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Measurement of H2O concentration by tunalbe laser absorption spectroscopy technique with a Tm:YAP solid-state laser
Optik 127 (2016) 8277–8280
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Measurement of H2 O concentration by tunalbe laser absorption spectroscopy technique with a Tm:YAP solid-state laser Liu Long, Wen-qiang Xie, Xiao-tao Yang ∗ College of Power and Energy Engineering, Institue of Marin Engine Electionic Control Technology, Harbin Engineering University, Harbin 150001, China
a r t i c l e
i n f o
Article history: Received 7 April 2016 Accepted 1 June 2016 Keywords: Tm:YAP Tunable Absorption spectroscopy Concentration
a b s t r a c t This work investigates a tunable laser absorption spectroscopy technique for the H2 O concentration by a Tm:YAP solid-state laser. The output wavelength of Tm:YAP laser is tuned by a birefringence filter and an F-P etalon in the laser cavity. The tuning range is from 1910 nm to 1914 nm, the tuning frequency is 1 Hz. With the tunable Tm:YAP laser, we realize a concentration resolution of 10 ppb. Different concentrations of H2 O vapor are use to test the precision of the system. A maximum relative error of 0.8% is realized. At the same time, we calculate the maximum absolute error to be 0.8 ppm. Up to the authors’ knowledge, it is the first time to report a tunable laser absorption spectroscopy for the gas concentration measurement by a Tm-doped laser. © 2016 Elsevier GmbH. All rights reserved.
1. Introduction Measurements of the gas concentration by tunable laser absorption spectroscopy have been demonstrated as an attractive technique, which has several advantages such as simple structure, good dynamic response, high precision, high resolution and so on [1–3]. Due to these advantages, TDLAS has good applications in many scopes, such as atmosphere monitoring [4,5] and combustion diagnose [6,7], which can realize the measurements of the temperature [8] and the flow velocity [9] also. Most of the systems use a diode laser source. In despite of the advantages of the diode lasers, there are some obvious disadvantages which limit the applications for them. The diode laser is very sensitive to the environment temperature, which will effect the laser output power as well as the laser spectrum. With the fluctuation of temperature, extra error may be taken into the measurements. As we know, the detection resolution is related to the laser output power. The output power of diode lasers are low in some waveband, which limits the remote measurement. Sometimes, the efficiency of diode laser are low. Compared with the diode lasers, there are several advantages for the solid-state lasers. The output characteristic are stable for the solid-state lasers, whose beam quality can be close to the diffraction-limited beam propagation. The efficiency is much higher than the one of the diode lasers. The great output power of the solid-state lasers can realize a remote measurement and higher resolution. The 2 m lasers are in the eye-safety wavelength regions, where include strong absorption lines of water. Therefore, it is expected to have potential applications in the concentration measurement of H2 O. Tm-doped lasers
∗ Corresponding author. E-mail address: [email protected] (X.-t. Yang). http://dx.doi.org/10.1016/j.ijleo.2016.06.001 0030-4026/© 2016 Elsevier GmbH. All rights reserved.
8278
L. Long et al. / Optik 127 (2016) 8277–8280
Fig. 1. The experimental setup of the tunable Tm:YAP laser.
Fig. 2. The experimental setup of the TSLAS.
