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1 Downloaded from orbit.dtu.dk on: Oct 30, 2019 Parametric Processes for Generation and Low Noise Detection of Infrared Light Experimental and Numerical Investigation of Fundamental Parameters for the Design of PPLN-based Light Sources and Detector Systems Høgstedt, Lasse Publication date: 2016 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Høgstedt, L. (2016). Parametric Processes for Generation and Low Noise Detection of Infrared Light: Experimental and Numerical Investigation of Fundamental Parameters for the Design of PPLN-based Light Sources and Detector Systems. Technical University of Denmark. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

2 Ph.D. Thesis Parametric Processes for Generation and Low Noise Detection of Infrared Light Experimental and Numerical Investigation of Fundamental Parameters for the Design of PPLN-based Light Sources and Detector Systems. Lasse Høgstedt DTU Risø Campus 2016

3 b

4 Summary

5 ii Summary 2

6 Resumé

7 iv Resumé 2

8 Preface Acknowledgements

9 vi

10 First Author List of Publications 2

11 viii List of Publications Co-author Supervised Master Projects µ

12 Contents

13 x Contents 2

14 CHAPTER 1 Introduction 1.1 Project Goals

15 2 1 Introduction 1.2 Motivation CO 4.6 Pulse energy CW power 1 kj 1 kw F 2 excimer 157 nm ArF excimer 193 nm th Nd:YAG (5 harmonic) 213 nm + He-Ag nm KrCl excimer 222 nm KrF excimer 248 nm th Nd:YAG (4 harmonic) 266 nm XeCl excimer 308 nm He-Cd 325 nm + Nitrogen nm Ne nm XeF excimer 351 nm Ruby (doubled) 347 nm 2+ Nd:YAG (tripled) 355 nm Ar 351 nm He-Cd nm + Ar nm Copper vapor nm + Ar nm Nd:YAG (doubled) 532 nm 3+ He-Ne nm Xe nm Copper vapor nm He-Ne nm He-Ne nm He-Ne nm Gold vapor 628 nm + Kr nm Ruby nm Downconversion Nd:YAG 946 nm Nd:YAG 1064 nm (other hosts nm) He-Ne 1152 nm Iodine 1315 nm Nd:YAG 1319 nm He-Ne 1523 nm Er:glass 1.54 µm Tm:YAG 2.01 µm Ho:YAG 2.08 µm Er:YSGG 2.79 µm Er:YAG 2.90, 2.94 µm He-Ne µm CO µm Methanol 37.9, 70.5, 96.5, 118 µm Methylamine µm Methyl fluoride 496 µm Methanol 571, 699 µm 1 J 1 W 1 mj 1 mw FAR-IR 1 mj 1 mw Ti:sapphire 1 J 1 W (tripled) nm 1 kj 1 kw CO (doubled) µm ULTRAVIOLET VISIBLE NEAR-INFRARED MID-INFRARED 200 nm 300 nm 400 nm 500 nm 600 nm 700 nm 800 nm 900 nm 2 1 µm 3 µm 10 µm 30 µm 1 mm Dyes in polymer InGaAs Xe-He nm nm 2-4 µm Dyes CO 2 (doubled) + He-Au µm µm + Ti:sapphire Ne-Cu nm InGaAlP CO nm Alexandrite (doubled) nm Cr fluoride 5-7 µm (doubled) nm nm Alexandrite InGaAs Dyes (doubled) DF chemical nm GaN nm µm µm µm InGaN nm GaAlAs µm Ti:sapphire Fosterite nm HF chemical nm nm µm µm AlGaIn/AsSb µm Dyes (Raman shifted) µm Pb salts µm CO µm

16 1.3 Prior Work 3 µ 1.3 Prior Work

17 4 1 Introduction The Pioneering Years µ P s = (βlp p /b)πθ 2 β = 2ν4 s ν i d 2 15 n s (2π) 2 ϵ 3 0 c5 n i n p

18 1.3 Prior Work 5 ν j n j d 15 L P p b ɛ 0 c (πθ 2 ) 3

19 6 1 Introduction Recent Advances Within Upconversion Detection µ µ µ 2 µ

20 1.3 Prior Work Light Sources

21 8 1 Introduction

22 1.3 Prior Work 9 µ 4

23 10

24 CHAPTER 2 Physics and Technology 2.1 Nonlinear Interaction λ = λ λ ( ) λ = λ + λ ( )

25 12 2 Physics and Technology

26 2.1 Nonlinear Interaction Coupled Field Equations da 1 dz = iga 3a 2 ( i k(t,λ,θ)z) da 2 dz = iga 3a 1 ( i k(t,λ,θ)z) da 3 dz = iga 1a 2 (i k(t,λ,θ)z) g 2 = ϵ µ n 1 n 2 n 3 2 d 2 ω 1 ω 2 ω 3, I j = ω j a j 2 k = k 3 k 2 k 1, k j = 2π λ j n j (λ j,t ) n j λ j T µ 0 z ω j k d eff ϵ 2 0 g 2 a 3 a 2 a 1

27 14 2 Physics and Technology I j Conversion Efficiency I j ( ) I 3 (L) = I 1 (0)I 2 (0) g 2 ω 3 k(t,λ,θ)l L 2 2 ω 1 ω }{{ 2 2π }}{{} η η k η 1 3 = I 3(L) I 1 (0) = I 2(0)η k η η 1 3 = I 3(L) I 1 (0) = I 2(0)η k η η η η 1 η η k η 1 3

