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Nitrogen-laser-pumped resonator-amplifier tunable dye laser system for fluorescence decay lifetime measurements
Optik 125 (2014) 4726–4728
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Nitrogen-laser-pumped resonator-amplifier tunable dye laser system for fluorescence decay lifetime measurements Sami D. Alaruri Independent Scholar, P.O. Box 152, Uniontown, OH 44685, USA
a r t i c l e
i n f o
Article history: Received 11 September 2013 Accepted 24 April 2014 Keywords: Dye laser Nitrogen laser Laser amplifier Echelle grating Fluorescence decay lifetime
a b s t r a c t In this work, a description for an experimental nitrogen-laser-pumped resonator-amplifier tunable dye laser which is part of a measurement system constructed for exciting and collecting fluorescence decay lifetime measurements from fresh and naturally weathered oil samples is given. The results of fluorescence lifetime measurements collected from fresh and crude oils using 428 nm excitation are reported. Furthermore, a brief description for a simple deconvolution procedure which employs fast Fourier transforms for determining the average lifetime of oils is provided. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Fluorescence decay lifetimes collected using laser fluorescensing techniques from crude and refined oils have been considered as a characterization parameter for oil spills detection and identification in a marine environment by many researchers [1–14]. Other parameters such as fluorescence spectra [1,5,10–13] and conversion efficiency [1,7,8] were employed as well in the identification and characterization of oil spills. The present paper describes the construction and characterization of an experimental N2 laser-pumped resonator-amplifier dye laser [15–28] which is part of a system used for collecting fluorescence decay lifetime measurements from crude and refined oils [1–6]. The dye laser system is compact, easy to construct, rugged and inexpensive. In addition, the paper describes a simple deconvolution technique which employs fast Fourier transforms for calculating the oil sample decay lifetime. Lastly, the paper provides examples for fresh and naturally weathered oils fluorescence decay lifetime measurements collected over the spectral range 460–720 nm. 2. Measurement system description The N2 laser-pumped tunable dye laser system is schematically shown in Fig. 1. The emitted nitrogen laser 337.1 nm (5 mJ/pulse,
E-mail address: sami [email protected] http://dx.doi.org/10.1016/j.ijleo.2014.04.082 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
pulse FWHM ∼ 1.0 ns, 10 Hz) laser beam was split into two portions using a 50%:50% dichroic beam splitter and the two beams were used to pump both the resonator and amplifier stages of the tunable dye laser system. A neutral density filter was inserted in front of the resonator stage to prevent saturation. The splitted N2 laser beams were focused into the dye laser resonator-amplifier quartz cuvettes (length = 1 cm) filled with Stilbene 420 dye by the means of two cylindrical lenses (FL = 10 cm, quartz). The four sides of the quartz cuvettes were optically polished and the N2 laser beams were focused to approximately 0.15 mm thick line inside the two cuvettes. The resonator and amplifier cuvettes were tilted by approximately 2◦ to prevent back reflections and the generation of spontaneous emission. The dye laser resonator cavity stage was of Hänsch design [15] and the cavity length was approximately 5 cm. The dye laser resonator cavity incorporates an output coupler (approximately 20% reflectivity) and an Echelle grating (100% reflector; 79 grooves/mm with blaze angle of 63.4◦ ) which was mounted on an X–Y–Z and rotating stages. The coarsely ruled Echelle diffraction grating was used in tuning the dye laser system emission wavelength to 428 nm. The dye laser system generates 3–4 ns FWHM pulses which were required for determining the intrinsic fluorescence decay lifetimes of fresh and weather oils. The 428 nm beam emerging from the dye laser beam system was directed toward the oil sample by the means of a dichroic beam splitter (∼80%:∼20%). Also, the beam splitter allows the transmission of the oil sample fluorescence radiation from 460 nm to 720 nm. As shown in Fig. 1, a portion of the 428 nm laser beam transmitted through the beam splitter was focused into a photodiode. The photodiode output was used for monitoring the temporal
Pulse Amplitude (Arbitrary Units)
S.D. Alaruri / Optik 125 (2014) 4726–4728
4727
80 70 60 50 40 30 20 10 0 0
2
4
6
Laser Pulse
8
10
12 14 Time (ns)
16
