Intracavity Laser Spectroscopy Research Articles

Intracavity laser spectroscopy with a semiconductor disk laser-pumped cw laser

Absorption spectra of the air have been measured near using intracavity laser spectroscopy with a semiconductor disk laser-pumped cw laser. It is shown that, at lasing times of at least , the sensitivity of the laser to intracavity absorption increases. This allows one to reach an effective path length of and enables detection of weak lines with absorption coefficients down to .

High-resolution four-photon intracavity laser spectroscopy with the external phase conjugation mirror

The phase conjugation regime is experimentally implemented in a cell with a liquid (water, ethanol, carbon tetrachloride) at the four-wave mixing of counter-propagating beams of diode lasers. Intracavity enhancement of the conjugate wave and the wave of the coherent anti-Stokes Raman scattering (CARS) arising in the interaction of the conjugate wave and one of the pumping waves in CARS scheme is detected. The latter process occurs in a narrow spectral range when the geometry of the wave vectors of the interacting waves in CARS scheme ensures arrival of the CARS signal at the laser aperture. It is found out that the quality of the four-photon phase conjugate mirror in the given interaction scheme is very sensitive to any perturbations (mechanical, acoustic, thermal, etc.) of the induced grating in the sample, which manifests itself in the distortion of the signal spectrum.

Analysis of the effect of small-scale inhomogeneities on the electrophysical characteristics of a thin layer by intracavity laser spectroscopy

A mathematical model is constructed, which makes it possible to vary the characteristic sizes of roughness, the electrophysical parameters of the biological sample under investigation, and its geometrical characteristics and to establish the relations between these parameters and biological properties of the biological tissue being modeled, as well as to calculate theoretically the absorption spectra of optically thin biological samples placed into the cavity of an optical resonator.

Photonic sensors review recent progress of fiber sensing technologies in Tianjin University

The up to date progress of fiber sensing technologies in Tianjin University are proposed in this paper. Fiber-optic temperature sensor based on the interference of selective higher-order modes in circular optical fiber is developed. Parallel demodulation for extrinsic Fabry-Perot interferometer (EFPI) and fiber Bragg grating (FBG) sensors is realized based on white light interference. Gas concentration detection is realized based on intra-cavity fiber laser spectroscopy. Polarization maintaining fiber (PMF) is used for distributed position or displacement sensing. Based on the before work and results, we gained National Basic Research Program of China on optical fiber sensing technology and will develop further investigation in this area.

Electronic spectra and molecular constants of zirconium mononitride

The electronic spectra and structure of zirconium mononitride were considered. The electronic vibrational-rotational spectrum of ZrN was obtained by intracavity laser spectroscopy within the 550–750 nm region. The spectrum was analyzed and the molecular constants of the ground X2Σ and excited A2Π electronic states were calculated. On the basis of the obtained experimental data and critical analysis of all the information on ZrN spectrum studies, the most reliable set of molecular constant values was recommended.

Spectroscopy of NiF by intracavity laser spectroscopy: Identification and analysis of the (1, 0) band of the [11.1] 2Π 3/2– X2Π 3/2 electronic transition

Spectroscopy of NiF by intracavity laser spectroscopy: Identification and analysis of the (1, 0) band of the [11.1] 2Π 3/2– X2Π 3/2 electronic transition

Intracavity laser spectroscopy for the identification of nanomedia

The optical absorption and emission spectra of heterogeneous plasma formations involved in the thermal synthesis of carbon-based nanomaterials have been studied. A characteristic relationship between parameters of the plasma-assisted synthesis of carbon nanotubes (CNTs) and the spectrum of giant Raman scattering is revealed. Operation of the intracavity laser spectroscopy setup in a near-field microscopy (tip-enhanced Raman spectroscopy) regime was observed. In this regime, a CNT formed in the laser plasma plays the role of a probe capable of enhancing the intensity of emission due to the Raman scattering.

Simulation of electrophysical properties of biological tissues by the intracavity laser spectroscopy method

A mathematic model is constructed for predicting the absorption spectrum and dispersion of a section of a biological structure consisting of epidermis, upper layer of the derma, blood, and lower layer of the derma and placed in the cavity of an optical resonator. The quantitative estimates obtained here can be used for predicting changes in the optical properties of the sample of the biological tissue under investigation associated with various biophysical and biochemical processes in this sample.

Spectroscopy of PtO by intra-cavity laser spectroscopy: Identification of the A 30 + – x1 electronic transition

Spectroscopy of PtO by intra-cavity laser spectroscopy: Identification of the A 30 + – x1 electronic transition

ICLAS of water in the 770 nm transparency window (12 746–13 558 cm −1). Comparison with current experimental and calculated databases

The absorption spectrum of water vapor has been investigated by intracavity laser spectroscopy (ICLAS) in the 12 746–13 558 cm −1 spectral region corresponding to an interesting transparency window of the atmosphere, partly obscured by the A band of molecular oxygen. The achieved sensitivity—in the order of α min∼10 −9 cm −1—has allowed one to measure 1062 water lines with intensities ranging from 1.6×10 −28 to 2.35×10 −24 cm/molecule at 296 K. A total of 169 new and improved energy levels belonging to 21 vibrational states could be determined from 374 newly measured transitions. The retrieved experimental line list is compared with the spectra calculated by Schwenke and Partridge, and Barber and Tennyson. Comparison with the available experimental databases shows that the obtained results represent a significant improvement of the knowledge of the water absorption in the considered region, in particular in the region of the oxygen A band.

