Stimulated emission on the ultraviolet and blue transitions in Cs has been achieved by pumping via two-photon absorption and four-wave mixing for the pump transition 62S12→82D32,52. The emission performance of the optically pumped cesium vapor laser operating in ultraviolet and blue has been extended to 650 nJ/pulse for 387 nm, 1 to 3 μJ/pulse for 388 nm, 200 nJ/pulse for 455 nm, and 500 nJ/pulse for 459 nm. Emission performance improves dramatically as the cesium vapor density is increased, and no scaling limitations associated with energy pooling or ionization kinetics have been observed.
Vertical external cavity surface emitting lasers (VECSELs) provide a laser design platform in order to explore
a variety of systems, and their flexibility eases this exploration. Moreover, their high-brightness operation
makes them attractive for many applications. In considering the methods of coupling VECSELs as well as
their potential uses, we begin by reporting on the development of a gain coupled VECSEL for use in optical
switching. In particular, two VECSEL cavities share a common gain region; the competition for a common set
of carriers dictate how these cavities interact. The easiest manifestation to realize gain coupling is to utilize
a linear cavity as well as a v-cavity, built around a single half-vertical cavity surface-emitting laser (VCSEL)
chip. The cavity gain/loss of each cavity can be controlled independently through use of birefringent filters,
allowing us to explore the design space, which can be divided up into coarse behavior, easy to analyze through
comparing the two uncoupled lasers, and a fine behavior, where one cavity will affect the other and each cavity
can lase simultaneously, sometimes at dramatically different wavelengths. These two regions may be explained
with simple rate equations, and it will be shown that if prepared properly, spontaneous emission plays a large
role in balancing the two laser cavities within the fine regime, while may be completely neglected in the coarse
regime.
Vertical external cavity surface emitting lasers (VECSELs) have captured the interest of high-brightness semiconductor
researchers, primarily due to their simplicity in design, power scalability, and "open cavity architecture,"
wherein it is simple to integrate nonlinear elements into the cavity. Through direct emission and indirect
(frequency-converted) means, wavelengths from the UV through to the mid-wave infrared regimes have been
demonstrated, increasing the suitability of the VECSEL platform for multiple applications. This presentation
outlines recent progress in VECSELs, measurements, novel cavities, and potential applications for these lasers.
The small signal modulation of a vertical external cavity surface emitting laser (VECSEL) is examined. The
modulation transfer function (MTF) of the cavity is measured for multiple photon lifetimes operating between
Class A and Class B regimes, where the photon and carrier lifetimes are of the same order. Three coupled ordinary
differential equations with similarities to an electrically-injected quantum-well laser with a separate confinement
heterostructure are used to mathematically describe the time-dependant VECSEL response. We present a series
of measurements that provide important laser parameters such as internal device losses and differential gain.
The VECSEL operating in this regime is an overdamped oscillator and has free-running characteristics that are
not unlike quantum-dot and quantum-cascade lasers.
This work investigates the linewidth enhancement factor (alpha-factor) and stability of an optically-injected
InAs/InGaAs quantum-dot Fabry-Perot laser. Using the injection-locking technique, the above threshold alpha-factor is
measured to be as low as 0.6 at 1.3X the threshold current. The below threshold alpha-factor is also measured using the
Hakki-Paoli technique. The measured alpha-factor values are used to simulate the dynamic response (stable locking,
period-one, period-doubling, or chaos) in the context of single-mode rate equations under zero-detuning injection
conditions for external injected power ratios ranging from -11dB to +15dB and slave current bias levels of 1.3X, 2X, and
2.6X threshold. Legacy literature has shown that optically-injected diode lasers typically follow the period-doubling
route into a chaotic region as the injection level is increased. Simulations show that at 2X the threshold current, a small
region of period-one operation will be observed followed by stable-locking as the injection ratio is increased. This
predominantly stable behavior is driven largely by the low alpha-factor. Experimental results support this prediction,
where under zero-detuning conditions, only unlocked and stable-locking operation is observed. Experimentally, periodone
operation was not observed at a slave laser bias current of 2X threshold, as it was predicted to occur below an
external power ratio of -20 dB, a level which was not attainable in this work. Such findings suggest that a quantum-dot
device can be employed in an optically-injected configuration for photonic tunable-clock applications.
The microwave domain modulation response of an injection-locked laser system is analyzed in the context of a Quantum
Dash Fabry-Perot laser. This work demonstrates the applicability of a newly-derived modulation response function by
using it to least-squares fit data collected on an injection-locked system with a Quantum-Dash Fabry-Perot
semiconductor slave laser. The maximum injection strength, linewidth enhancement factor, coupled phase between the
master and slave, and field enhancement factor characterizing the deviation of the locked slave laser from its freerunning
value are extracted by least-squares fitting the collected data with the function. The extracted values are then
compared with theoretically expected values under the given detuning conditions. The correlation between the frequency
of the resonance peak of the modulation response at the positive frequency detuning edge and a pole in the modulation
response function under this detuning condition is illustrated. The calculation of the injection strength based on the
experimental operating conditions is verified by applying the modulation response function to the experimental data.
With the modulation response function, injection-locked behaviors can be accurately simulated in the microwave domain
and used to predict operating conditions ideal for high-performance RF links.
We report on the performance of seeded Raman fiber amplifiers based on multimode gradient index fiber. The "beam
cleanup" improvement in beam quality of the Stokes beam over that of input pump beam (previously observed in
unseeded fiber amplifier geometries using stimulated Raman scattering in multimode graded index fiber) is shown here
to be limited by the beam quality of the input seed beam for seeded amplifier configurations. The amplifiers are
characterized in terms of their capacity for beam-cleanup, their ability to amplify the seed and in terms of their output
spectra. The advantages and disadvantages of a backward-pumped geometry versus a forward-pumped geometry are
discussed. Depending on the geometry, amplified power can be readily distributed to a cascade of Stokes frequencies
(unseeded forward-pumped geometry) or can be mostly contained in the seed frequency (seeded backward-pumped
geometry).
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