Gain Region Research Articles

The Effect of Quantum Noise on Multipartite Entanglement from a Cascaded Parametric Amplifier

The tripartite entanglement generated from a cascaded parametric amplifier is always present in the whole gain region in the ideal condition. However, in practical applications, the quantum entanglement is very fragile and easily deteriorated by quantum noise from interactions with external environments, e.g., the avoidable attenuation and amplification operations may lead to some degradation effects on the quantum entanglement. Therefore, in this work, bipartite entanglement for the three pairs and tripartite entanglement in this cascaded parametric amplifier under the circumstances of attenuation and amplification operations are analyzed by using positivity under partial transposition criterion. The results show that tripartite entanglement is robust to the deterioration effects from the attenuation and amplification operations rather than bipartite entanglement. Our results may find some practical applications of multipartite quantum entanglement in quantum secure communications.

100-GHz ultra-short high-peak-power colliding-pulse mode-locked laser with asymmetric coating.

By using colliding-pulse mode-locking (CPM) configuration with asymmetric cladding layer and coating, 1.5-µm AlGaInAs/InP multiple quantum well (MQW) CPM lasers with high-power and ultra-short pulse generation capability at a repetition rate of 100 GHz are reported. The laser adopts a high-power epitaxial design, with four pairs of MQWs and an asymmetrical dilute waveguide cladding layer to reduce the internal loss, maintaining good thermal conductivity while increasing the saturation energy of the gain region. The asymmetric coating is introduced, as compared to conventional CPM laser with symmetric reflectivity, to further increase the output power and shorten the pulse width. With a high reflection (HR) coating of 95% on one facet and another facet as cleaved, 100-GHz sub-picosecond optical pulses with peak power on a Watt level are demonstrated. Two mode-locking states, the pure CPM state and the partial CPM state, are investigated. Pedestal-free optical pulses are obtained for both states. For the pure CPM state, a pulse width of 564 fs, an average power of 59 mW, a peak power of 1.02 W, and an intermediate mode suppression ratio over 40 dB are demonstrated. For the partial CPM state, a pulse width of 298 fs is demonstrated.

Gain recovery dynamics in active type-II semiconductor heterostructures

Type-II heterostructures as active layers for semiconductor laser devices combine the advantages of a spectrally broad, temperature stable, and efficient gain with the potential for electrical injection pumping. Their intrinsic charge carrier relaxation dynamics limit the maximum achievable repetition rates beyond any constraints of cavity design or heat dissipation. Of particular interest are the initial build up of gain after high-energy injection and the gain recovery dynamics following depletion through a stimulated emission process. The latter simulates the operation condition of a pulsed laser or semiconductor optical amplifier. An optical pump pulse injects hot charge carriers that eventually build up broad spectral gain in a model (Ga,In)As/GaAs/Ga(As,Sb) heterostructure. The surplus energies of the optical pump mimic the electron energies typical for electrical injection. Subsequently, a second laser pulse tuned to the broad spectral gain region depletes the population inversion through stimulated emission. The spectrally resolved nonlinear transmission dynamics reveal gain recovery times as fast as 5 ps. These data define the intrinsic limit for the highest laser repetition rate possible with this material system in the range of 100 GHz. The experimental results are analyzed using a microscopic many-body theory identifying the origins of the broad gain spectrum.

Solution of fiber Raman amplifier model using binary search equation-based adaptive artificial bee colony algorithm

Due to the need for high bandwidth, there is growing interest in distributed fiber Raman amplifiers (FRA). In addition to having wide bandwidth, FRAs have the advantages of a low noise factor and simplicity of use. However, the optimization of the wavelength and power values of the pump lasers to be used in FRAs for a broadband and flat gain region is an important problem to be solved. In this study, a distributed FRA system was set using 100 signals with a 50-km propagation distance and 8 pump signals in the opposite direction, which were gain-flattened. The attenuation coefficient of SMF-28 type optical fiber was used in the system. First, optimum pump wavelengths and power levels were found by the binary search equation based adaptive artificial bee colony algorithm. Then, the FRA boundary value problem (BVP) was solved with the MATLAB BVP solver. Finally, the analytical Jacobian matrix required for the solution of the equation was included in the system, and faster and more effective results were obtained. The results show that the gain ripple of 100 optical signals was 0.5 dB at the maximum.