have been demonstrated a good way to obtain the 2 m lasers, which have a high efficiency. With a reasonable the output power of the Tm lasers can reach more than 100W [10]. In this letter, we use a Tm:YAP laser to realize the H2 O concentration measurement. With a birefringence tuning plate and a Fabry-Perot etalon inserted, a tunable Tm:YAP laser is obtained. The tunable range is from 1910 nm to 1914 nm, which include a strong absorption of H2 O at temperature (1937.8 nm). Up to the authors’ knowledge, it is the first time to report a tunable laser absorption spectroscopy for the gas concentration measurement by a Tm-doped laser. 2. Experimental setup The tunable Tm:YAP laser experimental setup is shown in Fig. 1. The Tm:YAP crystal for the experiment is b-cut with dimensions of 3 × 3 × 8 mm3 , whose two end surfaces were AR-coated at both 795 nm(R < 0.5%) and 1.9 m (R < 0.3%). And the doped concentrations is 3 at.%. Tm:YAP crystal is wrapped in indium foil and hold in a copper heat-sink bonded on a thermal electric cooler (TEC) with precise temperature control, and Tm:YAP crystal was held at 20 ◦ C. The both pump source are 50 W laser diode, that output with a 400 m core-diameter pigtail fiber. The coupling lenses with 50 mm and 100 mm focuses are used to refocus the pump laser into the laser crystal. Pump-beam diameter is nearly 800 m at the laser crystal location. Two 45◦ dichroic mirror (R > 99.5% at 1.9 m and T∼99% at 795 nm) are used in the laser cavity. The birefringence filter is a 5mm-thick quartz plate, whose two end surfaces were AR-coated at 1.9 m (R < 0.3%). The F-P etalon is a 0.5mm-thick quartze plate, which is installed on the a rotating mirror to rotate at certain frequency. The output coupler is a plano-concave lens with a 100 mm radius of curvature, which is coated with 90% reflectivity at 1.9 m. The measurement chamber we use is a multi pass absorption cell, whose optical path length is 1 m. The maximum output power of Tm:YAP laser is 1W. We estimate the beam quality to be M2 = 1.1, which is close to diffraction-limited beam propagation. We use a InGaAs detector in this system. The laser beam shot on a diffuse reflection plate rather than directly on the detector to avoid saturation. The experimental setup of the system is shown in Fig. 2.
L. Long et al. / Optik 127 (2016) 8277–8280
8279
Power (W)
1.2
1.0
0.8
0.6 1910
1911
1912
1913
1914
Wavelength (nm) Fig. 3. The tuning curve of the Tm:YAP laser and the absorption spectrum of H2 O.
Fig. 4. The original signal of the Tm:YAP laser.
Fig. 5. The signal after absorption of H2 O vapor.
3. Experimental results We realize the output wavelength tuning by changing the angle of the F-P etalon. The tuning curve is shown in Fig. 3. We realize a continuous tuning from 1910 nm to 1914 nm, which matches a strong absorption line of H2 O. The frequency of the rotating mirror is 1 Hz. With an InGaAs we obtain the original signal of the tunable Tm:YAP laser, which is shown in Fig. 4. Different concentrations of calibrating water vapor are used to test the TSLAS (tunable solid-state laser absorption spectroscopy) system. Fig. 5 shows the signal from the detector after the absorption of H2 O vapor, when the concentration is
8280
L. Long et al. / Optik 127 (2016) 8277–8280
Table 1 The contrast of the measurement value and actual value of H2 O vapor. Standard gas volume concentration/ppmv
Experimental result/ppmv
The relative error/%
The Absolute error/ppm
10 50 100
10.08 50.34 100.8
+0.8 +0.68 +0.8
0.08 0.34 0.8
10ppmv. We can see that, the absorption is obvious. We calculate the concentration by the law of Beer-Lambert. When a monochromatic laser get through the gas, the intensity change can be expressed as it: It = I0 exp [−PS (T ) () XL] = exp [−˛ ()]
(1)
I0 is original laser intensity when there is no gas absorption. It is laser intensity after gas absorption. S(T) is the absorption line strength of the gas, which expresses the absorption intensity of the spectral line, only related to the temperature. P is the pressure of the gas medium. L is the propagation distance that a laser through in the gas. X is the volume concentration of the gas. Ф() is the linear function, which expresses the shape of the measured absorption lines, relating to the temperature, pressure and each component content in the gas. The calculated H2 O concentration is shown in Table 1. As we can see from the table, the experimental result tallies with the real value well. The maximum relative error is 0.8% for the 10 ppm H2 O concentration. However, the absolute error is only 0.08 ppm. The maximum absolute reaches 0.8 ppm, which can be attributed to the undulation of the laser power, the fitting accuracy and the background noise. With better processing method, we can obtain more accurate result. In this system, the concentration resolution can be calculated to 10 ppb. We can improve the resolution by increasing the optical length or adopt better algorithm. 