ABSTRACT We have investigated the lasing modes of oxide-confined vertical-cavity surface emitting... more ABSTRACT We have investigated the lasing modes of oxide-confined vertical-cavity surface emitting lasers (VCSELs). The individual Laguerre–Gaussian modes have been spectrally and spatially resolved with scanning confocal microscope with time resolution of 4 ps. Subject to the injection of ultrafast laser pulses, the VCSEL showed irregular pulsed emission which indicates the potential for transverse mode-locking of the VCSEL.
ABSTRACT Single-mode vertical-cavity surface-emitting lasers (VCSELs) have been investigated with... more ABSTRACT Single-mode vertical-cavity surface-emitting lasers (VCSELs) have been investigated with ultrafast optical modulation. After injection of a subpicosecond laser pulse into the VCSEL cavity, nonlasing modes were excited and produced optical beating in the emission of the VCSEL. After these oscillations have died down, when the VCSEL is operating at high power and when the injected laser pulses exceed a power threshold as well, the injected laser pulses can induce the lasing to switch to a normally nonlasing mode with crossed polarization. Our measurements of the decay time of the nonlasing modes at low injected pulse energy are consistent with the interpretation of this switching as enabled by increased lifetime of the nonlasing modes at high power.
ABSTRACT Based on time-resolved microscopic photoluminescence (μPL) from single self-assembled Ga... more ABSTRACT Based on time-resolved microscopic photoluminescence (μPL) from single self-assembled GaAs/AlxGa1−xAs quantum dots, we identify one of the emission lines as arising from positive trions (two holes and one electron) in these nominally undoped quantum dots. The trion is formed via tunneling of one electron out of the dot after optical excitation of a biexciton. The rise time of trion emission line matches the decay of the biexciton due to electron tunneling.
Hierarchically self-assembled GaAs/AlGaAs quantum dots are promising building blocks for quantum ... more Hierarchically self-assembled GaAs/AlGaAs quantum dots are promising building blocks for quantum information processing and novel lasers because they combine the tight confinement of InGaAs dots with the size homogeneity and a shorter emission wavelength of the GaAs/AlGaAs system at which many photodetectors are especially sensitive. So far, the emission dynamics of these structures has been unexplored. With a streak camera connected to a confocal microscope, we have measured the luminescence dynamics after direct optical picosecond excitation into the quantum dot states at a sample temperature of 10 K. Ensembles of high-density quantum dots (30 dots/µm 2) with well-separated transitions give information on state filling as well as intra-and interband relaxation. Single quantum dots on low-density samples (0.5 dots/µm 2) with microelectronvolt emission line widths reveal furthermore the time scale of biexciton formation and decay, as well as coherent effects.
Technical Digest. Summaries of Papers Presented at the International Quantum Electronics Conference. Conference Edition. 1998 Technical Digest Series, Vol.7 (IEEE Cat. No.98CH36236)
We report on a general approach to coherent control in semiconductors, based on optical waveforms... more We report on a general approach to coherent control in semiconductors, based on optical waveforms with synthesized intensity and phase versus time. This technique is limited only by the bandwidth of the initial laser pulses and the spectral resolution of the pulse-shaping apparatus. It is therefore especially suitable to investigate effects such as off-resonant Rabi oscillations and polaritons in multiple quantum wells. Experiments were performed in four-wave mixing (FWM) and differential reflection geometry based on a mode-locked Ti:sapphire laser emitting 100-fs pulses.
burgh-Vertical-cavity surface-emitting lasers (VCSEL's) are important devices for optical communi... more burgh-Vertical-cavity surface-emitting lasers (VCSEL's) are important devices for optical communication and sensing. Many applications require single-mode operation, which can be achieved by suppressing multiple lateral modes with emission apertures of 10 micrometers or less and by restricting emission to one polarization by reduction of symmetry. Such single-mode lasers still can produce multi-mode emission when subject to high pump currents or high-frequency modulation. Here we will discuss the emission dynamics of single-mode VCSEL's after resonant optical injection of femtosecond pulses from a mode-locked Ti:sapphire laser. The VCSEL emission is time and polarization resolved by cross correlation on a nonlinear optical crystal. This all-optical technique gives access to the VCSEL dynamics without limitation from electronics. Our measurements show dynamics in the 10 GHz range stemming from ordinary and from polarization relaxation oscillations. Interference beats above 100 GHz show the importance of dynamic multi-mode behavior. The decay of these beats gives direct information on the roundtrip gain of the dynamically excited modes. Polarization resolved measurements show the feasibility of polarization switching on a subpicosecond time scale.