18
Pulse Obtained By Deconvoluon
20
22
24
Fluorescence Pulse
profiles of the generated 428 nm dye laser pulses and for triggering the oscilloscope. Fluorescence radiation generated from a 1000 m oil sample formed on top of a filtered sea water column and contained in a 2-L glass cylinder was transmitted through a beam splitter placed in top of the oil sample and focused into a fiber-optic bundle (0.5 m long) [29] by the means of a short focal length quartz lens. The outputend of fiber optic bundle was coupled into the entrance slit of a computer-controlled monochromator. A cut-off optical filter was placed inside the monochromator and behind the monachromator entrance slit to block the 428 nm scattered radiation from reaching the photomultiplier tube (Hamamatsu-R955). The photomultiplier tube output was fed into a specially designed circuit for short pulse detection (risetime approximately 1.0 ns). Radiation emerging from the monochromator exit slit was coupled to the photomultiplier tube via a quartz rod (∼6.0 mm in diameter). The bandwidth of the monochromator was set to 8 nm. Data were collected by sequentially scanning the stepper motor of the monochromator in 20 nm steps over the spectral range 460–720 nm. 3. Results and discussion Prior to collecting fluorescence lifetime measurements from oils the measurement system performance was validated by measuring the decay lifetimes of three laser dyes, namely, stilbene 420, courmarine 481 and oxazine 720. As shown in Table 1, the three dyes were prepared in ethanol to a 5 × 10−3 M molar concentration. The measured fluorescence lifetimes using the N2 laser-pumped dye laser system for stilbene 420, coumarine 481 and oxazine 720 were 0.92 ± 0.06 ns, 0.60 ± 0.04 ns and 4.20 ± 0.29 ns, respectively. These decay lifetime measurements were in good agreement with similar measurements reported by Quinn et al. [30] and Liu [31]. Average fluorescence lifetimes for fresh and weathered oils were calculated by performing a deconvolution procedure which employs fast Fourier transforms. As depicted in Fig. 2, the procedure deconvolves the measured oil fluorescence pulses from the 428 nm dye laser pulse and from the system impulse response and then calculates the average oil fluorescence decay lifetime. Assuming a linear behavior for the fluorescence measured signal and for the
Table 1 List of fluorescence decay lifetime measured for stilbene 420, coumarine 481 and oxazine 720 dye solutions using the N2 laser-pumped dye laser system to validate the system performance. The total measurement errors were estimated at ±7%. Dye name Stilbene 420 Coumarine 481 Oxazine 720
Solvent/molar concentration (M)
Measured fluorescence decay lifetime (ns)
Ethanol/5 × 10−3 Ethanol/5 × 10−3 Ethanol/5 × 10−3
0.92 ± 0.06 0.60 ± 0.04 4.20 ± 0.29
5 4.5 4 3.5 3 2.5 2 1.5
LHF04 LCR13 LCR12 LMD02
1
LCR22
0.5 0 460
510
560
610 Wavelength (nm)
660
710
Fig. 3. Graph showing fluorescence lifetimes plotted as a function of wavelength for LHF04 = straight fuel, LCR13 = Wafra-Burgan stream-crude oil, LCR12 = Kuwaiti export-crude oil, LMD02 = marine diesel oil, and LCR22 = offshore limestone-crude oil. All oil samples were fresh and 1000 m thick [1].
electro-optical measurement system, the measured fluorescence decay curve f(t) can be described by the convolution integral: f (t) = l(t) × h(t) × g(t)
(1)
where l(t) is the dye laser pulse, h(t) is the impulse response of the oil sample and g(t) is the impulse response of the apparatus. A detailed description for the employed deconvolution technique is provided in Ref. [2]. Examples for fluorescence lifetime measurements collected from 1000 m thick fresh samples of straight fuel, diesel oil and three different types of crude oils as a function of wavelength are shown in Fig. 3. As shown in Fig. 3, the smallest decay lifetime measurements (0.25–1.7 ns) were recorded for the marine diesel oil (LMD02) sample and the largest lifetime measurements (1.8–4.8 ns) were recorded for the offshore limestone crude oil (LCR22) sample. An observation to be made is that the fluorescence lifetimes for refined and crude oils increased in value with wavelength in almost a linear manner. Fig. 4 shows a typical set of fluorescence lifetime measurements obtained from LCR02 offshore crude oil film (1000 m thick) exposed to 2 h, 5 h, 10 h, 5 days and 10 days of natural weathering. Here, it is worth noting that for the majority of investigated refined and crude oil sample a decrease in fluorescence lifetimes was observed during the first 10 h of weathering and the decay lifetimes remained constant with further weathering to the oil films.
