以二氧化碳雷射光聲光譜法來偵測微量氣體的方法在過去已被廣泛地運用，包括汽機車及工業排放的廢氣檢測、大氣中的稀有氣體偵測及農作物的生長監測等。近年來，以雷射紅外光譜偵測微量氣體的技術更被應用到各種生物及醫學用途，如動植物(包含人體)的呼吸檢測、醫療診斷以及生化反應的監控等。其中亦不乏以二氧化碳雷射當作激發光源，透過相關反應物的偵測來完成其定性或定量分析，這些研究指出了二氧化碳雷射光聲光譜技術開發新應用的潛能。

本研究成功建置一套二氧化碳雷射光聲光譜量測系統，該系統可自動化測量各種氣體樣品之吸收光譜。二氧化碳雷射是採用射頻激發放電式的波導結構。相對於傳統開放式的光學共振腔雷射而言，波導式共振腔可以更有效利用放電區域增益介質，提高單位長度雷射增益並縮小整個雷射的體積；而射頻激發放電則可以避免使用高電壓設備，延長器件壽命並提升放電效率。由於它可以操作在較高的氣壓下，如此可增加雷射線寬並提高其與氣體吸收譜線的重合機率，適合作為光聲光譜儀之激發光源。至於光聲氣室的設計，我們嘗試使用一個簡單小巧的非聲波共振式結構來實現高靈敏度的偵測，方法是將該氣室置於雷射共振腔中，透過增強的雷射功率來提昇氣體吸收的能力。

除量測系統的建立外，本研究亦提出幾種可能的應用。首先，我們注意到此方法可用於酒精飲料之檢測。藉由測量純甲醇與純乙醇水溶液的吸收光譜，再依據各吸收譜線之吸收係數大小與吸收係數對比，並考量量測動態範圍與雷射的穩定性，建立了三條校正線。接著我們配置不同乙醇濃度的酒精溶液來模擬市面上常見的酒精飲料，再分別混合少量甲醇於其內。透過該吸收光譜與先前的校正曲線可以計算溶液中的甲醇與乙醇含量，並與理論值比較，有相當程度的吻合(誤差 < 5.89%)。此結果顯示二氧化碳雷射光聲光譜法的確有其可行性。相同的方法可以運用到一些揮發性有機化合物的偵測上，例如汽油添加甲醇的檢驗、水質偵測(汽油污染)、丙酮污染與監測、甚至酒駕執法所需的酒精濃度檢測等。相對於傳統的氣相層析法，我們的方法具有快速、簡單且成本低等優勢；相對於電化學式氣體感測器，我們的方法則能提供較準確與多種元素的分析。這些初步的實驗將有助於未來進一步研究的參考。

The CO2 laser-based photoacoustic (PA) spectrometry has played an important role in a wide variety of applications, such as the detection of motor-vehicle and industrial exhausts, air pollution monitoring, trace gas sensing in the growth of plants, and so forth. With development of laser-spectroscopic gas sensors, the infrared gas analysis techniques are attracting lots of interest in medicine and biology in recent years. These include breath analysis for animals or human beings, medical diagnostics, and biological processes in living organisms, etc. For some specific molecular species, the use of CO2 laser PA method was still proven to be valuable in sensitivity and multi-component analysis. The successful examples of CO2 laser PA detection may imply the possibilities for future potential applications.

This thesis reports the construction of an automatic CO2 laser PA spectrometer which uses a RF-excited waveguide CO2 laser. Operating in a waveguide mode can obtain higher gain per unit length, reduced physical size, and larger linewidth, thus increasing the probability of overlap between laser transitions and gas absorption spectrum. RF excitation provides additional advantages of low-voltage operation, improved lifetime and better overall efficiency. To increase the sensitivity, we put the small PA cell inside the laser cavity while operating in nonresonant mode.

In addition, a number of new applications for trace-gas detection by CO2 laser PA spectrometry have also been proposed in this study. The use of this PA method for detecting the methanol contents in alcohol beverages is first presented. The calibration curves for methanol and ethanol were established by selecting three laser transitions. A series of samples referring to adulterated alcoholic beverages were measured and the concentrations of methanol and ethanol could be derived by the PA spectra. These results show great promise for diagnosis of adulterated wine by using CO2 laser PA spectrometry (error < 5.89%). This idea can be applied further for the detection of some volatile organic compounds, such as methanol/gasoline blends, gasoline contamination in water, acetone pollution, and even alcohol breath analysis. Compared to traditional gas chromatography, the PA scheme provides fast and easy operation without pre-treatment of toxic chemicals. Also, the spectroscopic method offers reliable and multi-component analysis in comparison with common chemical gas sensors. The preliminary measurements can be an experimental reference for future work.