Technical Digest. Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 1999
Summary form only given. Coherent control of carrier dynamics in solids has become a field of lar... more Summary form only given. Coherent control of carrier dynamics in solids has become a field of large interest within the last years. The well understood band-structure and picosecond dephasing times of optical transitions have made semiconductors the favourite systems for experimental investigations. Typical phase relaxation times of the order of a few femtoseconds in metals have limited optical spectroscopy in metals largely to incoherent phenomena. Recent developments in femtosecond laser technology, however, have yielded direct access to coherent optical phenomena in metallic electron systems.
CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009
Coherent control on the nanoscale has gained a lot of interest in the last years in theory [1] an... more Coherent control on the nanoscale has gained a lot of interest in the last years in theory [1] and experiment [2,3]. In this work we present a new method of coherent control of the material polarization in a nanoplasmonic system within a few tens of femtoseconds. We show that the ...
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009
The concept of coherent control has gained a lot of interest in the last years. It was originally... more The concept of coherent control has gained a lot of interest in the last years. It was originally developed for applications such as quantum control in molecular processes [1] and subsequently transferred to semiconductors, where the time dynamics of excitons have been controlled ...
2012 17th Opto-Electronics and Communications Conference, 2012
ABSTRACT A graphene-based saturable absorber was fabricated by optically depositing layers of gra... more ABSTRACT A graphene-based saturable absorber was fabricated by optically depositing layers of graphene onto the end tip of single mode fiber, and it was used to passively Q-switch thulium-doped fiber laser at 2 μm pumped by EDFA. The spectrum of the graphene Q-switched thulium-doped fiber laser and the relationship between the output power, repetition rate and pump strength are studied and presented.
Ultrafast Lasers Probe Phenomena in Semiconductors and Superconductors, 1992
Tunneling transfer in various GaAs/Al0.35Ga0.65As asymmetric double quantum well structure is stu... more Tunneling transfer in various GaAs/Al0.35Ga0.65As asymmetric double quantum well structure is studied by time-resolved photoluminescence measurements in the pico- and femtosecond regime. A large variety of electron and hole resonances is detected when electric fields of both signs are externally applied. The ground state resonance shifts, when the electrons tunnel in the reverse direction, revealing the importance of excitonic effects. Longitudinal optical phonon assisted tunneling plays a minor role for narrow quantum wells in comparison to impurity or interface roughness assisted transfer. Resonant electron tunneling times depend exponentially on the square root of integrated tunneling barrier height and are an order of magnitude faster than resonant hole tunneling times. The n equals 2 to n equals 1 electronic intersubband scattering time in a 10 nm quantum well is determined to be 550 fs measuring the transfer time through a thin barrier.
Summaries of Papers Presented at the Lasers and Electro-Optics. CLEO '02. Technical Diges, 2002
Summary form only given. We have shown high repetition rate picosecond mode-locking in a VCSEL th... more Summary form only given. We have shown high repetition rate picosecond mode-locking in a VCSEL that provides extremely low jitter. These results are promising for the development of compact and efficient ultra-fast pulse sources. Using VCSELs as mode-locked sources has additional advantages over existing technologies, allowing for integration in 2-D arrays and electrically tunable repetition rates. This work provides new examples of transverse nonlinear optics in micro-cavity lasers including transverse mode-locking and sub-harmonic mode-locking.
Interference effects between ultrafast laser pulses become important when the relative phase is p... more Interference effects between ultrafast laser pulses become important when the relative phase is precisely determined. The response of an optical system then shows strong oscillations when the pump-pulse separation is changed.1–4 These oscillations appear even for non-overlapping pulses as long as the phase relaxation time of the optical transition exceeds the pump-pulse separation. This interference spectroscopy, in contrast to other coherent optical techniques,5 gives direct access to the phase evolution in time, which is especially interesting in semiconductors because many-body interactions cause distinct departures from expected behavior of ideal two-level systems.6, 7
ABSTRACT We have investigated the lasing modes of oxide-confined vertical-cavity surface emitting... more ABSTRACT We have investigated the lasing modes of oxide-confined vertical-cavity surface emitting lasers (VCSELs). The individual Laguerre–Gaussian modes have been spectrally and spatially resolved with scanning confocal microscope with time resolution of 4 ps. Subject to the injection of ultrafast laser pulses, the VCSEL showed irregular pulsed emission which indicates the potential for transverse mode-locking of the VCSEL.