4. Conclusion In summary, a tunable laser absorption spectroscopy technique for the H2 O concentration by a Tm:YAP solid-state laser is demonstrated. The tunable Tm:YAP laser is used in the TLAS technique for the first time. Compared with diode lasers, the solid-state lasers have several obvious advantages. The output power of the Tm:YAP laser is much higher than diode lasers, which can increase the detection resolution. The concentration resolution of the TSLAS system is calculated to 10 ppbv. With the system, we realize a maximum relative error of 0.8% and a maximum absolute error of 0.8 ppm. Acknowledgements This work was supported by NSFC (61405046, 51509051) and Natural Science Foundation of Heilongjiang (Grant No. 51305089, LC2015017). References [1] M.J. Nikkari, J. Di Iorio, J.M. Thomson, In situ combustion measurements of CO, H2 O, and temperature with a 1: 58 m diode laser and two-tone frequency modulation, Appl. Opt. 41 (44) (2002) 6–452. [2] A. Farooq, J.B. Jeffries, R.K. Hanson, Measurement of CO2 concentration and temperature at high pressures using 1f-normalized wavelength modulation spectroscopy with second harmonic detection near 2.7 m[J], Appl. Opt. 48 (2009) 6740–6753. [3] H. Teichert, T. Fernholz, V. Ebert, Simultaneous in situ measurement of CO, H2 O, and gas temperatures in a full-sized coal-fired power plant by near-infrared diode lasers, Appl. Opt. 42 (2003) 2043–2051. [4] N.D. Nevers, Air Pollution Control Engineering [M], 2nd edition, McGraw-Hill, New York, USA, 2000. [5] Fei Li, Xilong Yu, Weiwei Cai, Uncertainty in velocity measurement based on diode-laser absorption in nonuniform flows, Appl. Opt. 51 (2012) 4788–4797. [6] B.T. McClue, Charaeterization of the transient response of a diesel exhaust gas measurement system, SAE 13 (1988) 287–295. [7] Jingsong Li, Uwe Parchatka, Rainer Königstedt, Horst Fischer, Real-time measurements of atmospheric CO using a continuous-wave room temperature quantum cascade laser based spectrometer, Opt. Express 20 (2012) 7590–7600. [8] R.K. Hanson, P.A. Kuntz, C.H. Kruger, High-resolution spectroscopy of combustion gases using a tunable ir diode laser, Appl. Opt. 16 (1977) 2045–2048. [9] Fei Li, Xilong Yu, Weiwei Cai, Lin Ma, Uncertainty in velocity measurement based on diode-laser absorption in nonuniform flows, Appl. Opt. 51 (2012) 4789–4797. [10] P.B. Meng, B.Q. Yao, Y.L. Ju, Y.Z. Wang, Power scaling of end-pumped c-cut Tm:YAP lasers, Laser Phys. 23 (2013) 1167–1171.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Measurement of H2 O concentration by tunalbe laser absorption spectroscopy technique with a Tm:YAP solid-state laser Liu Long, Wen-qiang Xie, Xiao-tao Yang ∗ College of Power and Energy Engineering, Institue of Marin Engine Electionic Control Technology, Harbin Engineering University, Harbin 150001, China
a r t i c l e
i n f o
Article history: Received 7 April 2016 Accepted 1 June 2016 Keywords: Tm:YAP Tunable Absorption spectroscopy Concentration
a b s t r a c t This work investigates a tunable laser absorption spectroscopy technique for the H2 O concentration by a Tm:YAP solid-state laser. The output wavelength of Tm:YAP laser is tuned by a birefringence filter and an F-P etalon in the laser cavity. The tuning range is from 1910 nm to 1914 nm, the tuning frequency is 1 Hz. With the tunable Tm:YAP laser, we realize a concentration resolution of 10 ppb. Different concentrations of H2 O vapor are use to test the precision of the system. A maximum relative error of 0.8% is realized. At the same time, we calculate the maximum absolute error to be 0.8 ppm. Up to the authors’ knowledge, it is the first time to report a tunable laser absorption spectroscopy for the gas concentration measurement by a Tm-doped laser. © 2016 Elsevier GmbH. All rights reserved.
1. Introduction Measurements of the gas concentration by tunable laser absorption spectroscopy have been demonstrated as an attractive technique, which has several advantages such as simple structure, good dynamic response, high precision, high resolution and so on [1–3]. Due to these advantages, TDLAS has good applications in many scopes, such as atmosphere monitoring [4,5] and combustion diagnose [6,7], which can realize the measurements of the temperature [8] and the flow velocity [9] also. Most of the systems use a diode laser source. In despite of the advantages of the diode lasers, there are some obvious disadvantages which limit the applications for them. The diode laser is very sensitive to the environment temperature, which will effect the laser output power as well as the laser spectrum. With the fluctuation of temperature, extra error may be taken into the measurements. As we know, the detection resolution is related to the laser output power. The output power of diode lasers are low in some waveband, which limits the remote measurement. Sometimes, the efficiency of diode laser are low. Compared with the diode lasers, there are several advantages for the solid-state lasers. The output characteristic are stable for the solid-state lasers, whose beam quality can be close to the diffraction-limited beam propagation. The efficiency is much higher than the one of the diode lasers. The great output power of the solid-state lasers can realize a remote measurement and higher resolution. The 2 m lasers are in the eye-safety wavelength regions, where include strong absorption lines of water. Therefore, it is expected to have potential applications in the concentration measurement of H2 O. Tm-doped lasers
∗ Corresponding author. E-mail address: [email protected] (X.-t. Yang). http://dx.doi.org/10.1016/j.ijleo.2016.06.001 0030-4026/© 2016 Elsevier GmbH. All rights reserved.