Chapter 1 Introduction 1
1.1.Overview………………………………………………………. 1
1.2.Historicalreview……………………………………………. 2
1.3.Organization of the dissertation …………………….. 5

Chapter 2 Fundamentals of Photoacoustic Spectroscopy 7
2.1.Generalreview……………………………………………… ..7
2.2.Light absorption and heat release………………… ... 8
2.3.Acoustic and thermal wave generation…………………..10
2.4.Acoustic signal detection………………………………...13
2.5.Cell design…………………………………………………… 15
2.6.Trace gas analysis…………………………………………. 17
Figure 2.1-5……………………………………………………… 21

Chapter 3 Principles of CO2 laser photoacoustic spectrometry 25
3.1.Overview…………………………………………………….. 25
3.2 RF-excited CO2 waveguide laser……………………….. 26
3.3 Wavelength tuning machanism……………………………. 28
3.3.1 Line selection using a grating………………….. 28
3.3.2 Stepping motor control………………………..... 31
3.4 Photoacoustic detector………………………………….. 32
3.4.1 Capacitive microphone……………………………… 32
3.4.2 PA cell……………………………………………….. 33
3.4.3 Gas handling system………………………………… 33
3.4.4 Lock-in amplifier……………………………………. 34
3.5 Signal process equipments…………………………….... 35
3.6 PA spectroscopic method for gas analysis ………... 37
Figure 3.1-12 ……………………………………………….... 39

Chapter 4 Detection of methanol in alcoholic beverage with
CO2 laser photoacoustic spectrometry 49
4.1 General review…………………………………………….. 49
4.2 Materials and methods…………………………………….. 50
4.2.1 Sample preparation………………………………….. 50
4.2.2 Establishment of calibration curves……………. 51
4.2.3 PA measurements and analysis……………………… 52
4.3 Experimental results………………………………………. 52
4.3.1 Methanol……………………………………………….. 52
4.3.2 Ethanol…………………………………………………. 53
4.3.3 Mixture of two-component alcohol………………. 54
4.4 Discussion…………………………………………………… 56
4.4.1 Saturation of PA signal…………………………… 56
4.4.2 Laser frequency instability………………………. 57
4.4.3 Calibration of the laser wavelength……………. 57
4.4.4 Background signals…………………………………. 58
Figure 4.1-7……………………………………………………… 59
Table 4.1 Detected and nominal concentrations for the two-component mixture of methanol and ethanol……………... 66


Chapter 5 Potential applications for the detection of some
volatile organic compounds (VOCs) by CO2 laser PA spectrometry 67
5.1 Overview………………………………………………………. 67
5.2 Methanol in gasoline blends……………………………….68
5.2.1 Motivation……………………………………………...68
5.2.2 Experimentals…………………………………………..69
5.3 Gasoline contamination in water……………………….. 72
5.4 Acetone contamination……………………………………….74
5.5 Alcohol breath analysis…………………………………… 75
Figure 5.1-11…………………………………………………….. 79

Chapter 6 Conclusions 90
6.1 Summary of the present work…………………………….. 90
6.2 Recommendation for future work………………………… 92