ABSTRACT Single-mode vertical-cavity surface-emitting lasers (VCSELs) have been investigated with... more ABSTRACT Single-mode vertical-cavity surface-emitting lasers (VCSELs) have been investigated with ultrafast optical modulation. After injection of a subpicosecond laser pulse into the VCSEL cavity, nonlasing modes were excited and produced optical beating in the emission of the VCSEL. After these oscillations have died down, when the VCSEL is operating at high power and when the injected laser pulses exceed a power threshold as well, the injected laser pulses can induce the lasing to switch to a normally nonlasing mode with crossed polarization. Our measurements of the decay time of the nonlasing modes at low injected pulse energy are consistent with the interpretation of this switching as enabled by increased lifetime of the nonlasing modes at high power.
ABSTRACT Based on time-resolved microscopic photoluminescence (μPL) from single self-assembled Ga... more ABSTRACT Based on time-resolved microscopic photoluminescence (μPL) from single self-assembled GaAs/AlxGa1−xAs quantum dots, we identify one of the emission lines as arising from positive trions (two holes and one electron) in these nominally undoped quantum dots. The trion is formed via tunneling of one electron out of the dot after optical excitation of a biexciton. The rise time of trion emission line matches the decay of the biexciton due to electron tunneling.
Hierarchically self-assembled GaAs/AlGaAs quantum dots are promising building blocks for quantum ... more Hierarchically self-assembled GaAs/AlGaAs quantum dots are promising building blocks for quantum information processing and novel lasers because they combine the tight confinement of InGaAs dots with the size homogeneity and a shorter emission wavelength of the GaAs/AlGaAs system at which many photodetectors are especially sensitive. So far, the emission dynamics of these structures has been unexplored. With a streak camera connected to a confocal microscope, we have measured the luminescence dynamics after direct optical picosecond excitation into the quantum dot states at a sample temperature of 10 K. Ensembles of high-density quantum dots (30 dots/µm 2) with well-separated transitions give information on state filling as well as intra-and interband relaxation. Single quantum dots on low-density samples (0.5 dots/µm 2) with microelectronvolt emission line widths reveal furthermore the time scale of biexciton formation and decay, as well as coherent effects.
Technical Digest. Summaries of Papers Presented at the International Quantum Electronics Conference. Conference Edition. 1998 Technical Digest Series, Vol.7 (IEEE Cat. No.98CH36236)
We report on a general approach to coherent control in semiconductors, based on optical waveforms... more We report on a general approach to coherent control in semiconductors, based on optical waveforms with synthesized intensity and phase versus time. This technique is limited only by the bandwidth of the initial laser pulses and the spectral resolution of the pulse-shaping apparatus. It is therefore especially suitable to investigate effects such as off-resonant Rabi oscillations and polaritons in multiple quantum wells. Experiments were performed in four-wave mixing (FWM) and differential reflection geometry based on a mode-locked Ti:sapphire laser emitting 100-fs pulses.
burgh-Vertical-cavity surface-emitting lasers (VCSEL's) are important devices for optical communi... more burgh-Vertical-cavity surface-emitting lasers (VCSEL's) are important devices for optical communication and sensing. Many applications require single-mode operation, which can be achieved by suppressing multiple lateral modes with emission apertures of 10 micrometers or less and by restricting emission to one polarization by reduction of symmetry. Such single-mode lasers still can produce multi-mode emission when subject to high pump currents or high-frequency modulation. Here we will discuss the emission dynamics of single-mode VCSEL's after resonant optical injection of femtosecond pulses from a mode-locked Ti:sapphire laser. The VCSEL emission is time and polarization resolved by cross correlation on a nonlinear optical crystal. This all-optical technique gives access to the VCSEL dynamics without limitation from electronics. Our measurements show dynamics in the 10 GHz range stemming from ordinary and from polarization relaxation oscillations. Interference beats above 100 GHz show the importance of dynamic multi-mode behavior. The decay of these beats gives direct information on the roundtrip gain of the dynamically excited modes. Polarization resolved measurements show the feasibility of polarization switching on a subpicosecond time scale.