Core collapse supernova gravitational wave emission for progenitors of 9.6, 15, and 25M⊙

We present gravitational wave emission predictions based on three core collapse supernova simulations corresponding to three different progenitor masses. The masses span a large range, between 9.6 and $25{M}_{\ensuremath{\bigodot}}$, are all initially nonrotating, and are of two metallicities: zero and solar. We compute both the temporal evolution of the gravitational wave strains for both the plus and the cross polarizations, as well as their spectral decomposition and characteristic strains. The temporal evolution of our zero metallicity $9.6{M}_{\ensuremath{\bigodot}}$ progenitor model is distinct from the temporal evolution of our solar metallicity $15{M}_{\ensuremath{\bigodot}}$ progenitor model and our zero metallicity $25{M}_{\ensuremath{\bigodot}}$ progenitor model. In the former case, the high-frequency gravitational wave emission is largely confined to a brief time period $\ensuremath{\sim}75\text{ }\text{ }\mathrm{ms}$ after bounce, whereas in the latter two cases high-frequency emission does not commence until $\ensuremath{\sim}125\text{ }\text{ }\mathrm{ms}$ after bounce or later. The excitation mechanisms of the high-frequency emission in all three cases correspond to proto-neutron star convection and accretion onto the proto-neutron star from the convective gain layer above it, with the former playing the dominant role for most of the evolution. The low-frequency emission in all three models exhibits very similar behavior. At frequencies below $\ensuremath{\sim}250\text{ }\text{ }\mathrm{Hz}$, gravitational waves are emitted by neutrino-driven convection and the standing accretion shock instability (SASI). This emission extends throughout the simulations when a gain region is present. In all three models, explosion is observed at $\ensuremath{\sim}125$, $\ensuremath{\sim}500$, and $\ensuremath{\sim}250\text{ }\text{ }\mathrm{ms}$ after bounce in the 9.6, 15, and $25{M}_{\ensuremath{\bigodot}}$ progenitor models, respectively. At these times, the low-frequency gravitational wave emission is joined by very low-frequency emission, below $\ensuremath{\sim}10\text{ }\text{ }\mathrm{Hz}$. These very low-frequency episodes are the result of explosion and begin at the above designated explosion times in each of our models. Our characteristic strains tell us that, in principle, all three gravitational wave signals would be detectable by current-generation detectors for a supernova at a distance of 10 kpc. However, our $9.6{M}_{\ensuremath{\bigodot}}$ progenitor model is a significantly weaker source of gravitational waves, with strain amplitudes approximately 5--10 times less than in our other two models. The characteristic strain for this model tells us that such a supernova would be detectable only within a much more narrow frequency range around the maximum sensitivity of today's detectors. Finally, in our $9.6{M}_{\ensuremath{\bigodot}}$ progenitor model, we see very high-frequency gravitational radiation, extending up to $\ensuremath{\sim}2000\text{ }\text{ }\mathrm{Hz}$. This feature results from the interaction of shock- and deleptonization-induced convection with perturbations introduced in the progenitor by nuclear burning during core collapse. While unique to the $9.6{M}_{\ensuremath{\bigodot}}$ progenitor model analyzed here, this very high-frequency emission may, in fact, be a generic feature of the predictions for the gravitational wave emission from all core collapse supernova models when simulations are performed with three-dimensional progenitors.

Systematic Study of External Optical Feedback Tolerance in 1300 nm Quantum Dot Lasers

Resilience of 1300nm In(Ga)As/GaAs quantum dot lasers to external optical feedback is systematically investigated from − 10°C to 85 °C. The high-resolution spectral and current-dependent linewidth enhancement factor is measured for all modes in the positive net modal gain region. Complimentary to that, analysis of the free-running and under deployment specific feedback relative intensity noise is discussed in the context of compliance against the IEEE 802.3ah specifications at the full range of temperatures.