Fluorescence Lifemes (ns)
Fig. 1. Block diagram showing the N2 laser-pumped resonator-amplifier tunable dye laser which is part of a system constructed for collecting fluorescence decay lifetime measurements from fresh and naturally weathered oil samples.
Fluorescence Lifemes (ns)
Fig. 2. Plot showing a typical 428 nm dye laser pulse, a measured oil fluorescence pulse and a decay lifetime pulse calculated using the deconvolution technique [2].
2.5 2 2 Hours
1.5
5 Hours 1
10 Hours 5 days
0.5
10 Days
0 460
500
540
580
620
660
700
740
Wavelength (nm)
Fig. 4. Graph illustrating fluorescence lifetimes measured for a naturally weathered 1000 m thick LCR02 = Offshore-crude oil sample. The sample was weathered for 2 h, 5 h, 10 h, 5 days and 10 days [1].
4728
S.D. Alaruri / Optik 125 (2014) 4726–4728
The oil films weathering was carried out in a static weathering rig and atmospheric parameters such as global solar radiation, diffused solar radiation, UV radiation, IR radiation, ambient temperature, relative humidity, wind speed, etc. [32–36] were continuously monitored using an automated weather station [37]. 4. Conclusions A pulsed N2 laser-pumped resonator-amplifier tunable dye laser was constructed and validate using stilbene 420, coumarine 481 and oxazine 720 dye solutions. The dye laser is part of a fluorescence decay lifetime measurement system which is used for collecting data from fresh and naturally weathered crude and refine oils. Based on the obtained results the following two conclusions can be drawn: (1) For fresh and weathered oils fluorescence lifetime values increased in value over the 460–720 nm spectral range in almost a linear manner. (2) For the majority of crude and refined weathered oils fluorescence lifetime values decreased within the first 10 h and remained constant thereafter. References [1] S.D. Alaruri, M. Rasas, O. Alamedine, S. Jubian, F. Al-Bahrani, M.F. Quinn, Remote characterization of crude and refined oils using a laser fluorosensor system, Opt. Eng. 34 (January (1)) (1995) 214–221. [2] M.F. Quinn, S. Joubian, F. Al-Bahrani, S. Al-Aruri (Alaruri), O. Alameddine, A deconvolution technique for determining the intrinsic fluorescence decay lifetimes of crude oils, Appl. Spectrosc. 42 (3) (1988) 406–410. [3] A.G. Ryder, T.J. Glynn, M. Feely, A.J.G. Barwise, Characterization of crude oils using fluorescence lifetime data, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 58 (March (5)) (2002) 1025–1037. [4] R.M. Measures, H.R. Houston, D.G. Stephenson, Laser induced fluorescent decay spectra, a new form of environmental signature, Opt. Eng. 13 (1974) 494–501. [5] P. Carnagni, A. Colornbo, C. Koecher, N. Ornenetto, P. Qi, G. Rossi, Fluorescence response of mineral oils: spectral yields vs. absorption and decay time, Appl. Opt. 30 (1991) 26–35. [6] D.M. Rayner, A.G. Szabo, Time-resolved laser fluorosensor: a laboratory study of their potential in the remote characterization of oil, Appl. Opt. 17 (1978) 1624–1630. [7] F.E. Hoge, R.N. Swift, Experimental feasibility of the airborne measurement of absolute oil fluorescence spectral conversion efficiency, Appl. Opt. 22 (1983) 37–47. [8] R.T.V. Kung, I. Itzkan, Absolute oil fluorescence conversion efficiency, Appl. Opt. 15 (1976) 409–415. [9] T. Fujii, T. Fukuchi, Laser Remote Sensing, CRC Press, Boca Raton, FL, 2005. [10] R. Karpicz, A. Dementjev, Z. Kuprionis, S. Pakalnis, R. Westphal, R. Reuter, V. Gulbinas, Oil spill fluorosensing LIDAR for inclined onshore or shipboard operation, Appl. Opt. 45 (25) (2006) 6620–6625.
