1. 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

2. 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

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

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

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

6. 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

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

8. 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

9. 3% pk to pk power stability over 24 hours
Sdev 0.6%
Power stability plot

10. 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

11. 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

12. 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

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

14. Photoacoustic spectra with 16kHz frequency modulation using DBR diode seed

15. Beam profile – close to diffraction limit
Beam quality measurement

16. 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

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

18. 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