28 2.1 Nonlinear Interaction 15 QE 1 3 = ω 1 ω 3 η 1 3 a 1 a 3 k = 0 η 1 3 = I 3(L) I 1 (0) = ω 3 2 γl ω 1 2, γ2 = 4g 2 I 2 = 8ω 1 ω 2 I 3 d 2 ϵ µ ω 2 n 1 n 2 n 3 g a 1 a 2 k = 0 G 0 L = I j(l) I j (0) = 2 ( ) γl, γ 2 = 4g 2 I 3 2 ω 3 j = 1 j = 2 k Numerical Implementation

29 16 2 Physics and Technology π Gaussian Beam Considerations

30 2.2 Phasematching Phasematching kl k = k 3 k 2 (θ 2 ) k 1 (θ 1 )

31 18 2 Physics and Technology ( ) k1 θ 2 = (θ 1 ) k 1 θ 1, θ 1 1 k 2 k 2 [ k k 3 k ( ) ] 2 ( ) k1 θ 1 k 1 1 θ2 1 2 k 2 2 δ k δ k = k θ k = ± 1 ( ) k θ2 1 + k 1 k 2 θ1 = 2 4π L ( ) k k 1 k 2 θ ) sinc 2( kl 2π FWHM ± k(t,θ j,λ j)l 2π k

32 2.2 Phasematching 19 l coh = 2π k Λ/ Quasi-phasematching Λ

33 20 2 Physics and Technology l coh = Λ 2/π k = k 3 k 2 k 1 ± 2π Λ = k 3 k 2 k 1 ± k qpm

34 2.2 Phasematching 21 k qpm k 0 k K-space Approach to Phasematching k k

35 22 2 Physics and Technology da dz = iga a (idkz) L a = ig a a dzd(z) (idkz), 0 g = g(z) d(z) L 0 dzd(z) (idkz) = d eff,ideal L d eff,ideal d (z) d (z) = d(z) d eff,ideal a = ig a a Ld eff,ideal (d (z)) I = 2ω2 ϵ µ n n n d 2 eff,ideall 2 I I (d (z)) 2 η (d (z)) 2 η k

36 2.3 Periodically Poled Lithium Niobate Periodically Poled Lithium Niobate µ µ Poling Procedure µ Types of Poling Errors

37 24 2 Physics and Technology

38 2.3 Periodically Poled Lithium Niobate 25

39 26

40 CHAPTER 3 Light Source Configuration 3.1 Cavity Design of The Parametric Module 00 µ µ 2

41 28 3 Light Source Configuration

42 3.1 Cavity Design of The Parametric Module

43 30 3 Light Source Configuration 3.2 Design and Test of a MIR Optical Parametric Generator µ µ 35 µ Temporal Pulse Distortion

44 3.2 Design and Test of a MIR Optical Parametric Generator 31

45 32 3 Light Source Configuration

46 3.2 Design and Test of a MIR Optical Parametric Generator 33

47 34 3 Light Source Configuration I (L, 0) 1 ( ) γ(t)l 2 = I (0, 0) 2 I (0, 0) (γ(t)l) ( ) γ(t) = γ(0) t 2 4 (2) 2 γl 1 γ(t, r) I (Z, 0) L = ( 2 1 (2) ) 2 γ(0)l γ

48 3.2 Design and Test of a MIR Optical Parametric Generator Average power Peak power 250 Average power@3330 nm [mw] Peak power@3330 nm [W] Average OPG mixing 1064 nm [mw] Vacuum Fluctuations as OPA Seed

49 36 3 Light Source Configuration ( ) 2 γl ϕ (0, 0) = ϕ (L, 0) 2 ϕ j = Ij ω j γl = 25 ϕ (0, 0) = µ ϕ,calc (0, 0) = 2 n3 2π ω 22 = ω

50 3.2 Design and Test of a MIR Optical Parametric Generator Peak intensity [MW/cm 2 ] NIR at 1598 nm MIR at 3300 nm Mix at 1064 nm Crystal length [mm] µ Depletion in the Upconversion Process 4

51 38 3 Light Source Configuration 1.0 A 1.2 A 1.4 A Intensity [a.u.] Depletion=74.9 % Osc. freq.=116 khz Depletion=77.6 % Osc. freq.=167 khz Depletion=82.3 % Osc. freq.=210 khz Time [µs] Time [µs] Time [µs] 1.6 A 1.8 A 2.0 A Intensity [a.u.] Depletion=91.1 % Osc. freq.=233 khz Depletion=92.2 % Osc. freq.=281 khz Depletion=89 % Osc. freq.=300 khz Time [µs] Time [µs] Time [µs] 2.2 A 2.4 A 2.6 A Intensity [a.u.] Depletion=87.8 % Osc. freq.=343 khz Depletion=87.6 % Osc. freq.=358 khz Depletion=85.3 % Osc. freq.=410 khz Time [µs] Time [µs] Time [µs] 2.8 A 3.0 A Intensity [a.u.] Depletion=86.5 % Osc. freq.=415 khz Depletion=84.6 % Osc. freq.=467 khz Cavity power Input pulse Time [µs] Time [µs]

52 3.2 Design and Test of a MIR Optical Parametric Generator Spectral Output Characteristics µ

