Ultrafast Optical Parametric Oscillators


The ultrafast optical parametric oscillator group carries out research on both the development of these coherent light sources and their applications.

Optical parametric oscillators (OPOs) perform very much like standard laser sources, with an optical gain medium and an optical resonator.  However, in this case the gain medium is not based, for example, on atomic transitions, but instead on parametric frequency conversion in a nonlinear crystal. Modern nonlinear crystals, such as  periodically-poled LiNbO3 (PPLN), offer designer microstructures that can be used to phase-match a particular nonlinear interaction.  OPOs therefore offer some unusual and highly advantageous properties such as:

1. Broad wavelength tunability, much greater than the standard solid-state laser option – the Ti:sapphire laser.

2. Access to important wavelength regions, such as the mid-IR.

3. No heat input into the crystal from the basic gain process, in contrast to even the most efficient rare-earth-ions, such as Yb3+, thereby offering potential for power scaling.

4. A variety of output formats - continuous wave, pulsed, or ultrafast, depending upon the pump laser.

Our research aims to explore such possibilities and find new applications for these extraordinary devices. 

Key research breakthroughs:

The use of fibre-amplified gain-switched diode lasers as OPO pump sources for compact, efficient, power and energy scalable ultrafast devices with repetition rates from 10MHz to 10GHz
F.Kienle et al, Optics Express 18 (2010) 7602-7610
F.Kienle et al, Opt. Lett. 35 (2010) 3580-3582

Adaptively shaped ultrafast mid-IR pulses from an OPO with applications in coherent control
J.Prawiharjo et al, Optics Express 16 (2008) 15074-15089; F.He et al, Optics Express 16 (2008) 5813-5821; H.S.S.Hung et al, J. Opt. Soc. Am B (2007) 2988-3006; J.Prawiharjo et al, J. Opt. Soc Am B (2007) 2484-2493; J.Prawiharjo et al, J. Opt. Soc. Am B (2007) 895-905; N.Naz et al, Opt. Express 13 (2005) 8400-8405

OPOs with output beyond 5µm

M.A.Watson et al, Opt. Lett. 28 (2003) 1957-1959; M.A.Watson et al, Opt. Lett. 27 (2002) 2106-2108

Fibre-laser-pumped OPOs for compact, efficient, power-scalable devices
M.V.O’Connor et al, Opt. Lett. 27 (2002) 1052-1054

The use of diffraction gratings and birefringent filters for convenient, fast wavelength tuning and stable operation close to degeneracy
M.V.O’Connor et al,  Appl. Phys. B (2004) 15-23; D.C.Hanna et al, J. Phys. D: Appl. Phys. 34 (2001) 2440-2454

Impact of research:

To date the major impact of our ultrafast OPO work has been felt in the academic arena through dissemination of our results in high-impact-factor journals, such as those mentioned above, and at major international conferences.  However, we have also been long-term collaborators with Covesion Ltd, a local spin-out company, who have successfully commercialised work at the ORC on periodic poling of LiNbO3.  We continue to work with Covesion Ltd on our ultrafast OPO development and they offer an ideal route to knowledge transfer and potential commercialisation of these devices.

With the growing use of compact and efficient, power-scalable, fibre-laser pump sources, ultrafast OPOs will find growing use beyond laboratory-based scientific applications.  Therefore the emphasis of our work is now shifting to applications of OPO devices and this has led us to collaborative discussions with medical scientists for applications such as nonlinear microscopy, with academics and industrialists interested in materials processing for applications such as pulsed-laser-ablation and deposition of polymer thin films, and with industrialists in the defence arena. 

Research facilities:

Our research group benefits from two large well-equipped labs dedicated to ultrafast OPO research.  We also carry out research in collaboration with other groups, especially the ultrafast fibre laser group of Prof. David Richardson, and thereby benefit from access to their laboratories as well.  We are also uniquely well-placed to benefit from fabrication of advanced periodically-poled nonlinear crystals from Covesion Ltd and novel optical fibres produced in the ORC’s world-leading fabrication facilities for specialist fibre-laser pump sources.

Current research projects:

Power-Scaled Optical Parametric Oscillators
In collaboration with Prof. David Richardson (ORC) and Covesion Ltd.
The current theme of our research lies in exploiting the recent advances in fibre pump laser technology to further enhance the output properties of OPOs. This includes average-power scaling of both picosecond and femtosecond OPOs through the use of power-scaled fibre laser sources, highly compact GHz-repetition-rate OPO systems based on fibre-amplified gain-switched diode pump lasers, and MHz-repetition-rate, high-pulse-energy OPOs using long but compact fibre-feedback cavities.