Wavelength-tunable multi-point pump semiconductor disk laser based on an intra-cavity transmission grating

We report a wavelength-tunable multi-point pump scheme of the semiconductor disk lasers (SDLs). By designing an external cavity of SDL with an intra-cavity transmission grating, multiple pump gain regions share the same resonator. The effect of the intra-cavity grating on the output laser power, wavelength, and beam quality was investigated. The emission wavelength could be tuned over a bandwidth of ∼18 nm. With multi-point pumping, we achieve the laser output power with almost no loss, and further improvement is limited by the thermal effect. The changes in the beam are due to the mode selectivity by the intra-cavity grating.

Structural Heterogeneity of Chromosome 1q Drives Outcome in Newly Diagnoses Myeloma

Background: The prognostic importance of 1q gain, present in 30% of cases, has led to it being extensively studied and incorporated into prognostic systems. Amplification (>3 copies) of 1q is seen in 10% of cases and has a greater degree of specificity for poor outcome than gain alone. Despite this, there is ongoing debate about its value, likely due to differences in the nature and penetrance of deregulated drivers. To gain insight into this we dissected the structural changes seen at the 1q level and integrated them with expression and clinical data to identify potential drivers and gain insight into progression mechanisms. Methods We analyzed data derived from 1,154 CoMMpass trial patients including 972 NDMM patients with whole exome for mutations, and 752 whole genomes for copy number (CNA), translocations, and complex rearrangements. Using GISTIC 2.0 and PFC we identified hotspots of CNA. This information was analyzed in conjunction with the RNA-seq data derived from 643 patients to determine the aberrant transcriptional landscape of 1q. Results: We identified nine regions of gain (numbered G1 to G9), eight of them being on 1q. Several potential oncogenes such as BCL9 (G2), MCL1 (G3), SLAMF7 (G5), POU2F1 (G6), and BTG2 (G8) lay within these regions of gain. Of note, other previously identified drivers lay outside specific hotspots: ANP32E (306 kb downstream of G3) CKS1B and ADAR1 (1209 kb ( and 1561 kb away from G4, respectively), ATF6 (941 kb from G5), and PBX1 (2313 kb upstream of G6). These data suggest that although important, these hotpots do not drive the entire spectrum of genes upregulated as a consequence of gain 1q. We noted that 302 samples (40%) had at least one gained region with 80% (241/302) having gain of 7-9 regions; 69% (207/302) had gain G2-G9. Each of the gained regions occurred at a similar frequency (G2-G9 range 79-87%) with the exception of G1 located at the sub-telomeric border of 1p seen only in 6% (18/302) of patients. There were 219 cases with gain of G2-G9. These results show two broad groups of gain 1q; whole arm gains and a group with focal gain. Patients with whole arm gain had a worse PFS (HR 1.3 (95% CI 1.01-1.6) and OS (HR 1.6 (95% CI 1.15-2.2) than patients with no 1q gain; the outcome for patients focal events was neutral. Whole arm gains strongly associated with a complex genomic background including with t(4;14) (corr=0.10, BF=1.06), loss of acrocentric chromosomes (del(13q) corr=0.23, BF=118623 and del(14q) corr=0.12, BF=2.9) and other deletions (del(4p) corr=0.11, BF=1.89, del(16p) corr=0.12, BF=2.3) and negatively correlated to trisomies and t(11;14) (corr=0.16, BF=184). Interestingly whole arm gains had significantly shorter telomeres and a higher mean age, and patients with critically short tumor telomeres were over-represented (Corr=0.11, BF=1.2). Common associations with CKS1B gain are mostly found in the whole arm gains group. Amp(1q) was over represented in the whole arm gain group (87%) and associated with the worst outcome (data not shown). Similarly, focal events strongly associated with templated insertion (corr=0.34, BF=6e14), MYC translocation (corr=0.24, BF=3034538), and HRD (corr=0.13, BF=4.9). To address expression changes in focal changes we compared patients with no 1q gain (n=297) with patients with a focal event (n=56); we identified 20 genes of which the majority (n=12) were located on chromosome 1 and related to protein handling. We compared patients with no evidence of 1q gain with patients with a whole arm gain (n= 157); the number of deregulated genes was higher both on 1q and overall (n=585 and n=2409 respectively) suggesting that generalized gene deregulation is part of a more complex genome wide mechanism. Interestingly, 101 were transcription factors and included upregulation of BACH2, NR5A1, MYBL1. GLMP, and E2F2 and downregulation of PAX5, SMAD1, TBX21, SIX4, EGR3, and GF1 most of them being involved in histone methylation, intracellular signaling, and regulation of transcription. Conclusions: Our data add precision by which 1q is associated with an adverse outcome and an aggressive disease phenotype by separating out focal gains, that occur on a favorable background and associate with a good outcome and those with arm-length gains, associated with high-risk disease features, deregulation of multiple transcriptional programs, increased metabolism and aggressive clinical behavior. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Comparative Genomic Hybridization and Transcriptome Sequencing Reveal Genes with Gain in Acute Lymphoblastic Leukemia: JUP Expression Emerges as a Survival-Related Gene.