53 40 3 Light Source Configuration λ c Λ µ Λ µ µ µ µ k

54 3.3 OPA Measurements OPA Measurements 3. 0 O u t p u t p o w e r [ m W ] M e a s u r e m e n t d a t a ( 5 % e r r o r b a r s ) S e c o n d o r d e r p o l y n o m i a l f i t W a v e l e n gµm t h ] [

55 42 3 Light Source Configuration λ c = 3190 λ c = 1598 λ c = 1064 E 1064 = 74µ E 3190 = 5µ

56 3.3 OPA Measurements 43 µ NIR-seed a) Output 1: With NIR-seed d) Intensity [dbm] 70 Intensity [dbm] Wavelength [nm] Wavelength [nm] Intensity [dbm] OPA mixing laser b) Intensity [dbm] Output 2: No seed e) Wavelength [nm] Wavelength [nm] Calculated MIR seed c) Output 3: With MIR-seed f) Intensity [dbm] Intensity [dbm] Wavelength [nm] Wavelength [nm]

57 44 3 Light Source Configuration Pulse Duration with Seed 1 w = 1 = w w Choice of Light Source Technology for Remote Detection

58 3.4 Choice of Light Source Technology for Remote Detection 45 2 µ

59 46

60 CHAPTER 4 Detector Configuration 4.1 Upconversion Module as Detector

61 48 4 Detector Configuration µ µ µ µ µ µ

62 4.1 Upconversion Module as Detector 49 Wavelength [nm] Temperature [ C] Bandwidth [nm] Wavelength [nm] Temperature [ C] Wavelength [nm] Temperature [ C] Wavelength [nm] µ µ µ Wavelength [nm] Bandwidth [nm] Wavelength [nm] Temperature [ C] Wavelength [nm] Temperature [ C] Temperature [ C] Wavelength [nm] µ µ µ

63 50 4 Detector Configuration Second Generation Module

64 4.1 Upconversion Module as Detector 51

65 52 4 Detector Configuration 4.2 Upconversion Noise µ µ

66 4.2 Upconversion Noise µ

67 54 4 Detector Configuration 4 µ µ µ Upconverted SPDC Noise

68 4.2 Upconversion Noise 55 Intensity [counts] T= 30 C T= 60 C T=130 C Wavelength [nm] 11.8 µ

69 56 4 Detector Configuration Simultaneous Phasematch Noise Enhancement θ 1

70 4.2 Upconversion Noise 57 k = k φ 1 + k k θ 1 k k = k φ 2 k + k φ 1 k k + k = 2k + 2k φ 1 k θ 1 + k φ 2 θ 1 ( ) k θ 2 = π θ 1 k φ 1 = π θ 2 ( ) k φ 2 = φ 1 k π 11.8 µ 140 θ 1 = 50 ϕ 1 = 118

71 58 4 Detector Configuration ) SPDC process k spdc ) Upconversion process k up 6 5 λ VIS [nm] ) Semi-simultaneous phasematch k up + k spdc ) Super phasematch k up + k spdc 6 5 λ VIS [nm] θ 1 [mrad] θ 1 [mrad] 11.8 µ 140

72 4.3 Signal-to-noise Ratio Optimization µ 4.3 Signal-to-noise Ratio Optimization

73 60 4 Detector Configuration = 1 =, D = 1 Ad f D = D A d f Intensity Optimization

74 4.3 Signal-to-noise Ratio Optimization 61 > = σ2 σ 2, 2 =, 3 = σ

75 62 4 Detector Configuration 2 2 Noise [photons/second] A) Measurement fit to "ax 2 +b" Intensity [kw/cm 2 ] Internal quantum efficiency B) 0.2 Measurement Calculation Intensity [kw/cm 2 ] 100 C) Signal-to-noise ratio SNR 3 10 SNR 1 10 SNR Intensity [kw/cm 2 ] 50 µ 12

76 4.3 Signal-to-noise Ratio Optimization Investigation of the USPDC Grating Specificity Measurements of the RDC-errors on the Poled Grating 0.66 µ 2 2 Cross section of a PPLN crystal surface (Λ=11.8 µm) Etching depth [ µm ] Crystal position [mm]

77 64 4 Detector Configuration Quantum efficiency ( FFT 2 ) % RDC error 12% RDC error Measured grating k(t,λ,θ) k K µ 11.8 µ 6.0 ± 0.7 µ 6.0 ± 0.6 µ µ

78 4.3 Signal-to-noise Ratio Optimization Distribution of low-domains Histogram Gaussian fit Histogram Gaussian fit Distribution of high-domains Number of occurrences Number of occurrences Domain length [m] Domain length [m] 10-6 Λ = 11.8µ

79 66 4 Detector Configuration FFT Based Simulation 2 P = 1 N z P η N z 1 η η P = ω ω 4 nω d 2 π 2 c 5 n n ϵ 0 L 2 P dω φ 2 dφ 2 η η up η 2 dω φ 2 φ 2 = dφ 2

80 4.3 Signal-to-noise Ratio Optimization 67 ± λ ϕ 2

81 68 4 Detector Configuration FFT-based model RDC=12% (Worst case) RDC=12% (Mean) RDC=12% (Best case) RDC= 0% Photons [s -1 ] λ VIS [nm] µ Slab-by-slab model RDC=12% (Single run) RDC= 0% Photons [s -1 ] λ VIS [nm]

