Ultrafast Wavelength Tuning and Scaling Properties of a Noncollinear Optical Parametric Oscillator (NOPO) Thomas Binhammer 1, Yuliya Khanukaeva 2, Alexander Pape 1, Oliver Prochnow 1, Jan Ahrens 1, Andreas Wienke 1, Tino Lang 3 and Uwe Morgner 2 1 Laser Quantum, Hannover, Germany 2 Institut für Quantenoptik, Universität Hannover, Germany 3 Deutsches Elektronen-Synchrotron DESY, Germany
Motivation Spectroscopy: Stimulated Raman Scattering Detection and analysis of microplastics in the water Microscopy: Multiphoton Fluorescence Microscopy Excitation of fluorophores at two different wavelength with very fast switching 1 Lisbeth Van Cauwenberghe et al., EP, V182, P. 495 499 (2013) 2 Rueck, JBO 19(9), 096005 (2014)
Concept and Setup Yb-based fiber oscillator / amplifier @1 µm High average output power and repetition rate Ultrashort, intense pump pulses Scalable! Second harmonic generation Noncollinear Optical Parametric Oscillator (NOPO) Fast ultrawide tunability Ultrabroad spectral range 650-950 nm High average power, repetition rate Pump Laser SHG generation Noncollinear OPO lang@iqo.unihannover.de
Parametric amplification Energy conservation: ω p ω s p = 532 nm s = 800 nm SHG ω i i = 1588 nm Idler Signal Tangential phase matching Poynting vector walk-off compensation
Basic Idea Positive intra-cavity dispersion acts as spectral filter in time domain Only spectral components arriving simultaneously with pump pulse are amplified Center wavelength and bandwidth selected by chirp and cavity detuning
Experimental Setup Non-collinear Optical Parametric Oscillator (NOPO)* - Ultrabroadband phase matching and gain due to non-collinear geometry - Stable ML operation by introducing positive net dispersion in resonator * Patent number US13/642,618; EP11 715 664.6
Basic Idea Cavity detuning by dispersion With 96 mm fused silica per roundtrip, a detuning of 500 µm is required for full tuning range
Experimental Results Spectra tuning curves and output power Ultrawide tuning from 630 to 1070 nm by only changing cavity length Power drop around 920 nm due to parasitic SHG in PVWC geometry
Stability I Free running NOPO: Stable output power with low rms noise of 0.5% (1h) Slight wavelength drift due to absence of stabilization between fiber oscillator and NOPO cavity
Stability II Actively stabilized NOPO: Wavelength control with piezo actuator and motorized stage Piezo-controlled end mirror for power optimization
Tuning speed Due to broadband phase matching, tuning speed is only limited by mechanical movement. - Ultrafast sweeping of NOPO demonstrated with > 100 nm/ms -New piezo actuator can be used for ultrafast scanning or wavelength selection / switching (in progress)
How fast can we get? Calculated cavity life time < 200 ns High speed switching can be done very fast (rotating glass plate) Detection by two photodiodes in Fourier plane of 2-f setup Nopo wavelength is changed within < 200 µs over 100 nm Corresponds to a speed of more than 500 nm/ms Fastest switching speed from a broadband fs source
Upgrade of pump laser for NOPO: Fiber oscillator and amplifier > 80 W @ 1040 nm, f rep = 50 MHz Scaling potential
Scaling potential + Pump intensity can be kept at right level by adapting focussing + No thermal issues expected due to parametric gain Fiber oscillator and amplifier > 80 W @ 1040 nm, f rep = 50 MHz - Mode matching with cavity focus - Thermal issues in cavity mirror Scaling of pump power
Scaling potential + Pump intensity can be kept at right level by adapting focussing + No thermal issues expected due to parametric gain Fiber oscillator and amplifier > 80 W @ 1040 nm, f rep = 50 MHz - Mode matching with cavity focus - Thermal issues in cavity mirror Scaling of pump power Scaling of parametric oscillator (coll.)
Tuning of NOPO PVWC PM: + low signal walk-off + NOPO bandwidth easy to achieve - SHG dip Idler SHG Signal Tangential PM: + no SHG dip - strong signal walk-off - larger focus required for NOPO Tangential phase matching Poynting vector walk-off compensation
Comparison of geometries Poynting vector walk-off compensation Tangential phase matching
Comparison of geometries Poynting vector walk-off compensation Tangential phase matching
Comparison of geometries Poynting vector walk-off compensation Tangential phase matching
Comparison of geometries Poynting vector walk-off compensation Tangential phase matching
Comparison of geometries Poynting vector walk-off compensation Tangential phase matching
Summary Results High power output > 3 W, 60 nj (50 MHz) over wide spectral bandwidth Tunable from 650 nm 1200 nm by only detuning resonator length Sweeping frequency limited by speed of mechanical movement Ultrafast switching between two wavelength within less than 200 > 500 nm / ms tuning is possible with NOPO Both geometries are feasible for NOPO operation Outlook: Usage of full SHG power with adaption of cavity Change to ring cavity Implementation of nonlinear intra-cavity conversion processes (PO-1,5) Temporal and spatial simulation of NOPO dynamics
Thank You! Achknowledgement: This wors supported by. Spektral sensitive Mikroskopie mittels excitation fingerprinting basierend auf einem nichtkollinear optischparametrischen Oszillator Contact: Thomas Binhammer tbinhammer@laserquantum.com
IR-NOPO Tuning I Output power of NOPO while tuning black: PVWC geometry blue: Tangential geometry Typical NOPO spectrum Fourier-limited pulse duration
Experimental Results Signal Output Power and Stability Power slope Long term stability
Experimental Results Signal Output Power and Stability Power slope Long Autocorrelation term stability