The investigation of the volume and composition of industrial aerosol-gas emission is of interest in two aspects:
* the study of regional ecological impacts of imperfection of the present-day industrial technologies because the emissions determine the quality of life of population residing the territory exposed to the emission;
* the consideration of global consequences of industrial public activities including a probable change of climate owing to the disturbance of the radiation balance of the system "the underlying surface-the atmosphere".
The chemical composition and physical conditions in the aerosol-gas emissions can be unacceptable for reliable operation of contact sensors when instrumental testing. Under these conditions, for the monitoring of the emissions, it is necessary to use the remote sensing elements, in particular, optical ones.
The report presents the results of the development of two pilot Raman lidars as the means for remote analysis of the aerosol-gas emissions. The advantages of the Raman lidars are in their possibility to obtain the data on a great quantity of gases using one laser as well as to conduct their metrological attestation as teh meters (that is presently impossible for aerosol lidars).
The total ozone amount (TOA) is determined as a rule by classic spectrophotometric method: TOA is found from a measured difference of the atmospheric optical thicknesses at two specially selected wavelengths in the region 305-340 nm. In this region the aerosol and molecular scattering takes place and it is traditionally believed, that the molecular absorption in this spectral region is conditioned only by ozone. Researches performed in the Institute of Atmospheric Optics SB RAS at the end of 1980s have shown, that there is also gentle absorption of a water vapor in this region, which can make a contribution to the measured difference of atmospheric optical thicknesses and can result in some methodical error. Thus, the TOA value which is determined without considering the water vapor, may be overstated.
The analysis of interaction between the ground X1A1 and excited B1A1 electronic states of the water molecule have been made and it was shown that the centrifugal distortion near the linear HOH configuration may lead to a considerable state mixing in the case when both lower and upper state wave functions are localised near linear configuration. As a result, transitions to the high-bending states, such as (0V20) with V2~20, within the ground electronic state may be intense due to intensity borrowing. This effect appears to explain the weak 0.27 mkm feature in the near UV water vapor spectrum observed early experimentally.
Basic principles of weak echo-signals laser receiving are briefly summarized and autodyne lidars employing this way of weak signal detection while sounding the atmosphere are described. Detection of weak light signals by a hybrid laser is studied theoretically and experimentally. Autodyne lidar modifications, namely the multipurpose cw parametric autodyne lidar which allows one to increase a set of retrieved from the received by the laser echo-signal optical and dynamic characteristics of an atmospheric path and a remote retroreflector and a hybrid lidar in which positives of conventional cw autodyne lidars are combined with those inherent to pulsed lidars are discussed
The method of broad-band Intracavity Laser (ICL) Spectroscopy suggested in 1970 [1] consists of quenching the laser emission at the absorption-line frequencies of the species placed in a broad-band laser cavity, the generation band width of such a laser being much greater than the half-width of spectral line studied. In this case the laser emission spectrum has sharp dips at the frequencies of absorption lines, which can be recorded with an ordinary spectroscopic instrumentation. In the intracavity laser spectroscopy a laser itself is a nonlinear detector of a weak absorption and therefore the parameters of an intracavity spectrometer are first of all determined by the mechanism of the lasing process. The most important are the resonator mechanism caused by multipass travelling of radiation during the process ofgeneration and the threshold character oflasing process. The models describing the formation of a dip in the laser generation spectrum [2-8] can be divided into two groups. The first one asumes high sensitivity of the ICL-spectrscopy to be due to the threshold mechanism for which it is supposed the laser system is in a stationary stable state and all the parameters determining the sensitivity of the intracavity absorption are constant in time [7-8]. These models predict a strong influence of the spatial inhomogeneity of the inversion decay and a sharp increase of the ICL-spectrometer sensitivity near the generation threshold. The second group of the models is based on the assumption that even cw multimode lasers never reach a stable state of generation due to its breaks at a mode caused by different perturbation mechanisms, the life time of a mode being the basic