82 4.3 Signal-to-noise Ratio Optimization Slab-by-slab Simulation da dz da dz da dz = ig a a ( i k z) ig a a ( i k z) = ig a a ( i k z) = ig a a (i k z) ig a a ( i k z) da dz = ig a a (i k z) g k ck 2 a = dk φ 1 dφ 1 4π 2 n φ 1 φ 1 = dφ 1 dk

83 70 4 Detector Configuration Temperature Dependence of Upconverted SPDC Noise

84 4.3 Signal-to-noise Ratio Optimization Grating A (11.8µm), BP: 600nm-700nm, 1 Grating A (11.8µm), BP: 600nm-700nm, 1 Grating A (11.8µm), BP: 627nm-637nm, 30 Grating B (11.8µm), BP: 627nm-637nm, 90 Noise photons [s -1 ] Temperature [ C] 2 µ µ

85 72 4 Detector Configuration 1 st run, grating A (13.8µm) 2 nd run, grating A (13.8µm) 1st run, grating B (13.8µm) 1 10 Normalized intensity Cavity leak [mw] Temperature [ C] Temperature [ C] 400

86 4.3 Signal-to-noise Ratio Optimization 73 Noise photons [s -1 ] SBS-model 1 FFT-model Temperature [ C]

87 74 4 Detector Configuration Long Wavelength Mixing µ

88 4.3 Signal-to-noise Ratio Optimization 75 µ µ

89 76 4 Detector Configuration

90 CHAPTER 5 Application Tests of the Upconversion Technology 2

91 78 5 Application Tests of the Upconversion Technology 5.1 Low Noise mid-ir Upconversion Detector for Improved IR-DFWM Gas Sensing Introduction

92 5.1 Low Noise mid-ir Upconversion Detector for Improved IR-DFWM Gas Sensing Experimental Setup

93 80 5 Application Tests of the Upconversion Technology BOXCAR plates Pulsed Mid-IR source Pump 1 Probe Signal 2 4' 4 3 Pump 1' 3' 2' 500 mm 500 mm 200 mm 200 mm Flip Fourier space mirror spatial filter MIR C 2H 2 + N 2 f=500 mm f=200 mm Cryogenic InSb detector Germanium window LD [880 nm] Upconversion Detector PP:LN long pass 750 nm VIS Pump Nd:YVO 4 short pass 1000 nm short pass 850 nm EM- CCD f16 lens

94 5.1 Low Noise mid-ir Upconversion Detector for Improved IR-DFWM Gas Sensing Spectral Measurements 1 2 Wave number Wave number Scattering Data pixels Detected signal photons per pixel per pulse (VIS) ppm C 2 H ppm C 2 H ppm C 2 H 2 Simulation at 2 ppm Signal photons per pixel per pulse (MIR) 2 nd 1 st Wavenumber [cm 1 ]

95 82 5 Application Tests of the Upconversion Technology 1 η = η η η = = η η η Concentration Measurements y = ax k

96 5.1 Low Noise mid-ir Upconversion Detector for Improved IR-DFWM Gas Sensing 83 k k

97 84 5 Application Tests of the Upconversion Technology 2 2 ± ± ± ± ± ± ± ± ± ± ± Conclusion

98 5.2 Upconversion-based Long-range CO 2 DIAL Measurements Upconversion-based Long-range CO 2 DIAL Measurements Introduction 2 4 µ 2 1 λ = 1 λ λ

99 86 5 Application Tests of the Upconversion Technology λ = 635 λ = 1064 λ 2 = µ µ Theoretical considerations η = P 635 8d 2 = π2 P 1064 P 1572 cn 1064 n 635 n 1572 λ ϵ 0A L2 2 ( kl 2 ( kl 2 ) ) 2

100 5.2 Upconversion-based Long-range CO 2 DIAL Measurements 87 3 km CO2 FOV 2 Transmitter FOV 2 FOV 1 f=2000 mm r=100 mm 4f-beam scaling f=40 mm PPLN 0.2 mm FOV 1 Receiver d P i c n i λ 1572 ɛ 0 A L k k =0 Λ k = k 1064 k 635 [ ( k1572 k 635 )] (θ) k i = 2π λ i n(λ i,t) + k 1572 (θ)+ 2π Λ θ η η.. η η = η η η.. η η QE = π 0 η (θ) λ 635 λ 1572 Γ(θ)2πθ θ

