Angus Henderson, Paul Hoffman and Ryan Stafford Multi-Watt Single Frequency Output from 1.4 to 4.2 Microns (2400 to 7100cm-1) from a Single Laser System Angus Henderson, Paul Hoffman and Ryan Stafford Aculight Corporation Bothell, WA 6/21/07 Title slide: 8.6 Watt single frequency CW OPO

Practical laser sources for spectroscopy scarce in 2 to 4mm region Lead salt lasers – low power, poor spectral quality, cryogenics DFG sources – low power Diode lasers – mostly below 2mm Quantum cascade lasers – not below 4mm

ArgosTM is a single frequency CW OPO pumped by a 15 Watt fiber laser OPO system configuration OPO configuration Control unit and OPO head

OPO produces two high power SLM outputs Signal 1660nm, idler 2950nm

Wavelength modules are interchangeable with same pump laser Power vs wavelength Signal wavelengths Idler wavelengths Wavelength modules are interchangeable with same pump laser

Short term linewidth < 60kHz (2*10-6 cm-1) Beat frequency measured between two OPOs tuned to 2930nm Timescale 500 microseconds Same measurement gives 600kHz linewidth over 80 ms OPO linewidth measurement

Dn < 30 MHz over 2 minutes Frequency stability measured by “parking” frequency on an N2O line at 2984nm Dn < 30 MHz over 2 minutes

Mode-hop-free operation over 14 hours 30pm variation in 14 hours – driven by temperature No mode hops once equilibrium temp. reached No active feedback or cavity temp. control 150MHz stability over 10 hours with cavity temp. control Wavelength drift

3% pk to pk power stability over 24 hours Sdev 0.6% Power stability plot

Coarse tuning ~700nm tuning via poling period OPO poled with fan-out pattern – period varies linearly across crystal OPO tunes by translating crystal relative to pump beam Temp tuning also allows coarse tuning Coarse tuning plot

Tuning by galvo rotation of intracavity etalon Intermediate tuning - Etalon tunes ~9nm through adjacent free spectral ranges Tuning by galvo rotation of intracavity etalon Etalon tuning plot

synchronously with pump Fine mode-hop-free tuning by temperature or PZT tuning of fiber seed laser DFB fiber laser is default seed Alternate seeds can be used e.g. DBR diode Fine tuning by pump tuning OPO idler tunes synchronously with pump

Fine tuning allows rapid spectral scans CO2 Data obtained in single sweep, 30ms Data matches theoretical calculations

Photoacoustic spectra with 16kHz frequency modulation using DBR diode seed

Beam profile – close to diffraction limit Beam quality measurement

Wavelength extension – sum frequency generation and second harmonic generation Intracavity signal power is 100s of Watts SFG (signal + pump) produces ~0.3mW 600 to 700 nm SHG (signal) produces >1mW 700 to 1000 nm SHG of idler produces 1000 to 1400nm All single frequency outputs

Future – CW OPO using OP-GaAs Collaboration with Stanford U. Can be pumped by Erbium or Thulium fiber laser Transparent out to 16 mm

Aculight CW OPO product Demo unit running at Aculight booth Conclusion: OPO is a robust, powerful source for near to mid-infrared spectroscopy Provides multi-Watt level power in both near-IR and mid-IR Single frequency output at signal and idler Mode hop free tuning of ~60GHz Near-diffraction-limited beam quality Stable in power and frequency Fiber laser provides robust pump source Aculight CW OPO product Conclusion – OPO is ideal source for mid-IR spectroscopy Demo unit running at Aculight booth