Optical Parametric Oscillators

The Optical Parametric Oscillators group is led by Professor David Shepherd. The potential of optical parametric oscillators (OPOs) as versatile tools for an extensive range of applications is widely appreciated. The arrival of new nonlinear materials, which are structured so as to have a periodic variation in non-linearity, have had a dramatic effect on nonlinear optical devices.

The work in this group draws on the world leading fabrication capabilities for these materials at the ORC (eg periodically-poled lithium niobate, PPLN, PPKTP, PPRTA) and explores the exciting new device possibilities. These include optical harmonic generators, optical parametric oscillators and amplifiers.

The group is currently involved in the main project areas described below, but we also collaborate frequently on related projects with other research groups, both within the ORC and externally. Our research is predominantly funded through EPSRC grants.

An Intelligent Mid-Infrared Pulse Generator for Experiments in Coherent Control

We have significant EPSRC funding to investigate the development of an intelligent mid-IR pulse generator for experiments in coherent control. This work is in collaboration with Prof. David Richardson of the ORC and Dr. Jeremy Frey of the School of Chemistry.

Coherent control (CC) of quantum phenomena offers exciting opportunities to physicists, chemists and biologists for the manipulation of solid-state and molecular systems by using 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 (OCT) to achieve an optimal pulse shape, by using the experimental output in 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 to be developed in this proposal is an intelligent MIR pulse generator capable of optimally exciting specific local molecular vibrations in order to drive large-scale collective motions of whole domains (conformational change). We will exploit the fact that high-fidelity, pulse-shaping schemes already exist for wavelengths ranging from the visible to the NIR, and will use this to control the shape of pulses at longer wavelengths via parametric frequency conversion. This will be accomplished by high-fidelity transfer of pulse shapes from the NIR pump to the MIR idler of a synchronously pumped optical parametric oscillator. In addition, we will implement ‘closed-loop’, adaptive control of the idler pulse shape using a learning algorithm for AOCC applications.

In order to deliver long-term value and wide future availability, this instrument will be based on a power-scalable, all-fibre, sub-100fs pump laser. This will enable high average powers (up to 100W) at high pulse repetition rates (50MHz) for low-noise and fast data acquisition, but with the flexibility to move to low repetition rates and higher pulse energies for various possible future application regimes.

• Synchronously pumped optical parametric oscillators
• Periodically poled LiNbO3
• Ultrashort pulse shaping and characterisation
• High-power shaped-pulse fibre lasers
• Parametric transfer of shaped pulses
• Adaptive control
• Applications of ultrashort pulses

Synchronously-Pumped Optical Parametric Oscillators: Basic Studies and Performance Enhancement

This proposal aimed to increase the versatility of synch-pumped optical parametric oscillators (SPOPOs) 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 built upon an existing SPOPO system, based on periodically-poled lithium niobate (PPLN), adding a power amplifier to boost the pump laser to a level that permits (1) wider tuning ranges to be accessed, (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 pulses durations.