101 88 5 Application Tests of the Upconversion Technology where Γ(θ) is the angular distribution of the incoming power. Together with the conservation of etendue, Eqs. (5.5)-(5.6) form the basis for the optimization of an upconversion based receiver system. With a 20 mm long PPLN crystal and a pump beam with a diameter of 100 µm, the full width half maximum (FWHM) of the external acceptance angle for the upconversion process is 1.8. The small acceptance angle together with the small overlap area in the crystal will constrain the design of the rest of the long range detection system and complicate a direct replacement of the InGaAs detector with the upconversion detector. A larger overlap area in the crystal results in a lower conversion efficiency for the collinear part as given by Eqs. (5.3) and (5.4). This can be compensated by a longer crystal, but at the expense of a lower angular acceptance bandwidth. It is, however, possible to find a compromise between the etendue and the QE that justifies the shift of wavelength to the visible regime and this will be discussed in further details in section Experimental Details The upconversion detector system is tested using the airborne demonstrator for the French/German MERLIN mission [90] developed at DLR. For the experiments described in the following, the upconversion detection system was set-up side by side to this lidar instrument to allow for a comparison between the direct detection (using InGaAs PIN diodes) and the upconversion approach. An overview of the transmitter and receiver of the airborne demonstrator is found in Fig. 5.5 together with the realization of the upconversion based test receiver setup. The MERLIN demonstrator is based on two optical parametric oscilladata Acquisition System Control Telescopes PIN UCD+PMT CO2 System (1572 nm) Energy Calibration OPO Pump Laser Frequency Stabilization 2 Seed Lasers PMT BP Filters PPLNcrystal 40 mm LD λ/2 Upconversion module Plate 200 mm 200 mm 40 mm Fiber Switch Seed Laser Figure 5.5: Left: Experimental details of the lidar transmitter system with the original receiver system side by side with the upconversion test setup. All IPDA measurements were controlled by the common data acquisition system. Right: Image of the upconversion detection system with diagram overlay. NIR signal Scaling and guiding Intracavity upconversion Visible PMT. tors (OPOs) which are diode-pumped by means of injection seeded, Q-switched Nd:YAG lasers in a master-oscillator power-amplifier configuration. Originally, the system generates radiation at both 1572 nm and 1645 nm, dedicated to CO2 and methane, respectively. In the context of this work only the CO2 part was employed. The IPDA technique requires the generation of two wavelengths

102 5.2 Upconversion-based Long-range CO 2 DIAL Measurements 89 µ µ ± > w = 100 µ w : 4 = 280 µ 4 µ µ µ

103 90 5 Application Tests of the Upconversion Technology Results and Discussion Atmospheric CO 2 Measurements

104 5.2 Upconversion-based Long-range CO 2 DIAL Measurements Noise Contributions < Angle Dependency 2 > <

105 92 5 Application Tests of the Upconversion Technology

106 5.2 Upconversion-based Long-range CO 2 DIAL Measurements 93 µ µ 2 ±110 Intensity=[mV] Thermal=gradient=crystal=heater Standard=crystal=heater 20 mm Temperature=[ C] Position=[mm] 1 a) b) Quantum=efficiency 0h8 0h6 0h4 0h2 No=gradient w 0 =50=µmV=P=50W No=gradient w 0 =100=µmV=P=50=W 9 C=linear=gradient w 0 =100=µmV=P=50W 5 C=linear=gradient w 0 =100=µmV=P=200W Distance=[m] 0 T40 T Acceptance=angle=[mrad]

107 94 5 Application Tests of the Upconversion Technology Future Improvements 2 a) b) c) Acceptance angle, FWHM [mrad] Absolute chirp [nm] No gradient, collinear phasematch 50 No gradient, collinear phasematch T [ C] Average quantum efficiency T [ C] Quantum efficiency External angle [mrad] Weighted quantum efficiency FWHM=125 mrad FWHM=190 mrad FWHM=250 mrad T [ C] 2

108 5.2 Upconversion-based Long-range CO 2 DIAL Measurements Conclusion 2

109 96 5 Application Tests of the Upconversion Technology 5.3 Summarizing Discussion µ µ 10 4 RDC=12%, Λ=11.8µm RDC= 6%, Λ=22.0µm 10 3 Photons [s -1 ] λ VIS [nm] 2

110 5.3 Summarizing Discussion nd -generation Upconversion Unit for Long Range Detection 2

111 98 5 Application Tests of the Upconversion Technology < 300 µ 4 4 w 0 = 200 µ 2

112 5.3 Summarizing Discussion 99 2 µ

113 100 5 Application Tests of the Upconversion Technology Quantum efficiency nd gen., 3.5 C gradient 2 nd gen., no gradient Acceptance angle [mrad]