Table-Top Lasers for Resonant Infrared Deposition of Polymer Films
In collaboration with Prof. David Richardson (ORC) and Covesion Ltd.
In this proposal we will build a novel, compact and efficient source of high-energy (µJ), picosecond pulses with broad tunability in the mid-IR (1.3 to 5µm).   The source is based on a synchronously pumped optical parametric oscillator with a fibre feedback arm to conveniently allow long cavity lengths, relatively low repetition rates, and hence high pulse energies suitable for pulsed laser ablation and deposition.  It will be pumped by a simple gain switched diode laser, scaled to high average powers by an Yb-doped fibre amplifier.  This unique source will then be used to demonstrate the deposition of high-quality, chemically unmodified, polymer thin films of high technological importance.  This will be done by using the resonant infrared pulsed laser deposition (RIR-PLD) technique, which to date has largely relied on the use of free electron lasers.  The controllable repetition rate and the opportunity to exploit the nonlinear spectral broadening within the fibre amplifier will allow a comprehensive study of the pulse energy, repetition rate, and pulse duration parameter space, to fully optimise the RIR-PLD process.  We believe the development of this source and its demonstrated implementation for polymer deposition will have a high impact in numerous technological areas covering photonics, electronics, microelectromechanical systems (MEMS), and medicine.  This project is supported by EPSRC grant EP/I02798X/1.

Past research projects:

An Intelligent Mid-Infrared Pulse Generator for Experiments in Coherent Control
In collaboration with Prof. David Richardson (ORC) and Prof Jeremy Frey (Chemistry)
EPSRC EP/C009479/1 and GR/T25590/01
Coherent control of quantum phenomena offers exciting opportunities to physicists, chemists and biologists for the manipulation of solid-state and molecular systems by using specially shaped ultrashort laser pulses to excite the system. Theoretical design of optimal pulse shapes for molecular excitation is possible for only the simplest of molecular systems. So an emerging technique involves the exploitation of optimal control theory to achieve an optimal pulse shape, by using the experimental output as feedback to the optimization process. In this way, the molecule itself is used as an analogue computer to solve its own equations of motion in real-time. The instrument developed in this proposal was an intelligent mid-IR pulse generator capable of optimally exciting specific local molecular vibrations. We exploited the fact that high-fidelity, pulse-shaping schemes exist for wavelengths ranging from the visible to the near-IR, and used this to control the shape of pulses at longer wavelengths via parametric frequency conversion. This was accomplished by high-fidelity transfer of pulse shapes from the near-IR pump to the mid-IR idler of a synchronously pumped OPO. In addition, we implemented ‘closed-loop’, adaptive control of the idler pulse shape using a learning algorithm.  This instrument was based on a power-scalable, femtosecond fibre pump laser.

Synchronously-Pumped Optical Parametric Oscillators: Basic Studies and Performance Enhancement
EPSRC GR/R01224/01
This proposal aimed to increase the versatility of synch-pumped OPOs and develop a better understanding of the physical basis for their operating characteristics, in order to enhance their utility for numerous potential applications. The work was based on periodically-poled lithium niobate (PPLN) and investigated high pump powers to access (1) wider tuning ranges, (2) simultaneous operation of two independently tuneable OPOs for pump-probe applications (3) operation of tandem OPO schemes, in which one OPO pumps another, thus accessing longer wavelengths, shorter pulse durations.

Collaborations:

Internal: We collaborate strongly with the ultrafast fibre laser group of Prof. David Richardson within the ORC and actively seek engagement with other groups in the University of Southampton to find applications such as coherent control (with Chemistry), nonlinear microscopy (with Medicine), and materials processing (with Prof. Rob Eason, ORC).

Academic: We are currently discussing projects with collaborative academic partners in the UK, Europe and the USA concerning the use of fibre-laser-pumped OPOs for a number of applications.

Industry: We are long-term collaborators with Covesion Ltd, who fabricate high-quality periodically-poled nonlinear crystals and are in discussion with industrial partners in the UK and the USA over various applications of ultrafast OPO systems.

Work with us:

We are always open to collaborative projects, please contact Professor David Shepherd for more details.

PhD projects with this group:

We are currently seeking PhD students to work in the area of power and energy scaling of fibre-laser-pumped ultrafast OPOs and their applications in areas as diverse as bio-imaging and materials processing.  

Copyright University of Southampton 2006