[11] M.N. Jha, Development of Laser Fluorosensor Data Processing System and GIS Tools for Oil Spill Response (M.S. Thesis), University of Calgary, 2009. [12] S. Svanberg, Environmental monitoring using optical techniques, Appl. Laser Spectrosc. 241 (1990) 417–434. [13] S. Svanberg, S. Montan, Fluorescence Imaging System, US Patent US4786813 (1988). [14] E.C. Brown, M.F. Fingas, Review of the development of laser fluorosensors for oil spill applications, Mar. Pollut. Bull. 47 (December (9–12)) (2003) 477–484. [15] T.W. Hänsch, Repetitively pulsed tunable dye laser for high resolution spectroscopy, Appl. Opt. 11 (April (4)) (1972) 895–898. [16] F.P. Schäfer, Dye Lasers, Volume 1 of Topics in Applied Physics, 3rd ed., SpringerVerlag, New York, 1990. [17] R.C. Hilborn, Design and construction of simple, nitrogen-laser-pumped, tunable dye laser, Am. J. Phys. 46 (May (5)) (1978) 565–572. [18] J. Sohnl, S.G. Payton, A modular, reconfigurable-cavity, pulsed dye laser for the advanced undergraduate laboratory, Am. J. Phys. 65 (July (7)) (1997) 640–652. [19] J.E. Lawler, W.A. Fitzsimmons, L.W. Anderson, Narrow bandwidth dye laser suitable for pumping by a short pulse duration N2 laser, Appl. Opt. 15 (April (4)) (1976) 1083–1090. [20] C.V. Shank, Physics of dye lasers, Rev. Mod. Phys. 47 (July (3)) (1975) 649–657. [21] I.S. Gordon, A Nitrogen-Laser-Pumped Dye Laser System (M.S. Thesis), Simon Fraser University, Canada, 1972. [22] S. Saikan, Nitrogen-laser-pumped single-mode dye laser, Appl. Phys. 17 (1978) 41–44. [23] F.J. Duarte, Organic dye lasers, Opt. Photonics News (2003) 20–25. [24] G. Capelle, D. Phillips, Tuned nitrogen laser pumped dye laser, Appl. Opt. 9 (December (12)) (1970) 2742–2745. [25] A. Zhiglinsky, A.M. Izmailov, Multi-Wavelength Tunable Laser, US Patent 5,428,635 (1995). [26] G. Cook, Dye Laser Amplifiers, US Patent 5,379,147 (1995). [27] J. Myer, R.D. Sharma, E.J. Kierstead, Transverse Dye Laser Stimulation with a Pulsed Nitrogen Laser, US Patent 3,684,979 (1972). [28] Itzkan et al., Narrow Bandwidth Dye Laser, US Patent 3,868,590 (1975). [29] S. Alaruri, A. Brewington, G. Bijak, Measurement of modal dispersion for a stepindex multimode optical fiber in the UV–visible region using a pulsed laser, Appl. Spectrosc. 48 (2) (1994) 228–231. [30] M.F. Quinn, M.S. Al-Ajeel, F. Al-Bahrani, Measurements of nanosecond lifetimes using a transient method based on pulse delay, J. Lumin. 33 (1985) 53–61. [31] L.-I. Liu, Time-Resolved Fluorescence Studies of Dye-Polymers as Excited by Laser and Beta-Radiation (M.S. Thesis), Texas Tech University, 1997. [32] S. Al-Aruri (Alaruri), M. Rasas, K. Al-Jamal, N. Shaban, An assessment of global ultraviolet solar radiation in the range (0.290–0.385 m) in Kuwait, Sol. Energy 41 (2) (1988) 159–162. [33] K. Al-Jamal, S. Ayyash, M. Rasas, S. Al-Aruri (Alaruri), N. Shaban, Atmospheric turbidity in Kuwait, Atmos. Environ. 21 (8) (1987) 1855–1859. [34] S.D. Alaruri, M.F. Amer, Empirical regression models for weather data measured in Kuwait during the years 1985, 1986, and 1987, Sol. Energy 50 (3) (1993) 229–233. [35] S. Al-Aruri (Alaruri), The empirical relationship between global and global ultraviolet (290–385) nm solar radiation components, Sol. Energy 45 (2) (1990) 61–64. [36] K. Al-Jamal, N. Shaban, M. Rasas, M. Quinn, S. Al-Aruri (Alaruri), J. D’Souza, Investigation of solar radiation in Kuwait, in: Proceedings of the Second International Solar Energy Conference, Bahrain, 15–24 February, 1986. [37] S. Al-Aruri (Alaruri), A. Al-Otaibi, H. Darwish, N. Al-Awadi, M.F. Quinn, J. D’Souza, Development of a PC compatible automatic weather station, J. Meteorol. 13 (131) (1988) 227–281.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Nitrogen-laser-pumped resonator-amplifier tunable dye laser system for fluorescence decay lifetime measurements Sami D. Alaruri Independent Scholar, P.O. Box 152, Uniontown, OH 44685, USA
a r t i c l e
i n f o
Article history: Received 11 September 2013 Accepted 24 April 2014 Keywords: Dye laser Nitrogen laser Laser amplifier Echelle grating Fluorescence decay lifetime