quantity which determines the ICL-spectrometer sensitivity (so called resonator mechnism). Time sweep of the laser emission spectra confirm the fact that longitudinal modes of a cw laser have a fmite life time [9]. The analysis ofFourier spectra ofsuch a laser has revealed that at high spectral power density single modes oscillate at about 100 kHz frequency which corresponds to a 10 ts lifetime of a mode [10]. The decrease of the spectral power density results in the increase of a mode's lifetime, that in turn causes the increase of the ICLspectrometer sensitivity near the generation threshold. Experiments carried out under careftilly controlled conditions showed that the depth of a dip in the intracavity spectrum increases exponentially with the increase of mode's life time.9 This convicingly shows the validity of the resonator mechanism. The resonator mechnism allows one to explain the possibility of recording absorption coefficients as low as Kmin 1010...l01 'cm' during a 0.1 s time interval. As has been shown in Ref. 1 1 detection limit of ICLspectrometer based on broadband ranning wave dye laser is determined by quantum nature of radiation. However, it is only possible if the frequency variations of the laser gain coefficient in the vicinity of an absorption line is less than Kmin. The spectral stability of the gain coefficient is, in turn, determined by the broadening mecahnism in the active medium, i.e. by the ratio ofthe width ofhomogeneous amplification contour (or frequency filter width in resonator) to an absorption line halfwidth. The simplest way of excluding the frequency variation of gain coefficient is decreasing of the numbers of resonator optical elements. In that case the resolnator scheme becomes very simple and consists of 2 mirrors and an active element. Simultaneously, such simplicity decreases the spectral range of the spectrometer, so generation band covers only 20-30% ofgain profile width. The increase ofthe spectral tunable region using dispersive resonator leads to decreasing of the spectrometer sensitivity, so a scheme of the resonator of the ICL-spectrometer is determined by concrete task of investigation. Begining from 1970 the method of ICL-spectroscopy has been extensively developing and now there are about 500 papers in this field including several reviews13'7, devoted to the analysis of sensitivity of ICL-spectroscopy to the determination of quantitative information and to use of different schemes of the spectrometers. There was comprehensive analysis of the ICL-spectrometers for the aim of obtaining quantitative information performed at the Institute of Atmospheric Optics beginning 1972 when first ruby laser ICL-spectrometer had been designed here.12 It includes: 1) design of a complex of ICL-spectrometers based on Nd-glass, ruby, dye, and color 22 center lasers; 2) determination of absorption line parameters; 3) development of efective methods for elimination of spurious selection; 4) use of dispersive resonator in ICLspewometers. Obtained results were summarized in the monograph "Intracavity laser spectroscopy. Method and application" which was published in Russian in 1985. ' This monograph is the only monograph on Intracavity laser spectroscopy in the world but scientists abroad the Russia practically have no information on it. In this paper the main materials of the monograph are presented and the last results in ICLspectroscopy obtained at the Institute of Atmospheric Optics and at others scientific centers during last 10 years are su.mmurised.
Excimer lasers with stimulated Raman scatteiing cell and Nd YAG laser with frequency doubler were employed to study the effect oflaser radiation both on intact and atheroscierotically damaged aortic wall. After inadiation,, samples of aorta were subjected to detailed morphologic study and sizes of craters, necrosis and tissue destruction zones were determined. Lipid content and spectra of the extracts affected by laser beam were under consideration as well.
Key words: laser angioplasty, tissue ablation, photodissociation ofbiological molecules
A set of laboratory experiments was performed to study a possibility of selective laser action on different classes of atherosclerotic plaques and samples of normal vessel walls were performed. To this end Nd:YAG-laser with frequency doubler and quadrupler as well as XeCl-laser with SRS cell were employed which allows us to compare results of laser action in broad spectral range. The laboratory setups permit us to vary parameters of laser radiation, such as the pulse duration, energy and density of the energy in process of experiments. All samples were subjected to detailed morphological study. Experiments performed indicate the possibility of initiation of photochemical destruction of plaques by UV laser radiation. Such a possibility is supported also by semi-empiric quantum chemistry calculations performed for fat acids. All this allows us to suggest a sort of optimal strategy for laser destruction of atherosclerotic plaques with minimal site effects.
