consumption and financial burden of the multiple light sources required for such systems. The AlGaInN material system allows for single transverse mode laser diodes to be fabricated with optical powers up to 100 mW over a wide range from ~380 nm up to ~530 nm. By tuning the indium content and thickness of the GaInN quantum well, we have developed a range of AlGaInN diode-lasers targeted to meet the wavelength and power requirements suitable for optical clocks and atom interferometry systems.
One of the major limiting factors in nitride laser diode development has been the lack of a suitable low defectivity and uniform GaN substrate. Recently, single crystal growth of large area, very low dislocation-density and uniform GaN substrates are grown using a combination of high temperature and high pressure enabling a range of AlGaInN laser technology to be developed. This direct light generation at the required wavelength is crucial to reduce complexity and size of the overall system, and to ensure a high wall-plug efficiency that is critical for space and mobile applications.
We will present our development of GaN based, low SWaP, frequency-stabilised external-cavity seed and tapered amplifiers to operate at 461nm for first stage strontium cooling. This includes growth of custom optimised GaN epitaxy for operation at 461 nm, a robust ECDL geometry, a novel tapered amplifier design and important work in characterising the optical performance and minimising surface reflectivity to identify suitable working parameters.
GaN laser diodes have the potential to be a key enabling technology since the AlGaInN material system allows for laser diodes to be fabricated over a wide range of wavelengths from the u.v. to the visible. Novel applications include high power laser bars for optical pumping, to laser sources for quantum technologies based on atom interferometry, such as next generation optical clocks and gravity sensors.
We report our latest results on a range of AlGaInN diode-lasers targeted to meet the linewidth, wavelength and power requirements suitable for optical clocks and atom interferometry systems. This includes the [5s2S1/2-5p2P1/2] cooling transition in strontium+ ion optical clocks at 422 nm, the [5s21S0-5p1P1] cooling transition in neutral strontium clocks at 461 nm and the [5s2s1/2 – 6p2P3/2] transition in rubidium at 420 nm.
In addition, we report our latest results on tapered high power GaN laser diodes, for i) optical amplifiers, and ii) optimising the optical power of the device by reducing filamentation and hence avoiding catastrophic optical mirror damage (COMD).
GaN laser diodes has the potential to be a key enabling technology for a range of quantum technologies, including next generation optical atomic clocks and gravity sensors, based on cold-atom interferometry and also quantum communications, that have important applications for security and defence. Presently, such systems require a number of expensive, sophisticated and complex laser sources that limit quantum technologies to the laboratory. In contrast, GaN laser diode technology has the potential to provide a compact, rugged and reliable solutions, suitable for commercialisation. We report our latest results of GaN laser diodes suitable for both cold-atom interferometry and quantum communications.
GaN laser diodes fabricated from the AlGaInN material system is an emerging technology for
high power, optical integration and quantum applications. The AlGaInN material system allows
for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the
visible ~530nm, by tuning the indium content of the laser GaInN quantum well, giving rise to
new and novel applications including displays and imaging systems, free-space and underwater
telecommunications and the latest quantum technologies such as optical atomic clocks and atom
There are two physical phenomena governing the light emission in InGaN quantum structures: the internal electric fields and the In composition fluctuations. Both these effects manifest through the blue shift of the wavelength emission with the excitation intensity and both of them have the pronounced influence on the light emitting properties of these structures.
In order to discriminate between these two effects, we fabricated two identical structures: one with the quantum barriers doped with silicon (method for internal electric field screening) and the other with an undoped active region. Under the optical excitation the emission peak shifts by almost 35 nm (Si doped) and 50nm (without Si). Additionally, we studied temperature dependence of the emission peak position. In case of low temperatures and at RT and high pumping energy, emission energy position is almost the same for both samples. Our observations lead us to the conclusion that at low temperatures and at high pumping regime the Quantum Confined Stark Effect (QCSE) is totally suppressed. While this is understandable that at high carrier injection QCSE is screened, the origin of the low temperature effect is much less clear. We can speculate that at the lowest temperature the carriers are localized eliminating the spatial separation of holes and electrons wavefunctions.
Measured cathodoluminescence (CL) maps show the same level of the indium fluctuations for both samples. At higher excitation the fluctuations starts to be less visible suggesting band filling of states.
Finally we compare recombination times by means of time resolved photoluminescence.