An advanced commercial InfraRed Isotope Ratio (IR2) analyzer has been developed in Arrow Grand Technologies and the hollow waveguide (HWG) is used as the sample tube. By measuring the selected CO2 absorption peaks in the Mid- IR(MIR), the stable carbon isotope ratio, i.e. 13C, is obtained at a fast sampling rate. Combined with a GC and a combustor, it has been successfully employed to measure compound specific 13C isotope ratios in the field. By updating the single path HWG to 5-path HWG, we have also demonstrated its application for the environmental and health research. Here, the isotope ratio analyzer is minimized in size and weight to better fulfill the field deployment requirements. The size is reduced from 80cm*51cm*51cm to 74cm*33cm*46cm. After optimizing all subsystems, the minimized isotope ratio analyzer has a better performance. What’s more, the number of HWG paths can be selected to match the specific application. For instance, a 3-pass HWG is selected to conduct ultra-sensitive compound specific isotope analysis for mud gas logging, and a 5+1 pass HWG could measure isotope ratios of carbon with an ultra-broad CO2 concentration range of 300 ppm-47,500 ppm and a fast sample refresh and data processing rate up to 10Hz.
An advanced commercial Mid-InfraRed Isotope Ratio (IR2) analyzer was developed in Arrow Grand Technologies based on hollow waveguide (HWG) as the sample tube. The stable carbon isotope ratio, i.e. δ13C, was obtained by measuring the selected CO2 absorption peaks in the MIR. Combined with a GC and a combustor, it has been successfully employed to measure compound specific δ13C isotope ratios in the field. By using both the 1- pass HWG and 5-path HWG, we are able to measure δ13C isotope ratio at a broad CO2 concentration of 300 ppm-37,500 ppm. Here, we demonstrate its applications in environmental studies. The δ13C isotope ratio and concentration of CO2 exhaled by soil samples was measured in real time with the isotope analyzer. The concentration was found to change with the time. We also convert the Dissolved Inorganic Carbon (DIC) into CO2, and then measure the δ13C isotope ratio with an accuracy of better than 0.3 ‰ (1 σ) with a 6 min test time and 1 ml sample usage. Tap water, NaHCO3 solvent, coca, and even beer were tested. Lastly, the 13C isotope ratio of CO2 exhaled by human beings was obtained <10 seconds after simply blowing the exhaled CO2 into a tube with an accuracy of 0.5‰ (1 σ) without sample preconditioning. In summary, a commercial HWG isotope analyzer was demonstrated to be able to perform environmental and health studies with a high accuracy (~0.3 ‰/Hz1/2 1 σ), fast sampling rate (up to 10 Hz), low sample consumption (~1 ml), and broad CO2 concentration range (300 ppm-37,500 ppm).
The first of its kind Gas Chromatograph Infra Red Isotope Ratio (GC-IR2) instruments have been
deployed to the field to help the identification of sweet spot during the shale gas exploration. The onsite
measurement capability of the GC-IR2 along with its accuracy and speed helped the discovery of the fast
dynamics of gas release from shale cuttings. The half life of the isotope change for methane, ethane and
propane released from shale cuttings is closely related to the porosity and permeability of the specific shale
reservoir, and could be as short as a one hour to a couple of days. Initial δ13C values for methane could be
extremely fractionated toward heavy 13C species that values in the -20~<-10 per mil, which belong to
inorganic methane could be measured.
In our development of a field deployable infrared isotope ratio spectrometer (IR2) for compound
specific isotope analysis (CSIA), the IR2‘s accuracy and stability have reached a stage that small
fractionation in reference gas pulses generated as standard are observed easily and repeatedly. Such fine
fractionation is often difficult to observe in regular Isotope Ratio Mass Spectrometer (IRMS) due to
instrument drift on the order of 10s of minutes. After careful design of reference pulse sequences and long
period of data collection, such fractionations are also verified in a commercial continuous flow CSIA-IRMS.
Implications of the fractionation and observation process are discussed.
There have been limited choices of optical materials in the Mid-Infrared for polarization control and
subsequent isolation. We show several combinations of existing materials and optics that could realize
polarization control and isolation for quantum cascade lasers in the MIR. Improvements in signal to noise
ratio in MIR laser spectroscopy, as well as saturated absorption spectroscopy utilizing the isolation
achieved, will be discussed.
A field deployable Compound Specific Isotope Analyzer (CSIA) coupled with capillary
chromatogrpahy based on Quantum Cascade (QC) lasers and Hollow Waveguide (HWG) with precision
and chemical resolution matching mature Mass Spectroscopy has been achieved in our laboratory. The
system could realize 0.3 per mil accuracy for 12C/13C for a Gas Chromatography (GC) peak lasting as
short as 5 seconds with carbon molar concentration in the GC peak less than 0.5%. Spectroscopic
advantages of HWG when working with QC lasers, i.e. single mode transmission, noiseless measurement
and small sample volume, are compared with traditional free space and multipass spectroscopy methods.
To improve the Mid-Infrared (IR) chemical sensing capabilities in liquids and gases, a polymer
based waveguide that has 100% interaction with Quantum Cascade (QC) laser field is proposed and
demonstrated. The waveguide has thickness down to 10s nanometers so that chemical diffusion and
preconcentration could happen very fast; the path length is increased from several microns to over
centimeters due to the high spectral and diffraction brightness of QC lasers. Efficient prism coupling into
whispering gallery resonators' coated with submicron polymers and planar slab polymer waveguide are
demonstrated, high signal to noise ratio is obtained and potential applications discussed.
We present our results on efficient coupling of Quantum Cascade Lasers (QCLs) into Whispering
Gallery Resonators, Hollow Waveguide. We also present results of micro sensors using the unique
properties of QCLs, e.g. online sensors for Gas Chromatography (GC). We show that because of the
unique brightness properties of QCLs, we could improve GC-Infrared sensors' sensitivity to the same level
as Mass Spectrometry, and with different dimension of chemical information.
We show that QC laser could improve capillary Gas Chromatography Infrared spectroscopy
resolution significantly, i.e. both Doppler limited and Doppler free resolution could be achieved. To
achieve these goals, we report our latest efforts in characterizing the tuning and noise properties of
Quantum Cascade (QC) lasers; novel schemes on modulation to gain largest tuning range as well as on
stabilizing and locking the QC lasers are proposed, and results presented.
We show new results in modulating and modifying Quantum Cascade (QC) lasers to make them more
suitable for chemical sensing spectroscopy. Spectroscopy results using QC lasers are demonstrated with
whispering gallery mode CaF2 disc/ball, saturated absorption in hollow waveguide and direct chemical
analysis in water.
An amplifier design for broadband Mid-IR buried-hetero (BH) structure epitaxial laser is presented, and
external cavity design based on this amplifier is described. Spectroscopy results characterizing such single
frequency lasers are demonstrated with whispering gallery mode CaF2 disc/ball, saturated absorption in
hollow waveguide and direct chemical analysis in water.
Excitation of the whispering gallery modes (WGM) of a CaF2 ball resonator is demonstrated at 4.5 micron
with a pulsed Quantum Cascade laser. A prism coupling scheme for mid-infrared is described. Future
applications of WGM resonators as hyphenated inline chromatography sensors are discussed.
Gas monitoring over long distances using Frequency Modulation (FM) spectroscopy require phase insensitive detection scheme because of the severe scintillation problem. We report our effort to develop a long working distance CO2 monitoring LIDAR that uses phase insensitive Two-Tone Frequency Modulation (TTFM) spectroscopy technique. We could detect 10-4 single pass absorption, and could detect 1ppm CO2 level change in normal air.
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