Acute lymphoblastic leukemia (ALL) in children or adults is characterized by structural and numeric aberrations in chromosomes; these anomalies strongly correlate with prognosis and clinical outcome. Therefore, this work aimed to identify the genes present in chromosomal gain regions found more frequently in patients with acute lymphoblastic leukemia (ALL) and ALL-derived cell lines using comparative genomic hybridization (CGH). In addition, validation of the genes found in these regions was performed utilizing RNAseq from JURKAT, CEM, and SUP-B15 cell lines, as well as expression microarrays derived from a MILE study. Chromosomes with common gain zones that were maintained in six or more samples were 14, 17, and 22, in which a total of 22 genes were identified. From them, NT5C3B, CNP, ACLY, and GNB1L maintained overexpression at the mRNA level in the cell lines and in patients with ALL. It is noteworthy that SALL2 showed very high expression in T-ALL, while JUP was highly expressed in B-ALL lineages. Interestingly, the latter correlated with worse survival in patients. This provided evidence that the measurement of these genes has high potential for clinical utility; however, their expressions should first be evaluated with a sensitive test in a more significant number of patients.

3D simulations of strongly magnetized non-rotating supernovae: explosion dynamics and remnant properties

ABSTRACT We investigate the impact of strong initial magnetic fields in core-collapse supernovae of non-rotating progenitors by simulating the collapse and explosion of a $16.9\, \mathrm{M}_\odot$ star for a strong- and weak-field case assuming a twisted-torus field with initial central field strengths of ${\approx }10^{12}$ and ${\approx }10^{6}\, \mathrm{G}$. The strong-field model has been set up with a view to the fossil-field scenario for magnetar formation and emulates a pre-collapse field configuration that may occur in massive stars formed by a merger. This model undergoes shock revival already $100\, \mathrm{ms}$ after bounce and reaches an explosion energy of $9.3\times 10^{50}\, \mathrm{erg}$ at $310\, \mathrm{ms}$, in contrast to a more delayed and less energetic explosion in the weak-field model. The strong magnetic fields help trigger a neutrino-driven explosion early on, which results in a rapid rise and saturation of the explosion energy. Dynamically, the strong initial field leads to a fast build-up of magnetic fields in the gain region to 40 per cent of kinetic equipartition and also creates sizable pre-shock ram pressure perturbations that are known to be conducive to asymmetric shock expansion. For the strong-field model, we find an extrapolated neutron star kick of ${\approx }350\, \mathrm{km}\, \mathrm{s}^{-1}$, a spin period of ${\approx }70\, \mathrm{ms}$, and no spin-kick alignment. The dipole field strength of the proto-neutron star is $2\times 10^{14}\, \mathrm{G}$ by the end of the simulation with a declining trend. Surprisingly, the surface dipole field in the weak-field model is stronger, which argues against a straightforward connection between pre-collapse fields and the birth magnetic fields of neutron stars.