References 94

1.Laser Spectroscopy: Basic Concepts and Instrumentation, W. Demtroder, 2nd ed. (Springer-Verlag, Berlin, 1996), Chap. 6.
2.A. G. Bell, “On the production and reproduction of sound by light”, Am. J. Sci. 20, 305 (1880).
3.J. Tyndall, “Action of an intermittent beam of radiant heat upon gaseous matter”, Pro. R. Soc. 31, 307 (1881).
4.W. C. Rontgen, “Upon the Production of sound by radiant energy”, Phil. Mag. J. Sci. 11, 510 (1881).
5.E. L. Kerr, and J. G. Atwood, “The laser illuminated absorptivity spectrophone: a method for measurement of weak absorptivity in gases at laser wavelengths”, Appl. Opt. 7, 915-921 (1968).
6.L. B. Kreuzer, “Ultralow gas concentration infrared absorption spectroscopy”, J. Appl. Phys. 42, 2934-2943 (1971).
7.L. B. Kreuzer, and C. K. N. Patel, “Nitric oxide air pollution: detection by optoacoustic spectroscopy”, Science 173, 45-47 (1971).
8.L. B. Kreuzer, N. D. Kenyon, and C. K. N. Patel, “Air pollution: sensitive detection of ten pollutant gases by carbon monoxide and carbon dioxide lasers”, Science 177, 347-349 (1972).
9.C. K. N. Patel, E. G. Burkhardt, and C. A. Lambert, “Spectroscopic measurements of stratospheric nitric oxide and water vapor”, Science 184, 1173-1176 (1974).
10.E. G. Burkhardt, C. A. Lambert, and C. K. N. Patel, “Stratospheric nitric oxide: measurements during daytime and sunset”, Science 188, 1111-1113 (1975).
11.L. B. Kreuzer, “Laser optoacoustic spectroscopy – a new technique of gas analysis”, Anal. Chem. 46, 239A-244A (1974).
12.L. B. Kreuzer, “Laser optoacoustic spectroscopy for GC detection”, Anal. Chem. 50, 597A-606A (1978).
13.T. Aoki, and M. Katayama, “Impulsive optic-acoustic effect of CO2, SF6 and NH3 molecules”, Japan. J. Appl. Phys. 10, 1303-1310 (1971).
14.J. Wrobel, and M. Vala, “ Time-resolved opto-acoustic spectroscopy”, Chem. Phys. 33, 93-105 (1978).
15.V. N. Bagratashvili, I. N. Knyazev, V. S. Letokhov, and V. V. Lobko, “Optoacoustic detection of multiple photon molecular absorption in a strong IR field”, Opt. Commun. 18, 525-528 (1976).
16.G. A. West, D. R. Siebert, and J. J. Barrett, “Gas phase photoacoustic Raman spectroscopy using pulsed laser excitation”, J. Appl. Phys. 51, 2823-2828 (1980).
17.M. W. Sigrist, S. Bernegger, and P. L. Meyer, “Atmospheric and Exhaust Air Monitoring by Laser Photoacoustic Spectroscopy”, in Photoacoustic, Photothermal and Photochemical Processes in Gases, P. Hess, ed., Vol. 46 of Topics in Current Physics (Springer-Verlag, Berlin, 1989), Chap. 7.
18.F. J. M. Harren, F. G. C. Bijnen, J. Reuss, L. A. C. J. Voesenek, and C. W. P. M. Blom, “Sensitive intracavity photoacoustic measurements with a CO2 waveguide laser”, Appl. Phys. B 50, 137-144 (1990).
19.D. Bicanic, F. Harren, J. Reuss, E. Woltering, J. Snel, L. A. C. J. Voesenek, B. Zuidberg, H. Jalink, F. Bijnen, C. W. P. M. Blom, H. Sauren, M. Kooijman, L. van Hove, and W. Tonk, “Trace Detection in Agriculture and Biology”, in Photoacoustic, Photothermal and Photochemical Processes in Gases, P. Hess, ed., Vol. 46 of Topics in Current Physics (Springer-Verlag, Berlin, 1989), Chap. 8.
20.M. W. Sigrist, “Trace gas monitoring by laser photoacoustic spectroscopy and related techniques”, Rev. Sci. Instrum. 74, 486-490 (2003).
21.M. W. Sigrist, R. Bartlome, D. Marinov, J. M. Rey, D. E. Vogler, and H. Wachter, “Trace gas monitoring with infrared laser-based detection schemes”, Appl. Phys. B 90, 289-300 (2008).