a b s t r a c t In this work, a description for an experimental nitrogen-laser-pumped resonator-amplifier tunable dye laser which is part of a measurement system constructed for exciting and collecting fluorescence decay lifetime measurements from fresh and naturally weathered oil samples is given. The results of fluorescence lifetime measurements collected from fresh and crude oils using 428 nm excitation are reported. Furthermore, a brief description for a simple deconvolution procedure which employs fast Fourier transforms for determining the average lifetime of oils is provided. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Fluorescence decay lifetimes collected using laser fluorescensing techniques from crude and refined oils have been considered as a characterization parameter for oil spills detection and identification in a marine environment by many researchers [1–14]. Other parameters such as fluorescence spectra [1,5,10–13] and conversion efficiency [1,7,8] were employed as well in the identification and characterization of oil spills. The present paper describes the construction and characterization of an experimental N2 laser-pumped resonator-amplifier dye laser [15–28] which is part of a system used for collecting fluorescence decay lifetime measurements from crude and refined oils [1–6]. The dye laser system is compact, easy to construct, rugged and inexpensive. In addition, the paper describes a simple deconvolution technique which employs fast Fourier transforms for calculating the oil sample decay lifetime. Lastly, the paper provides examples for fresh and naturally weathered oils fluorescence decay lifetime measurements collected over the spectral range 460–720 nm. 2. Measurement system description The N2 laser-pumped tunable dye laser system is schematically shown in Fig. 1. The emitted nitrogen laser 337.1 nm (5 mJ/pulse,
E-mail address: sami [email protected] http://dx.doi.org/10.1016/j.ijleo.2014.04.082 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
pulse FWHM ∼ 1.0 ns, 10 Hz) laser beam was split into two portions using a 50%:50% dichroic beam splitter and the two beams were used to pump both the resonator and amplifier stages of the tunable dye laser system. A neutral density filter was inserted in front of the resonator stage to prevent saturation. The splitted N2 laser beams were focused into the dye laser resonator-amplifier quartz cuvettes (length = 1 cm) filled with Stilbene 420 dye by the means of two cylindrical lenses (FL = 10 cm, quartz). The four sides of the quartz cuvettes were optically polished and the N2 laser beams were focused to approximately 0.15 mm thick line inside the two cuvettes. The resonator and amplifier cuvettes were tilted by approximately 2◦ to prevent back reflections and the generation of spontaneous emission. The dye laser resonator cavity stage was of Hänsch design [15] and the cavity length was approximately 5 cm. The dye laser resonator cavity incorporates an output coupler (approximately 20% reflectivity) and an Echelle grating (100% reflector; 79 grooves/mm with blaze angle of 63.4◦ ) which was mounted on an X–Y–Z and rotating stages. The coarsely ruled Echelle diffraction grating was used in tuning the dye laser system emission wavelength to 428 nm. The dye laser system generates 3–4 ns FWHM pulses which were required for determining the intrinsic fluorescence decay lifetimes of fresh and weather oils. The 428 nm beam emerging from the dye laser beam system was directed toward the oil sample by the means of a dichroic beam splitter (∼80%:∼20%). Also, the beam splitter allows the transmission of the oil sample fluorescence radiation from 460 nm to 720 nm. As shown in Fig. 1, a portion of the 428 nm laser beam transmitted through the beam splitter was focused into a photodiode. The photodiode output was used for monitoring the temporal
Pulse Amplitude (Arbitrary Units)
S.D. Alaruri / Optik 125 (2014) 4726–4728
4727
80 70 60 50 40 30 20 10 0 0
2
4
6
Laser Pulse
8
10
12 14 Time (ns)
16
18
Pulse Obtained By Deconvoluon
20
22
24
Fluorescence Pulse