114 5.3 Summarizing Discussion 101 µ

115 102 5 Application Tests of the Upconversion Technology PMT or APD µ

116 CHAPTER 6 Outlook and Conclusion 6.1 Outlook 2 µ µ

117 104 6 Outlook and Conclusion 6.2 Conclusion 2

118 6.2 Conclusion 105

119 106

120 APPENDIX A List of Abbreviations

121 108

122 APPENDIX B Overview of Poling Periods and Datasheet Example µ µ µ

123 110

124 APPENDIX C Intarsia Cavity Design Example

125 112

126 APPENDIX D Aligment Procedure - Parametric Module Cavity > 300 µ 00

127 114

128 APPENDIX E Poster Presented at ASSL Paris 2013 Optical Sensor Technology Group Mid-infrared seeded optical parametric amplified light source Lasse Høgstedt*, Peter Tidemand-Lichtenberg, Christian Pedersen Technical University of Denmark, lhog@fotonik.dtu.dk Abstract Introduction We present a two stage pulsed midinfrared light source based on nonlinear down-conversion of light. The light source is single frequency, tunable, all passive and single moded. Three configurations are presented: Spontaneous parametric fluorescense (un-seeded) Near infrared (NIR) seed Mid-infrared (MIR) seed A single frequency, tunable and pulsed light source is needed to construct a successful system for remote gas detection. This could be deployed in a differential absorption LIDAR (DIAL) system. Previous work, [1-3] on seeded OPA's have primarily focused on seeding at the NIR wavelength in the DFG process, whereas this project presents the results from MIR seeding. The output wavelengths are defined from the energy and momentum conservation in the difference frequency generation in the OPA where λ s is the generated mid-ir light, λ p the passive Q-switched laser, λ id the residual energy from the pump photon and the k's is the corresponding wave numbers. Average power [mw] Idler at 1598 nm Signal at 3190 nm 200 Pump at 1064 nm Crystal length [mm] A simulated example of the average power evolution through an OPA crystal, seeded at the MIR wavelength Setup The all passive setup consists of four main parts: An OPA, two seeds and an OPA pump. The mid-ir seed is a single frequency, tunable CW lightsource based on DFG mixing between a tunable 1 W 800 nm laser and a 1064 nm intracavity field. [4] Tunable laser at 1598 nm 1064 nm Q-switched laser Tunable laser at 800 nm 1598 nm NIR-seed OPA 1064 nm OPA pump 3190 nm MIR-seed Intensity [dbm] NIR-seed Wavelength [nm] 30 OPA pump Intensity [dbm] 35 Output 1: 40 With NIR-seed Wavelength [nm] For the NIR seed a tunable Ando AQ4321D is used. The OPA pump is a passive Q-switched laser build with Nd/Cr:YAG-crystals [5]. The pulse width is 7 ns, the repetition rate 5 KHz and the pulse energy 75 μj In the final stage all beams overlap in a 40 mm long temperature controlled 5 % MgO doped PPLN crystal. Intensity [dbm] Intracavity DFG Conceptual drawing of the setup. It is possible to switch between the two different seeds. Output has always all three components as a result of the DFG process. The panels to the right display measurements of the different spectra. 45 Tunable 60 Intra cavity 50 laser pump Intensity [dbm] Intensity [dbm] Intensity [dbm] Wavelength [nm] 100 Calculated 105 MIR seed Intensity [dbm] Intensity [dbm] Wavelength [nm] Output 3: 40 With MIR-seed Wavelength [nm] Wavelength [nm] Wavelength [nm] Wavelength [nm] Results If the OPA is seeded and measured at the same wavelength the spectral output will reflect the width of the seed, whereas it will represent the width of the OPA pump if the seed is shifted to the other wavelength. At the MIR wavelength the peak width is calculated to shift the FWHM from ~2 nm with the NIR seed to 0.1 nm with the MIR seed. To the right is an example of the MIR output where the NIR-case is the convolution between the OPA pump and the NIR-seed, and the MIRcase represents an amplification of the calculated MIR seed. The power levels give a feeling of the different conversion efficiencies. All the intensities on the spectra have an arbitrary reference level. Intensity [dbm] OPA pump 1064 nm OPA pump only 1598 nm NIR seed only MIR seed only OPA pump only 3190 nm With NIR seed With MIR seed Average power [mw] Calculated MIR output Output with NIR seed Output with MIR seed Wavelength [nm] { { { Conclusion We have demonstrated a tunable, pulsed mid-ir light source based on parametric downconversion of light. The results show that the spectral width of the output decreases significantly when we seed directly at the mid-ir wavelength. The system proofs a general method to produce high quality mid-ir pulses with an all passive system over a wide range of frequencies Outlook A measurement of the mid-ir spectrum directly with a monochromator and investigate the pulse to pulse stability. Apply the light source for remote gas sensing. References: 1) P.E. Powers, K.W. Aniolek, T.J. Kulp, B.A. Richman, and S. E. Bisson, Opt. Lett., 23,1886 (1998) 2) T.J. Kulp, S.E. Bisson, R.P. Bambha, T.A. Reichardt, U.-B. Goers, K.W. Aniolek, D.A.V. Kliner, A.A. Richman, K.M. Armstrong, R. Sommers, R. Schmitt, P.E. Powers, O. Levi, T. Pinguet, M. Fejer, J.P. Koplow, L. Goldberg, T.G. Mcrae, Appl. Phys. B 75, (2002) 3) A. R. Pandey, P. E. Powers, and J. W. Haus, IEEE J. Quantum Electron, 44, 203 (2008) 4) L. Høgstedt, O. B. Jensen, J. S. Dam, C. Pedersen, P. Tidemand-Lichtenberg, Laser Physics, 22, 1676 (2012) 5) P.T. Lichtenberg, M. T. Andersen, S. Johansson, C. Canalias, F. Laurell, P. Buchhave, E. Karamehmedovic, C. Pedersen, Opt. Expr. 15, 9799 (2007)