A new approach to achieving high granularity for silicon diode detectors with impact ionization gain

Low Gain Avalanche Diodes (LGADs) are thin (20-50 μm) silicon diode sensors with modest internal gain (typically 5 to 50) and exceptional time resolution (17 ps to 50 ps). However, the granularity of such devices is limited to the millimeter scale due to the need to include protection structures at the boundaries of the readout pads to avoid premature breakdown due to large local electric fields. Here, we present a new approach – the Deep-Junction LGAD (DJ-LGAD) – that decouples the high-field gain region from the readout plane. This approach is expected to improve the achievable LGAD granularity to the tens-of-micron scale while maintaining direct charge collection on the segmented electrodes.

The generation and observation of pulses with switchable single/dual wavelengths and tunable bandwidth from a SWNT mode-locked Er-doped fiber laser

Mode-locked pulse outputs with switchable single/dual wavelengths and widely tunable spectral bandwidth are demonstrated by fully exploiting multiple soliton formation mechanisms combining single-wall carbon nanotube, intracavity loss tuning and nonlinear polarization rotation. An isolator with single-polarization fiber pigtails is additionally inserted in a ring fiber laser cavity to introduce polarization-dependent loss modulation for gain profile tuning and nonlinear polarization rotation. Mode-locked by a home-made single-wall carbon nanotube saturable absorber, switchable single/dual-wavelength pulses centered in the 1530- or/and 1550-nm gain regions of erbium-doped fiber are experimentally observed by tuning the intracavity loss to tilt the gain profile. Moreover, the spectral bandwidths of single-wavelength pulses centered in the 1530- and 1550 nm regions could be continuously tuned from 2.4 to 4.0 nm, and 2.7 to 9.0 nm, respectively. Such widely tunable spectral bandwidths are attributed to hybrid mode-locked mechanisms combining the nonlinear polarization rotation and single-wall carbon nanotube. Our results give a deep insight into the well-controlled gain profile tuning and provide a relatively simple setup and method to obtain bandwidth-tunable, wavelength-switchable pulse outputs, showing the potential to meet various requirements of ultrafast laser applications.

Electrically pumped quantum-dot lasers grown on 300 mm patterned Si photonic wafers

Monolithic integration of quantum dot (QD) gain materials onto Si photonic platforms via direct epitaxial growth is a promising solution for on-chip light sources. Recent developments have demonstrated superior device reliability in blanket hetero-epitaxy of III–V devices on Si at elevated temperatures. Yet, thick, defect management epi designs prevent vertical light coupling from the gain region to the Si-on-Insulator waveguides. Here, we demonstrate the first electrically pumped QD lasers grown by molecular beam epitaxy on a 300 mm patterned (001) Si wafer with a butt-coupled configuration. Unique growth and fabrication challenges imposed by the template architecture have been resolved, contributing to continuous wave lasing to 60 °C and a maximum double-side output power of 126.6 mW at 20 °C with a double-side wall-plug efficiency of 8.6%. The potential for robust on-chip laser operation and efficient low-loss light coupling to Si photonic circuits makes this heteroepitaxial integration platform on Si promising for scalable and low-cost mass production.

(Invited) Achieving High-Power Single-Mode Operation in Vertical-Cavity Surface-Emitting Lasers Via Scalable, Higher-Order Mode Suppression Techniques