profiles of the generated 428 nm dye laser pulses and for triggering the oscilloscope. Fluorescence radiation generated from a 1000 m oil sample formed on top of a filtered sea water column and contained in a 2-L glass cylinder was transmitted through a beam splitter placed in top of the oil sample and focused into a fiber-optic bundle (0.5 m long) [29] by the means of a short focal length quartz lens. The outputend of fiber optic bundle was coupled into the entrance slit of a computer-controlled monochromator. A cut-off optical filter was placed inside the monochromator and behind the monachromator entrance slit to block the 428 nm scattered radiation from reaching the photomultiplier tube (Hamamatsu-R955). The photomultiplier tube output was fed into a specially designed circuit for short pulse detection (risetime approximately 1.0 ns). Radiation emerging from the monochromator exit slit was coupled to the photomultiplier tube via a quartz rod (∼6.0 mm in diameter). The bandwidth of the monochromator was set to 8 nm. Data were collected by sequentially scanning the stepper motor of the monochromator in 20 nm steps over the spectral range 460–720 nm. 3. Results and discussion Prior to collecting fluorescence lifetime measurements from oils the measurement system performance was validated by measuring the decay lifetimes of three laser dyes, namely, stilbene 420, courmarine 481 and oxazine 720. As shown in Table 1, the three dyes were prepared in ethanol to a 5 × 10−3 M molar concentration. The measured fluorescence lifetimes using the N2 laser-pumped dye laser system for stilbene 420, coumarine 481 and oxazine 720 were 0.92 ± 0.06 ns, 0.60 ± 0.04 ns and 4.20 ± 0.29 ns, respectively. These decay lifetime measurements were in good agreement with similar measurements reported by Quinn et al. [30] and Liu [31]. Average fluorescence lifetimes for fresh and weathered oils were calculated by performing a deconvolution procedure which employs fast Fourier transforms. As depicted in Fig. 2, the procedure deconvolves the measured oil fluorescence pulses from the 428 nm dye laser pulse and from the system impulse response and then calculates the average oil fluorescence decay lifetime. Assuming a linear behavior for the fluorescence measured signal and for the
Table 1 List of fluorescence decay lifetime measured for stilbene 420, coumarine 481 and oxazine 720 dye solutions using the N2 laser-pumped dye laser system to validate the system performance. The total measurement errors were estimated at ±7%. Dye name Stilbene 420 Coumarine 481 Oxazine 720
Solvent/molar concentration (M)
Measured fluorescence decay lifetime (ns)
Ethanol/5 × 10−3 Ethanol/5 × 10−3 Ethanol/5 × 10−3
0.92 ± 0.06 0.60 ± 0.04 4.20 ± 0.29
5 4.5 4 3.5 3 2.5 2 1.5
LHF04 LCR13 LCR12 LMD02
1
LCR22
0.5 0 460
510
560
610 Wavelength (nm)
660
710
Fig. 3. Graph showing fluorescence lifetimes plotted as a function of wavelength for LHF04 = straight fuel, LCR13 = Wafra-Burgan stream-crude oil, LCR12 = Kuwaiti export-crude oil, LMD02 = marine diesel oil, and LCR22 = offshore limestone-crude oil. All oil samples were fresh and 1000 m thick [1].
electro-optical measurement system, the measured fluorescence decay curve f(t) can be described by the convolution integral: f (t) = l(t) × h(t) × g(t)
(1)
where l(t) is the dye laser pulse, h(t) is the impulse response of the oil sample and g(t) is the impulse response of the apparatus. A detailed description for the employed deconvolution technique is provided in Ref. [2]. Examples for fluorescence lifetime measurements collected from 1000 m thick fresh samples of straight fuel, diesel oil and three different types of crude oils as a function of wavelength are shown in Fig. 3. As shown in Fig. 3, the smallest decay lifetime measurements (0.25–1.7 ns) were recorded for the marine diesel oil (LMD02) sample and the largest lifetime measurements (1.8–4.8 ns) were recorded for the offshore limestone crude oil (LCR22) sample. An observation to be made is that the fluorescence lifetimes for refined and crude oils increased in value with wavelength in almost a linear manner. Fig. 4 shows a typical set of fluorescence lifetime measurements obtained from LCR02 offshore crude oil film (1000 m thick) exposed to 2 h, 5 h, 10 h, 5 days and 10 days of natural weathering. Here, it is worth noting that for the majority of investigated refined and crude oil sample a decrease in fluorescence lifetimes was observed during the first 10 h of weathering and the decay lifetimes remained constant with further weathering to the oil films.