22.S. M. Cristescu, S. T. Persijn, S. te Lintel, Hekkert, and F. J. M. Harren, “Laser-based systems for trace gas detection in life sciences”, Appl. Phys. B 92, 343-349 (2008).
23.M. Nagele, and M. W. Sigrist, “Mobile laser spectrometer with novel resonant multipass photoacoustic cell for trace-gas sensing”, Appl. Phys. B 70, 895-901 (2000).
24.M. W. Sigrist, M. Naegele, D. Lauchenauer, R. Hollmann, and E. Kammer, “Laser photoacoustic analysis of trace gases emitted during electro-knife surgery on human tissue”, Proc. SPIE 4618, 114-120 (2002).
25.J. M. Rey, D. Schramm, D. Hahnloser, D. Marinov, and M. W. Sigrist, “Spectroscopic investigation of volatile compounds produced during thermal and radiofrequency bipolar cautery on porcine liver”, Meas. Sci. Technol. 19, 075602 (2008).
26.M. A. Gondal, “Laser photoacoustic spectrometer for remote monitoring of atmospheric pollutants”, Appl. Opt. 36, 3195-3201 (1997).
27.M. A. Gondal, A. Dastageer, and M. H. Shwehdi, “Photoacoustic spectrometry for trace gas analysis and leak detection using different cell geometries”, Talanta 62, 131-141 (2004).
28.M. A. Gondal, I. A. Bakhtiari, and A. K. Dastageer, “Laser-based sensor for detection of hazardous gases in the air using waveguide CO2 laser”, J. Environ. Sci. Heal. A 42, 871-878 (2007).
29.B. B. Radak, M. T. Petkovska, M. S. Trtica, S. S. Miljanic, and L. T. Petkovska, “Photoacoustic study of CO2-laser coincidences with absorption of some organic solvent vapours”, Anal. Chim. Acta 505, 67-71 (2004).
30.D. S. Maravic, M. S. Trtica, S. S. Miljanic, and B. B. Radak, “Detection of malathion by the CO2 laser: potentials and limitations”, Anal. Chim. Acta 555, 259-262 (2006).
31.Z. Zelinger, M. Strizik, P. Kubat, and S. Civis, “Quantitative analysis of trace mixtures of toluene and xylenes by CO2 laser photoacoustic spectrometry”, Anal. Chim. Acta 422, 179-185 (2000).
32.M. G. da Silva, E. O. Santos, M. S. Sthel, S. L. Cardoso, A. Cavalli, A. R. Monteiro, J. G. de Oliveira, M. G. Pereira, and H. Vargas, “Effect of heat treatment on ethylene and CO2 emissions rates during papaya fruit ripening”, Rev. Sci. Instrum. 74, 703-705 (2003).
33.J. Henningsen, and N. Melander, “Sensitive measurement of adsorption dynamics with nonresonant gas phase photoacoustics”, Appl. Opt. 36, 7037-7045 (1997).
34.M. B. Pushkarsky, M. E. Webber, O. Baghdassarian, L. R. Narasimhan, and C. K. N. Patel, “Laser-based photoacoustic ammonia sensors for industrial applications”, Appl. Phys. B 75, 391-396 (2002).
35.M. B. Pushkarsky, M. E. Webber, and C. K. N. Patel, “Ultra-sensitive ambient ammonia detection using CO2-laser-based photoacoustic spectroscopy”, Appl. Phys. B 77, 381-385 (2003).
36.Photoacoustic Infrared Spectroscopy, K. H. Michaelian, ed. (Wiley Interscience), Chap. 6.
37.L. B. Kreuzer, “The Physics of Signal Generation and Detection”, in Optoacoustic Spectroscopy and Detection, Y. H. Pao (Academic, New York, 1977), Chap. 1.
38.Laser Optoacoustic Spectroscopy, V. P. Zharov, and V. S. Letokhov, ed., Vol. 37 of Springer Ser. Opt. Sci. (Springer-Verlag, Berlin, 1986), Chap. 2.
39.V. Koskinen, J. Fonsen, J. Kauppinen, and I. Kauppinen, “Extremely sensitive trace gas analysis with modern photoacoustic spectroscopy”, Vib. Spectrosc. 42, 239-242 (2006).
40.C. F. Dewey Jr., and R. D. Kamm, C. E. Hackett, “Acoustic amplifier for detection of atmospheric pollutants”, Appl. Phys. Lett. 23, 633-635 (1973).
41.Laser Optoacoustic Spectroscopy, V. P. Zharov, and V. S. Letokhov, ed., Vol. 37 of Springer Ser. Opt. Sci. (Springer-Verlag, Berlin, 1986), Chap. 5.