8278
L. Long et al. / Optik 127 (2016) 8277–8280
Fig. 1. The experimental setup of the tunable Tm:YAP laser.
Fig. 2. The experimental setup of the TSLAS.
have been demonstrated a good way to obtain the 2 m lasers, which have a high efficiency. With a reasonable the output power of the Tm lasers can reach more than 100W [10]. In this letter, we use a Tm:YAP laser to realize the H2 O concentration measurement. With a birefringence tuning plate and a Fabry-Perot etalon inserted, a tunable Tm:YAP laser is obtained. The tunable range is from 1910 nm to 1914 nm, which include a strong absorption of H2 O at temperature (1937.8 nm). Up to the authors’ knowledge, it is the first time to report a tunable laser absorption spectroscopy for the gas concentration measurement by a Tm-doped laser. 2. Experimental setup The tunable Tm:YAP laser experimental setup is shown in Fig. 1. The Tm:YAP crystal for the experiment is b-cut with dimensions of 3 × 3 × 8 mm3 , whose two end surfaces were AR-coated at both 795 nm(R < 0.5%) and 1.9 m (R < 0.3%). And the doped concentrations is 3 at.%. Tm:YAP crystal is wrapped in indium foil and hold in a copper heat-sink bonded on a thermal electric cooler (TEC) with precise temperature control, and Tm:YAP crystal was held at 20 ◦ C. The both pump source are 50 W laser diode, that output with a 400 m core-diameter pigtail fiber. The coupling lenses with 50 mm and 100 mm focuses are used to refocus the pump laser into the laser crystal. Pump-beam diameter is nearly 800 m at the laser crystal location. Two 45◦ dichroic mirror (R > 99.5% at 1.9 m and T∼99% at 795 nm) are used in the laser cavity. The birefringence filter is a 5mm-thick quartz plate, whose two end surfaces were AR-coated at 1.9 m (R < 0.3%). The F-P etalon is a 0.5mm-thick quartze plate, which is installed on the a rotating mirror to rotate at certain frequency. The output coupler is a plano-concave lens with a 100 mm radius of curvature, which is coated with 90% reflectivity at 1.9 m. The measurement chamber we use is a multi pass absorption cell, whose optical path length is 1 m. The maximum output power of Tm:YAP laser is 1W. We estimate the beam quality to be M2 = 1.1, which is close to diffraction-limited beam propagation. We use a InGaAs detector in this system. The laser beam shot on a diffuse reflection plate rather than directly on the detector to avoid saturation. The experimental setup of the system is shown in Fig. 2.
L. Long et al. / Optik 127 (2016) 8277–8280
8279
Power (W)
1.2
1.0
0.8
0.6 1910
1911
1912
1913
1914
Wavelength (nm) Fig. 3. The tuning curve of the Tm:YAP laser and the absorption spectrum of H2 O.
Fig. 4. The original signal of the Tm:YAP laser.
Fig. 5. The signal after absorption of H2 O vapor.
