New developments and applications of tunable IR lead salt lasers

Semiconductor saturable absorber mirrors (SESAMs) using quantum dot (QD) absorbers exhibit a larger design freedom than standard quantum well absorbers. The additional parameter of the dot density in combination with the field enhancement allows for an independent control of saturation fluence and modulation depth. We present the first detailed study of the effect of QD growth parameters and post growth annealing on the macroscopic optical SESAM parameters, measuring both nonlinear reflectivity and recombination dynamics. We studied a set of self-assembled InAs QD-SESAMs optimized for an operation wavelength around 960 nm with varying dot density and growth temperature. We confirm that the modulation depth is controlled by the dot density. We present design guidelines for QD-SESAMs with low saturation fluence and fast recovery, which are for example important for modelocking of vertical external cavity surface emitting lasers (VECSELs).

Growth parameter optimization for fast quantum dot SESAMs.

Excitons, the bound states of an electron and a hole in a solid material, play a key role in the optical properties of insulators and semiconductors. Here, we report the observation of excitons in bilayer graphene (BLG) using photocurrent spectroscopy of high-quality BLG encapsulated in hexagonal boron nitride. We observed two prominent excitonic resonances with narrow line widths that are tunable from the mid-infrared to the terahertz range. These excitons obey optical selection rules distinct from those in conventional semiconductors and feature an electron pseudospin winding number of 2. An external magnetic field induces a large splitting of the valley excitons, corresponding to a g-factor of about 20. These findings open up opportunities to explore exciton physics with pseudospin texture in electrically tunable graphene systems​.

https://par.nsf.gov/servlets/purl/10074479

Tunable excitons in bilayer graphene

Semiconductor lasers are the most efficient man-made narrow-band light sources and convert up to three-quarters of electric energy into light High-power diode lasers are characterized by very high internal power densities in their small cavity, resulting in local heating and sometimes device degradation Catastrophic optical damage (COD) of diode lasers is a relevant degradation mechanism and limit for reaching ultra-high optical powers An overview is given on research activities targeting the mechanisms being relevant for the COD process in GaAs-based diode lasers emitting in the 630―1100 nm range The discussion of experiments, where COD is artificially provoked, represents the main topic The sequence of events and fast kinetics taking place on a nanosecond to microsecond time scale are addressed A particular emphasis is laid on recent experimental work performed in the authors' laboratories Paving the way for knowledge-based solutions towards more robust diode lasers represents the ultimate goal of this work COD diagram determined for a batch of broad-area AlGaAs diode lasers The time to COD within a single current pulse is plotted versus the actual average optical power in the moment when the COD takes place Full circles stand for clearly identified COD events (right ordinate), whereas open circles (left ordinate) represent the pulse duration in experiments, where no COD has been detected A borderline (gray) exists between two regions, i e, parameter sets, of presence (orange) and absence of COD (blue) This borderline is somewhat blurred because of the randomness in filamentation of the laser nearfield and scatter in properties of the involved individual devices

Mechanisms and fast kinetics of the catastrophic optical damage (COD) in GaAs-based diode lasers

Tunable Excitons in Bilayer Graphene

Transient photoluminescence from a series of asymmetric InAs quantum-dot bilayers with a GaAs barrier layer thickness varying from 30 to 60 monolayers between the quantum-dot planes is investigated. The interdot carrier transfer process is analyzed. In the framework of a three-level system, interdot carrier transfer times between 200 and 2500ps are derived and compared with similar data from the literature. Within the semiclassical Wentzel–Kramers–Brillouin approximation, the observed “transfer time-barrier thickness-relation” supports nonresonant tunneling as the microscopic carrier transfer mechanism.

Interdot carrier transfer in asymmetric bilayer InAs∕GaAs quantum dot structures

On s'interesse particulierement a la photoluminescence infra-rouge dans des composes II-VI a bande interdite etroite, et plus specialement au Hg 1-x Cd x Te. On etudie egalement la luminescence dans les sels de plomb et a l'influence du dopage, de l'alliage et de la perfection structurale

Infrared Photoluminescence in Narrow‐Gap Semiconductors

Aging properties of AlGaAs high power laser arrays were monitored by photocurrent (PC) measurements. We demonstrate that this method allows a quantitative analysis of the aging process and provides insight into the microscopic degradation mechanisms. In graded index separate confinement heterostructures, the PC spectra in the spectral range of the laser transition display a substantial current decrease with aging. This is attributed to enhanced rates of surface recombination and defect generation in the graded gap region. In contrast, step index structures exhibit a much smaller change of PC. The PC results are complemented by measurements of low-frequency laser current noise and front facet temperature.

Monitoring of aging properties of AlGaAs high-power laser arrays

Presentation des resultats sur la detection et les parametres spectroscopiques de CO, CO 2 et SO 2 par spectroscopie laser haute resolution. L'application de cette methode pour la detection de ppm de CO de l'atmosphere illustre la sensibilite de l'appareillage

Detection of carbon monoxide, carbon dioxide and sulfur dioxide with pulsed tunable PbS1-xSex-diode lasers

Carrier transfer in $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ asymmetric quantum dot pairs has been studied by means of continuous-wave and time-resolved photoluminescence in a bilayer $\mathrm{In}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ quantum dots system. The dependence of the tunneling time on the thickness of the separation layer is determined and the tunneling time is found to span the range from $250\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}2500\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$. A microscopic model of carrier transfer, including nonresonant electron tunneling from a direct into a cross exciton state, with subsequent generation of two direct excitons in adjacent quantum dot layers, is proposed.

J. W. Tomm

Papers

Interdot carrier transfer in asymmetric bilayer InAs∕GaAs quantum dot structures

Infrared Photoluminescence in Narrow‐Gap Semiconductors

Monitoring of aging properties of AlGaAs high-power laser arrays

Detection of carbon monoxide, carbon dioxide and sulfur dioxide with pulsed tunable PbS1-xSex-diode lasers

Nonresonant tunneling carrier transfer in bilayer asymmetric InAs/GaAs quantum dots