High-Spectral-Resolution Two-photon Pump Polarization Spectroscopy Probe (TPP-PSP) Technique for Measurements of Atomic Hydrogen

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1 High-Spectral-Resolution Two-photon Pump Polarization Spectroscopy Probe (TPP-PSP) Technique for Measurements of Atomic Hydrogen Aman Satija, Aizaz H. Bhuiyan and Robert P. Lucht. School of Mechanical Engineering Purdue University West Lafayette, IN

2 Outline Motivation Background TPP-PSP using two single mode OPG/PDA laser systems Results TPP-PSP using a simplified dye laser system Density Matrix Modeling

3 Motivation H-atom is key species in combustion due to its high reactivity and diffusivity. Conventional incoherent techniques (i.e. multiphoton LIF) offer low signal levels, are susceptible to collisional quenching and suffer from specie interferences. Non-linear coherent technique such as Laser Induced Polarization Spectroscopy (LIPS) offers high sensitivity and lower collisional susceptibility. Quantitative measurements require understanding of laser-specie interaction including saturation and Stark effect to obtain the value of beam energies which optimize H atom detection. Variation of LIPS called TPP-PSP used in our experiments.

4 243 nm Pump 243 nm Pump Two-photon Pump Polarization Spectroscopy Probe (TPP-PSP) Technique 656 nm Pump 656 nm Probe 656 nm Signal 3 P 1/2,3/2 M= -3/2 M= -1/2 3 P 3/2 M= +1/2 M= +3/2 2 S 1/2 M= -1/2 M= +1/2 2 S 1/2 M= -1/2 3 P 1/2 M= +1/2 M= -1/2 M= +1/2 2 S 1/2 1 S 1/2 TPP-PSP for H-atom Both pump and probe lasers used in TPP-PSP experiment are single-mode, narrow linewidth and tunable over wide range. OPG/PDA systems are used to generate these laser beams. Pump RCP Probe RCP Probe LCP 2 S 1/2-3 P 1/2 and 2 S 1/2-3 P 3/2 transitions

5 OPG/PDA Optical Parametric Generation (OPG): ω 3 - Pump ω 2 - Idler ω 1 - Signal Signal beam b-bbo Crystals Pump beam Seed beam DFB ω 3 ω 2 Pulsed Dye Amplification (PDA): ω 1 Injection seeding at idler wavelength increases the signal intensity by several times OP linewidth cm -1. OPG signal in not strong enough for typical applications Solid-state amplification is complex and expensive PDA is simple and less expensive 656-nm signal beam Dye Cell 355 nm Pump beam Dye Cell 532-nm pump beam +ve Lens Longitudinal Pumping 486 nm beam (+) ve Cylindrical Lens (-) ve Cylindrical Lens Transverse Pumping

6 PMT Experimental System 656 nm PDA 2 Delay Line BS BD b-bbo Crystals 532 nm BC: Beam Combiner; BD: Beam Dump; BS: Beam Splitter; CL: Cylindrical Lens; DFB: Distributed Feedback Diode Laser; IF: Interference Filter; l/2: Half-wave-plate; M1, M2, M3: Zero Degree Mirrors; OPG: Optical Parametric Generator; PD: Photodiode; PDA1, PDA2: Pulsed Dye Amplifier (LD489 Dye) Longitudinal Pumping; PDA3, PDA4, PDA5: Pulsed Dye Amplifier (DCM Dye); Side Pumping; Pol: Polarizer; T: Telescope Pol. l/2 M1 PDA 1 M2 CL BD 772 nm (c) Sacher DFB Faraday Isolator Typical : UV pump energy mj/pulse 656 pump : 100 nj- 1µJ/pulse 656 probe < 50 nj/pulse T 355 nm OPG 656 nm IF Andor Idus BD Hencken Burner PD Pol. Pol. 656 nm L l/2 OPG 656 nm Delay Line l/2 M3 355 nm 772 nm Sacher DFB Seeded Nd:YAG Pro-290 To WEX T PDA 5 BS PDA 4 PDA 3 Pump for OPG 656 nm T BS OPG 486 nm BS BS L Pol. PD BC Pol. l/2 l/4 L Pol. 243 nm WEX 486 nm OPG 486 nm 1330 nm NEL DFB T BD b-bbo Crystals T BD 486 nm NEL DFB 1330 nm T Pol. l/2 355 nm A. Bhuiyan, A. Satija, S. V. Naik, R. P. Lucht. Opt. Lett. Vol. 37 (2012)

7 Overall TPP-PSP Experimental System (contd.) Overall System 656-nm PDA 486-nm PDA

8 Experimental System (cont.) Non-premixed, 2-D, near adiabatic flat flame Hencken burner Top of burner has a honeycomb matrix : 36.5 mm square Co-flow of N 2 (50.8 mm square) to prevent shear instabilities

9 Effect of 243-nm Pump Pulse Energy Variation on Lineshapes for n = 2 to n = 3 Transitions 656-nm Pump Pulse Energy: 100 nj/pulse TPP-PSP lines broaden and Stark shift with increasing 243-nm pump beam energy.

10 Effect of 656-nm Pump Pulse Energy Variation on Lineshapes for n = 2 to n = 3 Transitions 243-nm Pump Pulse Energy: 0.3 mj/pulse TPP-PSP lines broaden and appearance of a dip with increasing 656-nm pump beam energy.

11 Detection Limit Adiabatic equilibrium H- atom concentration at equivalence ratio of 0.65: 11 parts per million (ppm) Measurement Location: 25 mm above burner surface.

12 243 nm Pump 243 nm Pump Energy Level diagram Balmer β transition for TPP- PSP 4 P 1/2,3/2 M = -3/2 M = -1/2 4 P 3/2 M = +1/2 M = +3/2 486 nm Pump 486 nm Probe 486 nm Signal 2 S 1/2 M = -1/2 M = +1/2 2 S 1/2 M = -1/2 4 P 1/2 M = +1/2 1 S 1/2 Pump RCP M = -1/2 M = +1/2 2 S 1/2 Probe RCP Probe LCP 2 S 1/2-4 P 1/2 and 2 S 1/2-4 P 3/2 transitions

13 Un-seeded Nd:YAG Schematic for using Balmer β transition for TPP-PSP Band-Pass PMT Mirror POL High Speed Shutter Probe Flame Digital Oscilloscope 355 nm POL 243 nm Two- photon pump Fresnel Rhomb 486 nm SHG Narrowband Dye Laser POL l/2

14 Compact Experimental Setup for H atom TPP-PSP

15 Signal From PMT (Volt) TPP-PSP Signal using Balmer β transition Chemiluminescence UV Pump Only Probe Leakage LIPS Raw Signal Final Signal Calculated H atom mole-fraction at measurement location = 2%. at 3000 K Oscilloscope Axis

16 Nonperturbative Modeling of TPP-PSP of H atom Liouville formulation from the Schrödinger wave equation (SWE) i i V jk jk j k jm mk jm mk m m i V jj jm mj jm mj m m V V is proportional to the degree of coherence that exists between two quantum states j and k is proportional to the population of quantum state j.

17 Energy Level Structure and Collisional transfer 3P 3/2 3P 1/2 3S 1/2 3D 3/2 3D 5/2 2P 3/2 2S 1/2 2P 1/2 Fast Collisional Transfer 1S 1/2

18 Acknowledgement OPG/PDA system was aligned by Dr. Aizaz Bhuiyan. Funding for this research was provided by the U.S. Department of Energy, Division of Chemical Sciences, Geosciences and Biosciences, under Grant No. DE-FG02-03ER15391.

19 Thank You!