Technical Digest. Summaries of Papers Presented at the Quantum Electronics and Laser Science Conference, 1999
Summary form only given. Coherent control of carrier dynamics in solids has become a field of lar... more Summary form only given. Coherent control of carrier dynamics in solids has become a field of large interest within the last years. The well understood band-structure and picosecond dephasing times of optical transitions have made semiconductors the favourite systems for experimental investigations. Typical phase relaxation times of the order of a few femtoseconds in metals have limited optical spectroscopy in metals largely to incoherent phenomena. Recent developments in femtosecond laser technology, however, have yielded direct access to coherent optical phenomena in metallic electron systems.
CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference, 2009
Coherent control on the nanoscale has gained a lot of interest in the last years in theory [1] an... more Coherent control on the nanoscale has gained a lot of interest in the last years in theory [1] and experiment [2,3]. In this work we present a new method of coherent control of the material polarization in a nanoplasmonic system within a few tens of femtoseconds. We show that the ...
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference, 2009
The concept of coherent control has gained a lot of interest in the last years. It was originally... more The concept of coherent control has gained a lot of interest in the last years. It was originally developed for applications such as quantum control in molecular processes [1] and subsequently transferred to semiconductors, where the time dynamics of excitons have been controlled ...
2012 17th Opto-Electronics and Communications Conference, 2012
ABSTRACT A graphene-based saturable absorber was fabricated by optically depositing layers of gra... more ABSTRACT A graphene-based saturable absorber was fabricated by optically depositing layers of graphene onto the end tip of single mode fiber, and it was used to passively Q-switch thulium-doped fiber laser at 2 μm pumped by EDFA. The spectrum of the graphene Q-switched thulium-doped fiber laser and the relationship between the output power, repetition rate and pump strength are studied and presented.
Ultrafast Lasers Probe Phenomena in Semiconductors and Superconductors, 1992
Tunneling transfer in various GaAs/Al0.35Ga0.65As asymmetric double quantum well structure is stu... more Tunneling transfer in various GaAs/Al0.35Ga0.65As asymmetric double quantum well structure is studied by time-resolved photoluminescence measurements in the pico- and femtosecond regime. A large variety of electron and hole resonances is detected when electric fields of both signs are externally applied. The ground state resonance shifts, when the electrons tunnel in the reverse direction, revealing the importance of excitonic effects. Longitudinal optical phonon assisted tunneling plays a minor role for narrow quantum wells in comparison to impurity or interface roughness assisted transfer. Resonant electron tunneling times depend exponentially on the square root of integrated tunneling barrier height and are an order of magnitude faster than resonant hole tunneling times. The n equals 2 to n equals 1 electronic intersubband scattering time in a 10 nm quantum well is determined to be 550 fs measuring the transfer time through a thin barrier.
Summaries of Papers Presented at the Lasers and Electro-Optics. CLEO '02. Technical Diges, 2002
Summary form only given. We have shown high repetition rate picosecond mode-locking in a VCSEL th... more Summary form only given. We have shown high repetition rate picosecond mode-locking in a VCSEL that provides extremely low jitter. These results are promising for the development of compact and efficient ultra-fast pulse sources. Using VCSELs as mode-locked sources has additional advantages over existing technologies, allowing for integration in 2-D arrays and electrically tunable repetition rates. This work provides new examples of transverse nonlinear optics in micro-cavity lasers including transverse mode-locking and sub-harmonic mode-locking.
Interference effects between ultrafast laser pulses become important when the relative phase is p... more Interference effects between ultrafast laser pulses become important when the relative phase is precisely determined. The response of an optical system then shows strong oscillations when the pump-pulse separation is changed.1–4 These oscillations appear even for non-overlapping pulses as long as the phase relaxation time of the optical transition exceeds the pump-pulse separation. This interference spectroscopy, in contrast to other coherent optical techniques,5 gives direct access to the phase evolution in time, which is especially interesting in semiconductors because many-body interactions cause distinct departures from expected behavior of ideal two-level systems.6, 7
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Papers by Albert Heberle