Achieving high-power single-mode operation in Vertical-Cavity Surface-Emitting Lasers (VCSELs) has received renewed interest because of applications that span facial recognition and 3D imaging in mobile telephones, Light Detection and Ranging (LiDAR) for autonomous vehicles, and Pulse Amplitude Modulation (PAM-4) for high-speed (>100 Gbps) data transmission within data centers. A key challenge with oxide-confined VCSELs is that the strong refractive index contrast between the oxidized ~AlAs aperture and surrounding AlGaAs layers combined with the oxide aperture size create a photonic cavity that fundamentally supports multiple transverse modes. When the size of the aperture is reduced to create a single-mode cavity, the output power is limited by the electrically pumped gain region within the aperture. There is thus a fundamental trade-off between size and power which manifests itself in a limited capability to simultaneously achieve high power and single mode operation. Various methods have been employed by groups working on VCSELs to overcome this limitation. Neglecting external cavity methods which are fundamentally not scalable, the most promising results have been achieved by groups using etched surface relief where a pattern is etched in the top layer or layers to change the standing wave pattern in the cavity and reduce modal gain by lowering the magnitude of the electric field in regions overlapping with the quantum wells, which provide laser gain. A downside of this approach is that material is removed, impacting the uniformity of current injection across the area of the device. A key question of interest is therefore how to achieve mode suppression in large area devices in a way that does not impact current injection. In this presentation, novel methods for mode control that rely on spatial variation of modal gain across the area of the VCSEL aperture will be discussed, and results on high-power single-mode operations of VCSELs will be presented. Two distinct mode control methods will be reviewed. The first method of mode control uses deposited optical coatings on the top surface of the VCSEL to spatially modify the electric field standing wave in the quantum well heterostructure region. Through patterning the coating in either a pillar or anulus, specific modes can be suppressed by selectively changing the gain available for those modes. These filters have been made using both SiO2/TiO2 stacks and alternatively a single layer of silicon. The capability to pattern these layers in a wafer-scale process makes this method attractive for volume manufacturing. The second method of mode control utilizes impurity-induced layer disordering via patterned diffusion of Zn to selectively intermix Distributed Bragg Reflector (DBR) layers, thereby creating a top laser mirror whose reflectivity varies spatially across the aperture. Designing the diffused region to maximize overlap with high-order modes while minimizing overlap with the fundamental mode provides mode suppression and enhanced single-mode power. An added benefit of this approach is a reduction in resistance through the device top DBR layers brought about by the higher p-doping level in the Zn-diffused regions, minimizing Ohmic losses and heat generation. Through the use of strain control in the diffusion mask, diffusion front shape is also shown to be controllable in a way that can be used to minimize the impact of the diffused region on fundamental mode reflectivity. Tensile and compressive strain of diffusion masks are shown to have differing effects on vertical (into the device) versus lateral (across the area of the device under the mask) diffusion, allowing more precise spatial control of reflectivity. Using these methods, single-mode output powers in excess of 10 mW have been demonstrated, with side-mode suppression ratios in excess of 30 dB. These results will be discussed, as well as further work to enhance VCSEL performance. Figure 1

Generation of Three-Mode Entanglement Based on Parametric Amplifiers Using Quantum Entanglement Swapping

Quantum entanglement swapping is one of the most promising quantum techniques to create or manipulate large-scale multi-mode entanglement between two distant quantum entangled systems. In this work, a scheme for the generation of three-mode entanglement based on parametric amplifiers using quantum entanglement swapping has been proposed. The newly generated three-mode entanglement is always present in the whole power gain region from parametric amplifiers and its dependence on transmission loss and feedforward gain is also investigated. In addition, the effects of power gain, transmission loss, and feedforward gain on the two-mode entanglement of the three pairs in the newly generated three-mode entanglement have also been analysed in detail. The results presented here may find some practical applications in quantum secure communication.

Advances in Energy‐Level Systems of Organic Lasers

AbstractOrganic gain materials, with the merit of abundant excited‐state processes with large stimulated emission cross‐section, show considerable potential in lasers. The abundant excited‐state processes provide excellent platform for the construction of various forms of energy‐level systems, based on which the efficient population inversion and the tailorable gain region are supported. Herein, the development of organic lasers with distinctive energy‐level systems is summarized according to the classification of excited‐state gain processes including singlet quasi‐four‐level transition, energy transfer, excimer, charge transfer (CT), excited‐state intramolecular proton transfer (ESIPT), and some other novel photophysical processes, giving deep insight into the inherent relationship between energy‐level systems and laser action. Finally, the challenges and perspectives for the future development are presented, hopefully to offer valuable enlightenment for the further optimization of energy‐level systems toward high‐gain organic lasers including electrically pumped organic lasers.