42.C. F. Dewey Jr., “Design of Optoacoustic Systems”, in Optoacoustic Spectroscopy and Detection, Y. H. Pao (Academic, New York, 1977), Chap. 3.
43.Laser Engineering, K. J. Kuhn, ed. (Prentice Hall, Upper Saddle River, 1998), Chap. 12.
44.P. Vidaud, D. He, and D. R. Hall, “High efficiency RF excited CO2 laser”, Opt. Commun. 56, 185-190 (1985).
45.S. Y. Shaw, and R. S. Chang, “Wide-range line tunable CO2 waveguide lasers with segmented ratio frequency exitation”, Proc. Natl. Sci. Counc. ROC(A) 21, 623-629 (1997).
46.S. Y. Shaw, and R. S. Chang, “Radio frequency excited waveguide CO2 lasers on sequence-band transitions”, Appl. Phys. B 67, 39-45 (1998).
47.A. M. Holohan, and S. L. Prunty, “Line selection in carbon dioxide waveguide lasers using diffraction gratings”, Infrared Phys. 23, 149-156 (1983).
48.V. N. Bel’tyugov, A. A. Kuznetsov, V. N. Ochkin, N. N. Sobolev, Yu. V. Troitskii, and Yu. B. Udalov, “Frequency selectivity and resonator losses in a waveguide laser with a diffraction grating”, Sov. J. Quantum Electron. 16, 881-887 (1986).
49.AOAC (American Organization of Analytical Chemists), 1990. Wines. In Official methods of analysis of AOAC international, 15th Edition, pp. 739-750.
50.S. A. Savchuk, V. N. Vlasov, S. A. Appolonova, V. N. Arbuzov, A. N. Vedenin, A. B. Mezinov, and B. R. Grigor’yan, “Application of Chromatography and Spectrometry to the Authentication of Alcoholic Beverages,” J. Analyt. Chem. 56, 214-231(2001).
51.R. A. Peinado, J. A. Moreno, D. Munoz, M. Medina, and J. Moreno, “Gas Chromatographic Quantification of Major Volatile Compounds and Polyols in Wine by Direct Injection,” J. Agric. Food Chem. 52, 6389-6393 (2004).
52.T. Cabaroglu, “Methanol contents of Turkish varietal wines and effect of processing,” Food Contr. 16, 177-181 (2005).
53.G. Busse, and K. F. Renk, “Use of the opto-acoustic effect for far-infrared gas lasers,” Infrared Phys. 18, 517-519 (1978).
54.M. Inguscio, N. Ioli, A. Moretti, F. Strumia, and F. D’Amato, “Atlas of CH3OH absorption spectroscopy by using a 395 MHz tunable CO2 waveguide laser,” Int. J. infrared mm waves 5, 1615-1639 (1984).
55.G. Merkle, and J. Heppner, “IR absorption measurements and new FIR emission lines in CH3OH by use of a frequency-tunable CW waveguide CO2 laser,” Opt. Comm. 51, 265-270 (1984).
56.E. K. Plyler, “Infrared Spectra of Methanol, Ethanol, and n-Propanol,” J. Research NBS 48, 281-286 (1952).
57.G. Schafer, H. Hofmann, and W. D. Petersen, “Tunable CO2 waveguide laser with high transverse mode and line discrimination”, IEEE J. Quantum Electron. QE-18, 87-90 (1982).
58.F. Tang, and J. O. Henningsen, “A 500 MHz tunable CO2 waveguide laser for optical pumping”, IEEE J. Quantum Electron. QE-22, 2084-2087 (1986).
59.F. Tang, and J. O. Henningsen, “Conditions for Single-Line and Single-Mode Tuning of a CO2 Waveguide Laser,” Appl. Phys. B 44, 93-98 (1987).
60.M. S. Shumate, R. T. Menzies, J. S. Margolis, and L. -G. Rosengren, “Water vapor absorption of carbon dioxide laser radiation,” Appl. Opt. 15, 2480-2488 (1976).
61.J. C. Peterson, M. E. Thomas, R. J. Nordstrom, E. K. Damon, and R. K. Long, “Water vapor-nitrogen absorption at CO2 laser frequencies,” Appl. Opt. 18, 834-841 (1979).
62.G. L. Loper, M. A. O’Neill, and J. A. Gelbwachs, “Water-vapor continuum CO2 laser absorption spectra between 27°C and -10°C,” Appl. Opt. 22, 3701-3710 (1983).