Fluorescence Lifemes (ns)
Fig. 1. Block diagram showing the N2 laser-pumped resonator-amplifier tunable dye laser which is part of a system constructed for collecting fluorescence decay lifetime measurements from fresh and naturally weathered oil samples.
Fluorescence Lifemes (ns)
Fig. 2. Plot showing a typical 428 nm dye laser pulse, a measured oil fluorescence pulse and a decay lifetime pulse calculated using the deconvolution technique [2].
2.5 2 2 Hours
1.5
5 Hours 1
10 Hours 5 days
0.5
10 Days
0 460
500
540
580
620
660
700
740
Wavelength (nm)
Fig. 4. Graph illustrating fluorescence lifetimes measured for a naturally weathered 1000 m thick LCR02 = Offshore-crude oil sample. The sample was weathered for 2 h, 5 h, 10 h, 5 days and 10 days [1].
4728
S.D. Alaruri / Optik 125 (2014) 4726–4728
The oil films weathering was carried out in a static weathering rig and atmospheric parameters such as global solar radiation, diffused solar radiation, UV radiation, IR radiation, ambient temperature, relative humidity, wind speed, etc. [32–36] were continuously monitored using an automated weather station [37]. 4. Conclusions A pulsed N2 laser-pumped resonator-amplifier tunable dye laser was constructed and validate using stilbene 420, coumarine 481 and oxazine 720 dye solutions. The dye laser is part of a fluorescence decay lifetime measurement system which is used for collecting data from fresh and naturally weathered crude and refine oils. Based on the obtained results the following two conclusions can be drawn: (1) For fresh and weathered oils fluorescence lifetime values increased in value over the 460–720 nm spectral range in almost a linear manner. (2) For the majority of crude and refined weathered oils fluorescence lifetime values decreased within the first 10 h and remained constant thereafter. References [1] S.D. Alaruri, M. Rasas, O. Alamedine, S. Jubian, F. Al-Bahrani, M.F. Quinn, Remote characterization of crude and refined oils using a laser fluorosensor system, Opt. Eng. 34 (January (1)) (1995) 214–221. [2] M.F. Quinn, S. Joubian, F. Al-Bahrani, S. Al-Aruri (Alaruri), O. Alameddine, A deconvolution technique for determining the intrinsic fluorescence decay lifetimes of crude oils, Appl. Spectrosc. 42 (3) (1988) 406–410. [3] A.G. Ryder, T.J. Glynn, M. Feely, A.J.G. Barwise, Characterization of crude oils using fluorescence lifetime data, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 58 (March (5)) (2002) 1025–1037. [4] R.M. Measures, H.R. Houston, D.G. Stephenson, Laser induced fluorescent decay spectra, a new form of environmental signature, Opt. Eng. 13 (1974) 494–501. [5] P. Carnagni, A. Colornbo, C. Koecher, N. Ornenetto, P. Qi, G. Rossi, Fluorescence response of mineral oils: spectral yields vs. absorption and decay time, Appl. Opt. 30 (1991) 26–35. [6] D.M. Rayner, A.G. Szabo, Time-resolved laser fluorosensor: a laboratory study of their potential in the remote characterization of oil, Appl. Opt. 17 (1978) 1624–1630. [7] F.E. Hoge, R.N. Swift, Experimental feasibility of the airborne measurement of absolute oil fluorescence spectral conversion efficiency, Appl. Opt. 22 (1983) 37–47. [8] R.T.V. Kung, I. Itzkan, Absolute oil fluorescence conversion efficiency, Appl. Opt. 15 (1976) 409–415. [9] T. Fujii, T. Fukuchi, Laser Remote Sensing, CRC Press, Boca Raton, FL, 2005. [10] R. Karpicz, A. Dementjev, Z. Kuprionis, S. Pakalnis, R. Westphal, R. Reuter, V. Gulbinas, Oil spill fluorosensing LIDAR for inclined onshore or shipboard operation, Appl. Opt. 45 (25) (2006) 6620–6625.
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