To study a possibility of selective laser action on atherosclerotic plaques and normal vessel wall a set of laboratory experiments was performed. We used XeCl-laser with a Raman shifting cell and Nd-YAG laser with a frequency doubler, tripler, and quadrupler. It allows us to compare the results of laser action on tissue in a broad spectral range. The laboratory setups permit us to vary parameters of laser radiation such as pulse repetition rate, duration, energy, and power density. All samples were subjected to detailed morphological study. In particular, experiments with XeCl-laser demonstrate that the specific vaporization energy decreases when the laser energy increases. The penetration depth of laser radiation was considerably less than is to be expected from the measurement of absorption factor at 308 nm. Moreover, the absorption spectrum of the tissue after irradiation was absolutely different from the initial tissue absorption spectrum. Therefore, the two-photon processes play the main part in the interaction of high-power laser-light with tissue. Thus the laser pulse duration is to be considered as one of the most important parameters in this case. It is shown also that IR radiation at 1.06 mkm is quite effective to penetrate into calcified plaques. Laser angioplasty is still to be considered as a promising technique for treatment of vascular diseases. However, the discussion about the type of laser to be used for this purpose has not yet been finished.
Intracavity laser spectroscopy (ILS) presents itself as a highly effective technique that allows one to detect the change of light signal from absorbing molecules at a level of radiation quantum noise. Thus high sensitivity of ICLS allows one to determine the absorbing molecules concentrations in gases and liquids in the range between 10-6 to 10-10. The potential of ICLS technique employment for establishing interrelations between small changes in the breathed air caused by diseases in the early stage, as well as a mass screening of patients with diseases of the liver and kidneys by acetone and urea detection in breathed air, and with heart diseases by measurement of CO2 concentration is discussed. Usage of gas, dye and solid-state lasers for such measurements is analyzed, optimum spectral ranges are presented.
A novel approach to imagination of inner surface of arteria during performing laser and balloon angioplasty is suggested. To this end the laser light was transmitted via fiber to the zone of interest and radiation diffused by the walls of the vessel was adopted by receiver. Known technique to determine of contours of an object by measuring the time of the laser pulse propagation is unusable due to the small geometrical scales. Using the CW laser and feeding a portion of the backscattered signal power into the laser cavity (this kind of device was referred to as laser autodyne coherent receiver), the authors have been able to measure the object contour with spatial resolution of up to 2 microns. Such resolution and high sensitivity inherent to this technique should allows one to detect early in the development of the atherosclerosis. To obtain the 3D image of the vessel inside surface we offer two methods. In the first case the vessel side is scanned by moving the end of light quid. In the second one multimode laser is used and the image is drawing by scanning the transverse modes of this laser. The vessel side and atherosclerotic plaques have the different reflectivity spectrum and this fact can be used to increase the image contrast. The correct selection of the laser wavelength makes possible to work into the vessel with circulation of the blood. The calculation of laser autodyne intrascope performance and tentative experimental results are presented in this report. The advantages of this method for the angiography are in speed and adequately of control during performing angioplasty.
Since the late 1960s atherosclerotic plaque (AP) laser ablation techniques have been developed. Clinical data obtained with CW laser vaporization AP shows significant impairment of tissues close to plaque with following severe complications in postoperation period. The use of excimer pulsed laser decreases the harmful effects of laser radiation. However, data on spectrum of energy absorption by molecular AP structures are required for selective photodynamic action of UV laser emission. The aim of the present study is to estimate IR and UV absorption and fluorescence spectrum of intact and atherosclerosis-induced changes in aorta and brachiocephalic trunk. Autopsied vessel specimens with artery decease were analyzed. Absorption spectrum of frozen vessel slices (15 micrometers ) and oil emulsion was recorded. Characteristic absorption bands in 3000 cm-1 were noted as for AP as for intact tissue. In 1700 cm-1 AP IR spectrum has an absorption band which is not seen in normal tissue spectrum. Reflection spectrum of intact vessel wall surface and AP at range 45000 to 11000 cm-1 was recorded as well. In 32000 cm-1 reflection was 66% and 43% for AP and intact tissue, respectively. At range 17000 to 13000 cmMIN1 curve position is changed: reflection for AP-66%, for intact wall-93%. Thus, reflection, absorption and fluorescence spectrum of intact and atherosclerotic vessels vary significantly. It provides us with a basis for intravessel examination and selection of laser parameters for harmless endovascular surgery.
This paper reviews the results of laser absorption, fluorescence spectroscopy instrumentation, and methods development at the Institute of Atmospheric Optics during the last 15 years and their application to problems of local gas analysis.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.