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130 APPENDIX F Poster Presented at ASSL Berlin 2015 Lasse Høgstedt*, Peter Tidemand-Lichtenberg, Christian Pedersen Technical University of Denmark, lhog@fotonik.dtu.dk Optical Sensor Technology Group Design of a solid state laser for low noise upconversion detection Few photon infrared signal Few photon infrared signal InGaAs - detector Low QE, high noise Abstract Introduction We present an analysis of a solid state mixing laser used for upconversion of infrared to visible light. It is demonstrated how to optimize the upconversion process for maximum signalto-noise ratio, when used in a detector system. It is found that the mixing laser intensity should be 300 KW/cm 2 in the system example. Few photon infrared signal Detectors in the near infrared region are used for spectroscopic gas detection, e.g. CO 2 in the atmosphere at 1572 nm [1]. An InGaAs semiconductor detector is the typical choice, but the quantum efficiency (QE) is low and the dark noise high at room temperature. If the wavelength of the signal is converted to the visible region it is possible to detect the light using highly efficient low noise silicon detectors [2,3]. The conversion results from the addition of energy in a nonlinear sum frequency generation (SFG) process with an efficiency defined as One of the main challenges with efficient signal upconversion is the noise from spontanous parametric downconversion (SPDC) [4]. The problem is enhanced by random poling errors in the nonlinear crystal, that induce a non-zero phasematch at all wavelengths [5]. The SPDC is upconverted to the signal wavelength and the phasesmatch for the combined process is illustrated below. k nm k nm φ 1 θ 2 φ 2 k nm k nm θ 1 k nm Δk SPDC=k 2+k 3-k 1+k qpm and Δk SFG=k 1+k 3-k 4+k qpm, where k(t, λ) Setup The upconversion module consist of a 1064 nm high finesse laser cavity with a periodically poled lithium niobate crystal placed intracavity. Three points for efficient upconversion are emphasized: A compact and robust design ensure stability and easy in- and output coupling. A small beamwaist inside the nonlinear crystal and a finesse>400 ensure a high intensity mixing field. The nonlinear crystal is placed inside an oven on a translation stage. This allows for tuning of the specific phasematch by temperature tuning and/or shifting between the five poling channels. Laser diode 3 W 880 nm Calibrated leak 1 cm 100 mm f=50 mm ND:YVO nm 20 mm Mg:PPLN 30 mm L=11.8 mm T=131 C w0=48 mm 75 W intracavity power Upconversion module Sketch of the solid state laser that defines the upconversion module. All mirrors have losses below 0.02% at 1064 nm. Image of the realization of the upconversion module. Few photon visible signal Visible noise photons Intensity [a.u.] Noise There exist five different noise sources in the upconversion process, all visible on the plot below, displaying the output with no signal in. Upconverted SPDC noise, enters both as a peak at the signal wavelength and as a pedestal around. Cannot be filtered away. Thermal noise, essentially at all wavelengths. Low in NIR region. Typically not phasematched. Mostly filtered away. Raman noise, higher order phasematching and laser diode residual. All three typically not at the signal wavelegnth. Can be filtered away Wavelength [nm] Signal-to-noise ratio Dark noise Upconversion efficiency Signal-to-noise ratio Intensity [MW/cm 2 ] Intensity [MW/cm 2 ] Intensity [MW/cm 2 ] The dominant noise source in the At low intensities the efficiency of With a quadratic dependency for the upconversion process after narrowband filtering is upconverted SPDC. At higher efficiencies the signal saturates at high intensities there is the upconversion process is linear. dominant noise source and a QE that depletes and the intensity an optimum for the SNR of the It depends quadratically on the dependency become sinusoidal. upconversion process. mixing field intensity as the efficiency for both processes depend QE>80% have been demonstrated From the plot the optimum for the linearly on this intensity. with this system. specific system is I 1064=300 KW/cm 2. References: 1) 2) 3) 4) 5) 6) Zero signal noise [pw] Quantum efficiency [norm.] Ehret, G., Kiemle, C., Wirth, M., Amediek, A., Fix, A., Houweling, S. "Space-borne remote sensing of CO 2, CH 4, and N 2O by integrated path differential absorption lidar: a sensitivity analysis", Applied Physics B, 90, (2008) L. Høgstedt, J. S. Dam, A. Sahlberg, Z. Li, M. Aldén, C. Pedersen, and P. Tidemand-Lichtenberg, "Low-noise mid-ir upconversion detector for improved IR-degenerate four-wave mixing gas sensing", Optic Letters 39 (2014). T. Wong, J. Yu, Y. Bai, W. Johnson, S. Chen, M. Petros, and U. N. Singh, ``Sensitive infrared signal detection by upconversion technique,'' Optical Engineering 53, (2014). C.L. Tang, "Spontaneous Emission in the Frequency Up-Conversion Process in Nonlinear Optics", Physical Review 182, (1969). J. S. Pelc, C. R. Phillips, D. Chang, C. Langrock and M. M. Fejer, Efficiency pedestal in quasi-phase-matching devices with random duty-cycle errors, Optic Letters 36, (2011) L. Høgstedt, M. Wirth, C. Pedersen, and P. Tidemand-Lichtenberg, "Upconversion based long range CO 2 DIAL measurements" - to be submitted Signal to noise ratio Few photon visible signal Visible noise photons Conclusion We have demonstrated a high finesse solid state laser module optimized for upconversion of infrared light to visible light. The analysis show how upconverted SPDC noise dominate and that an optimum SNR is reached with I 1064=300 KW/cm 2. Outlook This general optimization approach for upconversion detection can be applied for longer wavelength detection systems with different poling periods. The system performance should be tested against state-of-art NIR detection systems [6]. Silicon - detector High QE, low noise

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132 APPENDIX G Selected Noise Spectra of the Upconversion Process Intensity [counts] Poling period [µm] Wavelength [nm] µ µ µ µ Intensity [counts] µm 9.3 mw 37.2 C No poling µm 3.2 mw C µm 21.2 mw 45.9 C 23.0 µm 19.7 mw 45.9 C Wavelength [nm]

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134 APPENDIX H Statistical Data for Poling Period Measurements µ µ Λ = 11.8µ Λ = 22.0µ