3. Experimental results We realize the output wavelength tuning by changing the angle of the F-P etalon. The tuning curve is shown in Fig. 3. We realize a continuous tuning from 1910 nm to 1914 nm, which matches a strong absorption line of H2 O. The frequency of the rotating mirror is 1 Hz. With an InGaAs we obtain the original signal of the tunable Tm:YAP laser, which is shown in Fig. 4. Different concentrations of calibrating water vapor are used to test the TSLAS (tunable solid-state laser absorption spectroscopy) system. Fig. 5 shows the signal from the detector after the absorption of H2 O vapor, when the concentration is
8280
L. Long et al. / Optik 127 (2016) 8277–8280
Table 1 The contrast of the measurement value and actual value of H2 O vapor. Standard gas volume concentration/ppmv
Experimental result/ppmv
The relative error/%
The Absolute error/ppm
10 50 100
10.08 50.34 100.8
+0.8 +0.68 +0.8
0.08 0.34 0.8
10ppmv. We can see that, the absorption is obvious. We calculate the concentration by the law of Beer-Lambert. When a monochromatic laser get through the gas, the intensity change can be expressed as it: It = I0 exp [−PS (T ) () XL] = exp [−˛ ()]
(1)
I0 is original laser intensity when there is no gas absorption. It is laser intensity after gas absorption. S(T) is the absorption line strength of the gas, which expresses the absorption intensity of the spectral line, only related to the temperature. P is the pressure of the gas medium. L is the propagation distance that a laser through in the gas. X is the volume concentration of the gas. Ф() is the linear function, which expresses the shape of the measured absorption lines, relating to the temperature, pressure and each component content in the gas. The calculated H2 O concentration is shown in Table 1. As we can see from the table, the experimental result tallies with the real value well. The maximum relative error is 0.8% for the 10 ppm H2 O concentration. However, the absolute error is only 0.08 ppm. The maximum absolute reaches 0.8 ppm, which can be attributed to the undulation of the laser power, the fitting accuracy and the background noise. With better processing method, we can obtain more accurate result. In this system, the concentration resolution can be calculated to 10 ppb. We can improve the resolution by increasing the optical length or adopt better algorithm. 4. Conclusion In summary, a tunable laser absorption spectroscopy technique for the H2 O concentration by a Tm:YAP solid-state laser is demonstrated. The tunable Tm:YAP laser is used in the TLAS technique for the first time. Compared with diode lasers, the solid-state lasers have several obvious advantages. The output power of the Tm:YAP laser is much higher than diode lasers, which can increase the detection resolution. The concentration resolution of the TSLAS system is calculated to 10 ppbv. With the system, we realize a maximum relative error of 0.8% and a maximum absolute error of 0.8 ppm. Acknowledgements This work was supported by NSFC (61405046, 51509051) and Natural Science Foundation of Heilongjiang (Grant No. 51305089, LC2015017). References [1] M.J. Nikkari, J. Di Iorio, J.M. Thomson, In situ combustion measurements of CO, H2 O, and temperature with a 1: 58 m diode laser and two-tone frequency modulation, Appl. Opt. 41 (44) (2002) 6–452. [2] A. Farooq, J.B. Jeffries, R.K. Hanson, Measurement of CO2 concentration and temperature at high pressures using 1f-normalized wavelength modulation spectroscopy with second harmonic detection near 2.7 m[J], Appl. Opt. 48 (2009) 6740–6753. [3] H. Teichert, T. Fernholz, V. Ebert, Simultaneous in situ measurement of CO, H2 O, and gas temperatures in a full-sized coal-fired power plant by near-infrared diode lasers, Appl. Opt. 42 (2003) 2043–2051. [4] N.D. Nevers, Air Pollution Control Engineering [M], 2nd edition, McGraw-Hill, New York, USA, 2000. [5] Fei Li, Xilong Yu, Weiwei Cai, Uncertainty in velocity measurement based on diode-laser absorption in nonuniform flows, Appl. Opt. 51 (2012) 4788–4797. [6] B.T. McClue, Charaeterization of the transient response of a diesel exhaust gas measurement system, SAE 13 (1988) 287–295. [7] Jingsong Li, Uwe Parchatka, Rainer Königstedt, Horst Fischer, Real-time measurements of atmospheric CO using a continuous-wave room temperature quantum cascade laser based spectrometer, Opt. Express 20 (2012) 7590–7600. [8] R.K. Hanson, P.A. Kuntz, C.H. Kruger, High-resolution spectroscopy of combustion gases using a tunable ir diode laser, Appl. Opt. 16 (1977) 2045–2048. [9] Fei Li, Xilong Yu, Weiwei Cai, Lin Ma, Uncertainty in velocity measurement based on diode-laser absorption in nonuniform flows, Appl. Opt. 51 (2012) 4789–4797. [10] P.B. Meng, B.Q. Yao, Y.L. Ju, Y.Z. Wang, Power scaling of end-pumped c-cut Tm:YAP lasers, Laser Phys. 23 (2013) 1167–1171.