Magnetic support for neutrino-driven explosion of 3D non-rotating core-collapse supernova models

ABSTRACT The impact of the magnetic field on post-bounce supernova dynamics of non-rotating stellar cores is studied by performing 3D magnetohydrodynamics simulations with spectral neutrino transport. The explodability of strongly and weakly magnetized models of 20 and 27 M⊙ pre-supernova progenitors are compared. We find that although the efficiency for the conversion of the neutrino heating into turbulent energy including magnetic fields in the gain region is not significantly different between the strong and weak field models, the amplified magnetic field due to the neutrino-driven convection on large hot bubbles just behind stalled shock results in a faster and more energetic explosion in the strongly magnetized models. In addition, by comparing the difference between the 2nd- and 5th-order spatial accuracy of the simulation in the strong field model for 27 M⊙ progenitor, we also find that the higher order accuracy in space is beneficial to the explosion because it enhances the growth of neutrino-driven convection in the gain region. Based on our results of core-collapse supernova simulations for the non-rotating model, a new possibility for the origin of the magnetic field of the protoneutron star (PNS) is proposed. The magnetic field is accumulated and amplified to magnetar level, that is, $\mathcal {O}(10^{14})$ G, in the convectively stable shell near the PNS surface.

Additively manufactured transparent ceramic thin disk gain medium

A novel type of Yb:YAG transparent ceramic thin disk laser amplifier is demonstrated, based on fabricating a composite gain element with a paraboloidal interface between gain and no-gain regions and employing side-pumping of the thin disk. The pump-induced gain and the impact of amplified spontaneous emission on the achievable inversion are reported.

Boosting Jittering Jets by Neutrino Heating in Core Collapse Supernovae

I estimate the energy that neutrino heating adds to the outflow that jets induce in the collapsing core material in core collapse supernovae (CCSNe), and find that this energy crudely doubles the energy that the jets deposit into the outer core. I consider the jittering jets explosion mechanism where there are several stochastic jet-launching episodes, each lasting for about 0.01–0.1 s. The collapsing core material passes through the stalled shock at about 100 km and then slowly flows onto the proto-neutron star (NS). I assume that the proto-NS launches jittering jets, and that the jets break out from the stalled shock. I examine the boosting process by which the high-pressure gas inside the stalled shock, the gain region material, expands alongside the jets and does work on the material that the jets shock, the cocoon. This work is crudely equal to the energy that the original jets carry. I argue that the coupling between instabilities, stochastic rotation, magnetic fields, and jittering jets leads to most CCSN explosions. In other cases, the pre-collapse core is rapidly rotating and therefore ordered rotation replaces stochastic rotation and fixed jets replace jittering jets.

The Silicon Electron Multiplier sensor

The Silicon Electron Multiplier (SiEM) is a novel sensor concept for minimum ionising particle (MIP) detection which uses internal gain and fine pitch to achieve excellent temporal and spatial resolution. In contrast to sensors where the gain region is induced by doping (LGADs, APDs, SPADs), amplification in the SiEM is achieved by applying an electric potential difference in a composite electrode structure embedded within the silicon bulk using MEMS fabrication techniques. Since no gain-layer deactivation is expected with radiation damage, such a structure is expected to withstand fluences of up to 1016 neq/cm2. Various geometries and biasing configurations are studied, within the boundaries imposed by the fabrication process being considered. The effective gain, the field in the sensor, the leakage current and breakdown conditions are studied for cell sizes in the range of 6–15µm. Simulations show that gains in excess of 10 can be achieved, and studies of the time structure of the induced signals from a charge cloud deposited in the middle of the sensor show that time resolutions similar to other sensors with internal gain can be expected. Plans for the manufacture of a proof-of-concept sensor and for its subsequent characterisation are discussed.