down and intracavity gas spectroscopy in the near-IR

We describe our progress in the development of intracavity systems with erbium fibre lasers using ring-down or intracavity laser absorption spectroscopy. Ring-down times have been extended out to several milliseconds and digital signal processing techniques introduced for removal of unwanted spectral components from the data and for display of the attenuation history. The theoretical sensitivity limits for intracavity absorption spectroscopy are discussed for a three-level laser, taking into account ground state absorption, and about three orders of magnitude enhancement in effective path length is expected. A detailed analysis has been performed on the relaxation oscillations induced during the transient operation of the laser with the aim of monitoring laser parameters and for the future development of an interrogation system for the capture of modal spectra in the presence of intracavity absorbers.

Triple-Mode Action of a Broad-Band Laser from the Viewpoint of Intracavity Frequency-Dispersion Spectroscopy

For the beat spectrum of a triple-mode dye laser, there exists a component with a frequency equal to the difference in intervals between adjacent modes. The correlated technical fluctuations of these intervals compensate each other. This experimental fact is considered as promising for the development of a new spectroscopy method with a detection limit of the order of 10-10–10-11 cm-1 with respect to absorption in the probing volume. It is based on different changes in adjacent-mode intervals due to dispersion of the resonance line of the intracavity absorber. Thus the low frequency signal appearing in the beat spectrum can be detected. The latter is proportional to the density of absorbing particles.

Intracavity laser spectroscopy using a Cr2+ : ZnSe laser

A Cr2+ : ZnSe laser emitting 100-μs pulses tunable in the 2–3-μm region is used for the first time for the highly sensitive detection of absorption spectra by the method of intracavity laser spectroscopy. The intracavity absorption spectra of the atmospheric air were recorded at different instants of lasing in the spectral region from 2.41 to 2.46 μm. An increase in the sensitivity of the laser emission spectrum to intracavity absorption was observed over the entire range of lasing durations studied.