135 122 H Statistical Data for Poling Period Measurements Λ = 22.0µ

136 APPENDIX I Model Comparison with Identical Random Gratings 10 4 SBS-model FFT-model Photons [s -1 ] λ VIS [nm] µ

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138 Pixel selection A Pixel selection B Pixel selection C Pump 1 Probe Pump 3' Signal 4' 2' 1' APPENDIX J Poster Presented at Photonics West 2014 Optical Sensor Technology Group Upconversion enhanced degenerate four-wave mixing in the mid-infrared for sensitive detection of acetylene in gas flows Lasse Høgstedt a, Jeppe Seidelin Dam* a, Anna-Lena Sahlberg b, Zhongshan Li b, Marcus Aldén b, Christian Pedersen a, Peter Tidemand-Lichtenberg a a Technical University of Denmark, Dept. of Photonics Engineering, Frederiksborgvej 399, 4000 Roskilde, Denmark b Lund University, Dept. of Physics, Combustion Physics, Professorsgatan 1, SE Lund, Sweden Abstract We present a new background free method for in situ gas detection. A combination of degenerate fourwave mixing and an infra-red light detector based on parametric frequency upconversion. It is demonstrated that the system is able to cover more than 100 nm in scanning range and detect concentrations below 1 ppm based on the R9e acetylene line. Mid-IR source Upconversion = + λ VIS λ MIR λpump Detector Degenerate Four-Wave Mixing Cooled InSb Detector Above: Conceptual overview of the setup, see details in the bottom. To the right: Direct comparison between the noise levels for the upconversion detector and the InSb detector. Intensity [a.u.] 10 6 Line integrated IR DFWM signal intensities ax 2 Cooled InSb detector noise level ppm x Upconversion detector noise level 0.5 ppm Acetylene concentration [ppm] Data analysis From data to spectrum with the upconversion detector: Acquire one image per pulse Subtract background Define the pixel selection area Sum the pixels in each frame Construct a spectrum from all frames Three examples of scattering influence are displayed in figure 3. B A C Normalized intensity Wavenumber [cm -1 ] Data from three different pixel selections in images from the upconversion detector. B simulates a case without pixel selection, A and B demonstrates the best and worst case scenario respectively. Measured at an acetylene concentration of 11 ppm. Results From scans with the two detectors it was possible to demonstrate close to a 500 times improvement in detector noise level. This was both due to spatial filtering of the scattering and the inherent lower noise levels in the visible light detector. The spectra below show examples of spectra obtained with the two different detectors. The wide scan show how it was possible to cover a broad spectral region with a high dynamic range. The detection levels are limited by scattering in the system and the lower limit of the flow controller. Intensity [a.u.] Upconversion detector, 12 ppm C2H Measurement data Reference spectrum Wavenumber [cm 1 ] Upconversion detector InSb detector Intensity [a.u.] 12 ppm C H 2 18 ppm C 2 H 2 27 ppm C H Wavenumber [cm -1 ] First: Broad scan over the acetylene spectrum together with a simulation based on the HITRAN2008 database. Second and third: Scan over the R9e acetylene line for various concentrations with the upconversion detector and the InSb detector respectively. Both are an average of 10 scans and all have running average on 20 points. Intensity [a.u.] ppm C 2 H ppm C 2 H ppm C 2 H ppm C H 2 Ref. norm. to 3 ppm Wavenumber [cm -1 ] WWavenumber [] Description of experiment The mid-infrared light is generated by a tunable DFG system [1] and split into four beams using the specially designed IR-BOXCAR plates [2]. Three of these beams are focused into the middle of the gas tube. The signal beam is collimated and directed to the detectors. The upconversion detector [3] consists of two parts, a conversion unit and a CCD based camera. In the conversion unit the mid-infrared light is focused into a 20 mm long periodically poled 5% MgO doped lithium niobate crystal. Here it is mixed with a intra-cavity field of a 1064 nm laser in order to generate light at the sumfrequency around 800 nm. This is defined from the conservation of both energy and momentum. Gas Tube Mid-IR M laser WP T W PM M HeNe A DM L BP M OS D A L C2H2+ N2 A L A Upconversion Detector GT M DM PP:LN DM A FM A MIR VIS M DM Pump PL UD LC M: mirror, WP: waveplate, T: telescope, W: CaF window, DM: dichroic mirror, A: aperture, BP:BOXCAR plates, L: lens,gt: gas tube, D:InSb photoconductive detector, OS: oscilloscope, FM:flip mirror, UD: upconversion detector system PL: Pump laser, LC: Laser Crystal, VIS: CCD camera, PP:LN: Nonlinear upconversion crystal Conclusion We have demonstrated gas sensing with a DFWM system combined with an upconversion detector for the mid-ir region. Results show sub-ppm acetylene detection levels and a noise level improvement of approx. 500 times compared to a cryogenically cooled InSb detector. The imaging capabilities of the upconversion detector allows spatial filtering of the system scattering, in order to lower the main noise source. References: 1] Li, Z. S., Hu, C. H., Zetterberg, J., Linvin, M., Alden, M., Midinfrared polarization spectroscopy of OH and hot water in low pressure lean premixed flames, Journal of Chemical Physics 127, (2007) [2] Sun, Z. W., Li, Z. S., Li, B., Alden, M., Ewart, P., Detection of C2H2 and HCl using mid-infrared degenerate four-wave mixing with stable beam alignment: towards practical in situ sensing of trace molecular species, Applied Physics B: Lasers and Optics 98, (2010) [3] Dam, J. S., Tidemand-Lichtenberg, P., and Pedersen, C., Room-temperature mid-infrared single-photon spectral imaging, Nature Photonics 6, (2012)

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