Cuong Dang Group

THE CAVITY-LESS LASER

Amplified Spontaneous Emission

The transition from spontaneous emission to amplified spontaneous emission (ASE) when the excitation increases above threshold. The bright spot at the edge of the film is ASE

Without resonant cavity, this is cavity-less laser. It satisfies the definition of laser: Light Emission by Stimulated Emission of Radiation.

Increasing the size of the nanocrystals, the emission wavelength increases from blue to red.

ASE is getting easier

A capacitor device is utilized to apply electric field on a CQD film. Electric field introduces charges inside CQDs.

Charges in CQDs reduce the threshold for population inversion but lower the emission efficiency.

An optimum charging level can balance these two effects and enable the lowest amplified spontaneous emission threshold.

The Emission and Absorption Spectra

The threshold behaviour of ASE with narrower spectrum and increased intensity suddently after the excitation increases above threshold levels.

ASE emerges at the tail of absorption spectrum where the absoption is low

ASE can be blue or red shifted depending on the size of Stoke shift

THE QUANTUM DOT LASER

The World First Quantum Dot Laser Beam

The world first Quantum Dot Vertical Cavity Surface Emitting Laser (QD-VCSEL) enabled the first QD laser beam

For QDs, it turned out to be easy to make the most challenging laser configuration.

The QD Distributed Feedback Laser

The second order DFB configuration.

Spin-coating a layer of QD on top of resonant quartz grating

Surface Emission

The Cicular QD Distributed Feedback Laser

The second order DFB configuration with cicular grating.

Surface emitting beam without any correction lens