| EPSRC Reference: |
EP/F031688/1 |
| Title: |
InAs/GaAs quantum dot SESAMs for long wavelength applications |
| Principal Investigator: |
Murray, Professor R |
| Other Investigators: |
|
| Researcher Co-Investigators: |
|
| Project Partners: |
|
| Department: |
Physics |
| Organisation: |
Imperial College London |
| Scheme: |
Standard Research |
| Starts: |
01 October 2007 |
Ends: |
30 June 2008 |
Value (£): |
84,898
|
| EPSRC Research Topic Classifications: |
| Materials Characterisation |
Materials Synthesis & Growth |
|
| EPSRC Industrial Sector Classifications: |
|
| Related Grants: |
|
| Panel History: |
|
|
Summary on Grant Application Form |
|
There is a growing need for fast pulsed solid state lasers for materials processing, metrology, biomedicine and telecommunications applications. Medical applications include ultrashort pulses as scalpels in surgery, detection of cancer cells and eye surgery. For the telecommunications industry the large bandwidth of short pulse lasers and their high repetition rate would be ideal for wavelength division multiplexing (WDM) and time division multiplexing (TDM) applications, particularly at the important wavelengths of 1300 nm and 1550 nm. Such lasers must be compact, reliable and robust if they are to find commercial applications. Ultrafast dye lasers do not meet these requirements and the best candidate for real world applications is the diode pumped all solid-state passively mode-locked laser. There has been steady progress toward this goal over the last decade utilising semiconductor saturable absorber mirrors (SESAMs) as the passive mode locking element. A SESAM consists of a multilayer mirror with a stop band (high reflectivity region) which straddles the lasing wavelength with an absorber layer in the region between the DBR and the surface. The entire structure can be monolithically grown by epitaxial techniques such as MBE. This is a crucial requirement since the relatively high value of Fresnel reflection at an AlAs/GaAs interface means that high mirror reflectivities can achieved with a reasonable (~20) number of layers giving GaAs- based devices a major advantage over InP-based devices. The absorber is usually a quantum well (QW) whose absorption band edge can be tuned to the lasing wavelength. A fraction of the light incident on the device is absorbed and will not reach the mirror but increasing the intensity of the light saturates the absorption channel and the light penetrates through to the mirror where it is reflected. Consequently the reflectivity of the device varies typically by a few percent depending on the intensity of the incident light. Following absorption, the absorber layer can recover through two processes: thermalisation and radiative/non-radiative recombination of the photogenerated carriers. When the device is incorporated in the cavity of a solid state laser, temporal variations in the laser output modulate the mirror reflectivity and after many round trips, attenuation of the low intensity light leads to single short pulse or, in the frequency domain - longitudinal modes are phase shifted each round trip such that there is a definite relationship between the modes, producing a train of mode-locked pulses with a frequency given by the round trip in the laser cavity.
|
|
Key Findings |
|
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
|
|
Potential use in non-academic contexts |
|
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
|
|
Impacts |
|
| Description |
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk |
| Summary |
|
| Date Materialised |
|
|
|
|
Sectors submitted by the Researcher |
|
This information can now be found on Gateway to Research (GtR) http://gtr.rcuk.ac.uk
|
| Project URL: |
|
| Further Information: |
|
| Organisation Website: |
http://www.imperial.ac.uk |