Intracavity laser spectroscopy by using a Fe2+:ZnSe laser

A Fe2+:ZnSe laser emitting in the spectral range between 3.77 and 5.05 μm is used for the first time for intracavity laser spectroscopy. The intracavity absorption spectra of methane in the 4.1-μm region are recorded at different instants of lasing (0–80 μs) and the dynamics of spectral holes during lasing is investigated. It is found that an intracavity absorption signal linearly increases with time during lasing in the time range from 0 to 80 μs, which provides the effective absorption length up to 24 km.

Measurement of the coefficients of H2O absorption line shifts by intracavity laser spectroscopy

The results of measurement of H2O absorption line shifts induced by argon pressure are discussed. The measurements were made using an intracavity spectrometer based on a Nd laser. The estimations of possible half-widths and H2O line shifts in the range 1µm are reported, and the measurement procedure for the line shift coefficients by intracavity laser spectroscopy is developed.

Sensitivity calibration in intracavity laser spectroscopy

The possibility of sensitivity calibration in intracavity laser spectroscopy is investigated as applied to the measurement of the absorption kabs and gain kgain coefficients from lines with known kabs and kgain. The lines of a YAG:Nd3+ crystal placed inside the cavity of a basic Nd:glass laser were used as absorption and gain lines.

Spectroscopy of nickel chloride: Identification of the [15.0] 2Π 3/2 and [15.0] 2Δ 5/2 states

Vibrational bands belonging to the [15.0] 2Δ 5/2– A 2Δ 5/2, [15.0] 2Δ 5/2– X 2Π 3/2, and [15.0] 2Π 3/2– X 2Π 3/2 electronic transitions of NiCl have been observed in the 14 000–16 000 cm −1 region. The [15.0] 2Δ 5/2 and [15.0] 2Π 3/2 states are identified for the first time. The observed bands have been recorded at high spectral resolution using several techniques, which include intracavity laser spectroscopy (ILS), Fourier transform emission spectroscopy (FTS), and laser induced fluorescence (LIF) spectroscopy. For the ILS absorption spectra, NiCl molecules were produced in a nickel hollow cathode operated with a small amount of CCl 4. For the FTS emission spectra, excited NiCl molecules were produced in a King-type carbon tube furnace loaded with NiCl 2 and heated to 1600 °C. In the LIF work, NiCl molecules were produced by reacting laser-ablated nickel with PCl 3 seeded in argon. Detailed analysis of rotational transition lines indicates that the observed [15.0] 2Δ 5/2 and [15.0] 2Π 3/2 states are only separated by 10 cm −1 and are interacting with each other. Molecular constants for these newly observed electronic states are reported.

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.

Vapour growth of II‐VI single crystals doped by transition metals for mid‐infrared lasers

AbstractA modified vapour phase contact‐free method to grow homogeneous single crystals of II‐VI compounds doped by transition metals is presented. Single crystals of ZnSe:Cr, ZnSe:Fe, ZnSe:Co, ZnSe:Ni, CdSe:Cr, ZnTe:Cr, ZnS:Fe and ZnS:Mn with doping level up to 1019 cm–3 have been grown. Efficient lasing at about 2.5 and 4 µm with ZnSe:Cr and ZnSe:Fe crystals respectively has been achieved. Dependence of Fe2+:ZnSe laser characteristics on temperature is presented in more detail. A possibility of using Cr2+:ZnSe laser in intracavity laser spectroscopy is demonstrated. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Measurement of the O2 (b1Σg+ → a1Δg) transition probability by the method of intracavity laser spectroscopy

The method of intracavity laser spectroscopy using a Co:MgF2 laser is applied to record the absorption spectra from the first excited a1Δg state of gaseous molecular oxygen at the a1Δg → b1Σg+ transition at 1.91 μm. The gas flow from a chemical singlet oxygen generator with a known concentration of singlet oxygen O2 (a1Δg) was supplied to the cavity of the Co:MgF2 laser. The absorption line intensities are measured for five spectral lines of the Q-branch of the 0–0 vibrational band for the a1Δg → b1Σg+ transition. The O2 (b1Σg+ → a1Δg) transition probability calculated from these data was (1.20 ± 0.25) × 10-3 s-1.

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.

Spectral condensation near molecular transitions in intracavity laser spectroscopy with vertical external cavity surface emitting lasers

Vertical external cavity surface emitting lasers (VeCSELs) are ideal amplification media for intracavity laser absorption spectroscopy (ICLAS) around 1 μm. However, we noted that, in some spectra recorded by ICLAS-VeCSEL, the observed line profiles of very weak overtone transitions were clearly asymmetric, this distortion being more pronounced for the strongest lines. More spectacular effects were observed when we investigated the acetylene spectrum: while the weakest absorption lines appeared as dips superimposed on the baseline as usual in ICLAS, the strongest lines mostly disappeared and were replaced by emission lines slightly blue shifted from the absorption line center. This effect, called “spectral condensation”, was, in fact, discovered near atomic transitions, more than 30 years ago, using pulsed lasers. Using acetylene and water as absorbers, we have systematically studied the different factors of importance for spectral condensation and showed that it increases with the pumping rate, the generation time and the line intensity. Spectral condensation was also found to increase with the pressure of the intracavity gas sample up to a value of a few Torrs, and to decrease afterwards. The appearance of spectral condensation has been shown to be highly correlated to time oscillations of the total laser power. Of importance for intensity measurements, this systematic study has showed that condensation effects may appear for long generation times even at low pumping rate and even with extremely weak absorption lines. A discussion of the results in relation with different interpretations available in the literature is presented with a particular emphasis on the theory based on the coherent interaction of electro-magnetic field with optically dense resonant extended medium leading to a parametrical amplification without population inversion.