63.ASTM (American Society for Testing and Materials) D 4815, Standard Test Method for Determination of MTBE, ETBE, TAME, DIPE, tertiary-Amyl Alcohol and C1 to C4 Alcohol in Gasoline by Gas Chromatography, 1999.
64.ASTM D 5599, Standard Test Method for Determination of Oxygenates in Gasoline by Gas Chromatography and Oxygen Selective Flame Ionization Detection, 2000.
65.S. L. Tackett, “Determination of methanol in gasoline by gas chromatography”, Analyst 112, 339-340 (1987).
66.B. R. Buchanan, and D. E. Honigs, “Detection of methanol in gasolines using near-infrared spectroscopy and an optical fiber”, Appl. Spectrosc. 41, 1388-1392 (1987).
67.A. Lob, R. Buenafe, and N. M. Abbas, “Determination of oxygenates in gasoline by FTIR”, Fuel 77, 1861-1864 (1998).
68.H. L. Fernandes, I. M. Raimundo Jr, C. Pasquini, and J. J. R. Rohwedder, “Simultaneous determination of methanol and ethanol in gasoline using NIR spectroscopy: Effect of gasoline composition”, Talanta 75, 804-810 (2008).
69.E. Lopez-Anreus, S. Garrigues, and M. de la Guardia, “Vapour generation-Fourier transform infrared spectrometric determination of benzene, toluene and methyl tert.-butyl ether in gasolines”, Anal. Chim. Acta 333, 157-165 (1996).
70.J. A. Pumphrey, J. I. Brand, and W. A. Scheller, “Vapour pressure measurements and predictions for alcohol-gasoline blends”, Fuel 79, 1405-1411 (2000).
71.F. Bianchi, M. Careri, E. Marengo, and M. Musci, “Use of experimental design for the purge-and-trap-gas chromatography-mass spectrometry determination of methyl tert.-butyl ether, tert.-butyl alcohol and BTEX in groundwater at trace level”, J. Chromatogr. A 975, 113-121 (2002).
72.M. Rosell, S. Lacorte, A. Ginebreda, and D. Barcelo, “Simultaneous determination of methyl tert.-butyl ether and its degradation products, other gasoline oxygenates and benzene, toluene, ethylbenzene and xylenes in Catalonian groundwater by purge-and-trap-gas chromatography-mass spectrometry”, J. Chromatogr. A 995, 171-184 (2003).
73.J. L. P. Pavon, M. del N. Sanchez, M. E. F. Laespada, and B. M. Cordero, “Simultaneous determination of gasoline oxygenates and benzene, toluene, ethylbenzene and xylene in water samples using headspace-programmed temperature vaporization-fast gas chromatography-mass spectrometry”, J. Chromatogr. A 1175, 106-111 (2007).
74.C. P. Rinsland, V. M. Devi, T. A. Blake, R. L. Sams, S. Sharpe, and L. Chiou, “Quantitative measurement of integrated band intensities of benzene vapor in the mid-infrared at 278, 298 and 323 K”, J. Quant. Spectrosc. Radiat. Transfer 109, 2511-2522 (2008).
75.P. M. Chu, F. R. Guenther, G. C. Rhoderick, and W. J. Lafferty, “The NIST quantitative infrared database”, J. Res. Natl. Inst. Stand. Technol. 104, 59-81 (1999).
76.Alcohol Breath Tester, http://www.cpu.com.tw/kh/home/alcohol/abt280.html.
77.http://www.laboratoryequipment.com/article-taking-alcohol-abuse-off-road-ct92.aspx
78.B. S. De Martinis, M. A. M. Ruzzene, and C. C. S. Martin, “Determination of ethanol in human blood and urine by automated headspace solid-phase microextraction and capillary gas chromatography”, Anal. Chim. Acta 522, 163-168 (2004).
79.D. A. Labianca, “Breath-alcohol analysis: a commentary on ethanol specificity in the 3-μm and 9-μm regions of the IR spectrum”, Forensic Toxicol 24, 92-94 (2006).
80.M. Hammerich, A. Olafsson, and J. Henningsen, “Photoacoustic study of kinetic cooling”, Chem. Phys. 163, 173-178 (1992).
81.http://webbook.nist.gov/chemistry/form-ser.html.en-us.en (NIST, USA).