1,720,993 research outputs found
Passively modelocked surface-emitting semiconductor lasers
No full textThis paper will review and discuss pico- and femtosecond pulse generation from passively modelocked vertical–external-cavity
surface-emitting semiconductor lasers (VECSELs).We shall discuss the physical principles of ultrashort pulse generation in these lasers, considering in turn the role played by the semiconductor quantum well gain structure, and the saturable absorber. The paper will analyze the fundamental performance limits of these devices, and review the results that have been demonstrated to date. Different types of semiconductor saturable absorber mirror (SESAM) design, and their characteristic dynamics, are described in detail; exploring the ultimate goal of moving to a wafer integration approach, in which the SESAM is integrated into the VECSEL structure with tremendous gain in capability. In particular, the contrast between VECSELs and diode-pumped solid-state lasers and edge-emitting diode lasers will be discussed. Optically pumped VECSELs have led to an improvement by more than two orders of magnitude to date in the average output power achievable from a passively modelocked ultrafast semiconductor laser
Laser ions ring local modes first
No full textWe tend to think that lasers only produce light. In many solid-state lasers, however, just as much energy ends up as vibrations of the laser crystal as emerges in the laser beam. These vibrations are crucial to the operation of the laser because they carry excess energy away from the ion that produces laser emission. But we do not know how the ion transfers this energy into the lattice, in particular how each ion is able to release energies many times greater than those typical of thermal vibrations. Experiments by Dana Calistru and colleagues at City College in New York have now provided new insights into this mechanism that could lead to improved materials for solid-state lasers
Wetting-layer-pumped continuous wave surface emitting quantum dot laser
No full textWe report a continuous wave 1 μm laser based on InAs Stranski-Krastanov quantum dots (SK-QD) which is optically pumped on a wetting layer absorption band at 915 nm. The slope efficiency of this laser relative to absorbed pump power was measured to be 56% with wetting layer pumping, 1.75 times larger than when pumped with 830 nm light absorbed into the barriers between the SK-QD layers. Compared to barrier pumping, wetting layer pumping benefits from a smaller quantum defect, with less heat deposited in the active region, at the expense of weaker pump absorption in the thin (~1 nm) wetting layer. When a 50 μm thick intracavity diamond heatspreader was contacted to the optically pumped gain structure, a 10-fold increase in output power, up to 2.25W, was obtained in the barrier pumped case. A much smaller 2-fold increase in power, to a maximum of 0.35 W, was seen for the wetting layer pumped case. The diamond heatspreader is more effective in removing heat from the active region, where it is deposited by barrier pumping, than from the substrate, which absorbs residual pump radiation in the barrier pumping case. A gain sample with a doubly periodic DBR to back reflect pump radiation, will allow the full potential of wetting layer pumping to be realised, both by increasing pump absorption due to the double pass through the active region, and by localising heat generation in the active region.</p
Continuous-wave oscillation of Tm<sup>3+</sup>-doped fluorozirconate fibre lasers at around 1.47µm, 1.9µm and 2.3µm when pumped at 790nm
No full textContinuous operation of Tm3+-doped fluorozirconate fibre lasers at around 1.47m, 1.9µm and 2.3µm has been demonstrated when pumping at around 790nm with a Ti:sapphire laser. The efficiency of the 1.9 µm 3H4 - 3H6, transition was found to be significantly increased by enforcing simultaneous oscillation on the 3F4 - 3H5 transition at 2.3µm as this effectively enhances the branching ratio for pumping the 3H4 level. An upconversion process leading to blue emission has also been observed. The efficiency of this process is enhanced by more than an order of magnitude as soon as laser oscillation takes place at 2.3 µm, indicating the potential application of manipulating branching ratios via lasing
Amplification of photon echo signals by use of a fiber amplifier
Full text linkThe efficiency of photon-echo processes typically lies in the 0.1-1% range. For many photon-echo-based applications suggested in optical storage and all-optical communication the photon-echo output pulses would need to be used as input data to a new photon-echo process. In such cases amplification of the photon-echo output signals would be necessary for an acceptable signal-to-noise ratio to be obtained. We show that a Pr-doped ZBLAN fiber is able to produce significant amplification of photon-echo signals generated in Pr-doped Y2SiO5 at 606 nm
Fluoride fibre lasers
No full textSimultaneous laser oscillation near 2µm and 2.3µm on the 3H4 - 3H6 and 3F4 - 3H5 transitions respectively has been demonstrated in a thulium-doped fluorozirconate fiber when pumping at 0.79µm. Diode-pumped operation of the 3H4 - 3H6 transition has also been achieved. Pulsed laser emission at 1.72µm has been observed on the 4S3/2 - 4I9/2 transition in an erbium-doped fluorozirconate fiber when pumping at 488nm or 514nm
Saturated gain spectrum of VECSELs determined by transient measurement of lasing onset
Full text linkWe describe time-resolved measurements of the evolution of the spectrum of radiation emitted by an optically-pumped continuous-wave InGaAs-GaAs quantum well laser, recorded as lasing builds up from noise to steady state. We extract a fitting parameter corresponding to the gain dispersion of the parabolic spectrum equal to 79 30 fs2 and 36 6 fs2 for a resonant and anti-resonant structure, respectively. Furthermore the recorded evolution of the spectrum allows for the calculation of an effective FWHM gain bandwidth for each structure, of 11 nm and 18 nm, respectively.This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-6-6919. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.</p
New developments in THz-time domain spectroscopy involving ML-VECSELs
No full textThe THz time domain spectrometer (THz-TDS) has revolutionized the adoption of THz science in fields such as medicine, material characterization, pharmaceutical research and biology among others. Traditionally a THz-TDS was based on a titanium sapphire laser, while most of the commercially sold spectrometers today adopt fiber lasers. Vertical External Cavity Surface emitting lasers or VECSELs have potential to be the future laser of choice for the implementation of THz spectrometers, as they are small, low-cost, low noise and high repetition rate. Here I will outline the progress in our laboratory and the general community concerning VECSEL-THz technology and I will account the problems that have to be solved for the VECSEL-THz technology to succeed.</p
175 GHz, 400-fs-pulse harmonically mode-locked surface emitting semiconductor laser
Full text linkWe report a harmonically mode-locked vertical external cavity surface emitting laser (VECSEL) producing 400 fs pulses at a repetition frequency of 175 GHz with an average output power of 300 mW. Harmonic mode-locking was established using a 300 µm thick intracavity single crystal diamond heat spreader in thermal contact with the front surface of the gain sample using liquid capillary bonding. The repetition frequency was set by the diamond microcavity and stable harmonic mode locking was achieved when the laser cavity length was tuned so that the laser operated on the 117th harmonic of the fundamental cavity. When an etalon placed intracavity next to the gain sample, but not in thermal contact was used pulse groups were observed. These contained 300 fs pulses with a spacing of 5.9 ps. We conclude that to achieve stable harmonic mode locking at repetition frequencies in the 100s of GHz range in a VECSEL there is a threshold pulse energy above which harmonic mode locking is achieved and below which groups of pulses are observed
High-power quantum dot semiconductor disk lasers
No full textThe latest achievements of quantum dot based semiconductor disk lasers are reviewed. Several lasers operating at 1040 nm - 1260 nm were studied. All the structures were grown with molecular beam epitaxy on GaAs substrates. The number of quantum dot layers was varied and the gain was provided either by the ground or the excited state transition of the quantum dots. Frequency doubling of the lasers was demonstrated and the dual-gain laser geometry was found to be practical solution for intracavity frequency conversion. Intracavity heat spreader and thinned device heat management approaches are studied and compared
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