Acousto-Optic Modulation in Ambient Air

Control over intensity, shape, direction and phase of coherent light is a cornerstone of 20 photonics. Modern laser optics, however, frequently demands parameter regimes where either the wavelength or the optical power restricts control e.g. due to absorption or damage. Limitations are imposed by the properties of solid media, upon which most photonic control schemes rely. We propose to circumvent these limitations using gas media tailored by high-intensity ultrasound waves. We demonstrate a first implementation of this approach by modulating ultrashort laser 25 pulses using ultrasound waves in ambient air, entirely omitting transmissive solid media. At peak powers of 20 GW exceeding the limits of solid-based acousto-optical modulation by about three orders of magnitude, we reach a diffraction efficiency greater than 50% while preserving excellent beam quality. Our results open a route towards versatile gas-phase Sono-Photonic methods, i.e. gas-based photonic systems controlled by sonic waves.Comment: 20 pages, including 11 pages of main text and 9 pages of supplementary text, 3 figures, 3 supplemtary figures, 1 supplementary tabl

Exploring Aboriginal People\u27s connection to country to strengthen human-nature theoretical perspectives

Purpose Aboriginal people across Australia have diverse practices, beliefs and knowledges based on thousands of generations of managing and protecting their lands (Country). The intimate relationship Aboriginal people have with their Country is explored in this chapter because such knowledge is important for building insight into the relationship between social and ecological systems. Often in research Aboriginal views have been marginalised from discussions focused on their lands to the detriment of ecosystems and human health. This chapter aims to understand if such marginalisation is evident in Western human–nature relationship discourses.Approach This chapter provides a critical literature review which examines whether Aboriginal people’s diverse understanding of their ecosystems have been incorporated into human–nature theories using the biophilia hypothesis as a starting point. Other concepts explored include solastalgia, topophilia and place.Findings Critiques of these terminologies in the context of Aboriginal people’s connection to Country are limited but such incorporation is viewed in the chapter as a possible mechanism for better understanding human’s connection to nature. The review identified that Aboriginal people’s relationship to Country seems to be underrepresented in the human–nature theory literature.Value This chapter emphasises that the integration of Aboriginal perspectives into research, ecological management and policy can provide better insight into the interrelationships between social and ecological systems

Split-Cre Complementation Indicates Coincident Activity of Different Genes In Vivo

Cre/LoxP recombination is the gold standard for conditional gene regulation in mice in vivo. However, promoters driving the expression of Cre recombinase are often active in a wide range of cell types and therefore unsuited to target more specific subsets of cells. To overcome this limitation, we designed inactive “split-Cre” fragments that regain Cre activity when overlapping co-expression is controlled by two different promoters. Using transgenic mice and virus-mediated expression of split-Cre, we show that efficient reporter gene activation is achieved in vivo. In the brain of transgenic mice, we genetically defined a subgroup of glial progenitor cells in which the Plp1- and the Gfap-promoter are simultaneously active, giving rise to both astrocytes and NG2-positive glia. Similarly, a subset of interneurons was labelled after viral transfection using Gad67- and Cck1 promoters to express split-Cre. Thus, split-Cre mediated genomic recombination constitutes a powerful spatial and temporal coincidence detector for in vivo targeting

Intravenous alteplase for stroke with unknown time of onset guided by advanced imaging: systematic review and meta-analysis of individual patient data

Background: Patients who have had a stroke with unknown time of onset have been previously excluded from thrombolysis. We aimed to establish whether intravenous alteplase is safe and effective in such patients when salvageable tissue has been identified with imaging biomarkers. Methods: We did a systematic review and meta-analysis of individual patient data for trials published before Sept 21, 2020. Randomised trials of intravenous alteplase versus standard of care or placebo in adults with stroke with unknown time of onset with perfusion-diffusion MRI, perfusion CT, or MRI with diffusion weighted imaging-fluid attenuated inversion recovery (DWI-FLAIR) mismatch were eligible. The primary outcome was favourable functional outcome (score of 0–1 on the modified Rankin Scale [mRS]) at 90 days indicating no disability using an unconditional mixed-effect logistic-regression model fitted to estimate the treatment effect. Secondary outcomes were mRS shift towards a better functional outcome and independent outcome (mRS 0–2) at 90 days. Safety outcomes included death, severe disability or death (mRS score 4–6), and symptomatic intracranial haemorrhage. This study is registered with PROSPERO, CRD42020166903. Findings: Of 249 identified abstracts, four trials met our eligibility criteria for inclusion: WAKE-UP, EXTEND, THAWS, and ECASS-4. The four trials provided individual patient data for 843 individuals, of whom 429 (51%) were assigned to alteplase and 414 (49%) to placebo or standard care. A favourable outcome occurred in 199 (47%) of 420 patients with alteplase and in 160 (39%) of 409 patients among controls (adjusted odds ratio [OR] 1·49 [95% CI 1·10–2·03]; p=0·011), with low heterogeneity across studies (I2=27%). Alteplase was associated with a significant shift towards better functional outcome (adjusted common OR 1·38 [95% CI 1·05–1·80]; p=0·019), and a higher odds of independent outcome (adjusted OR 1·50 [1·06–2·12]; p=0·022). In the alteplase group, 90 (21%) patients were severely disabled or died (mRS score 4–6), compared with 102 (25%) patients in the control group (adjusted OR 0·76 [0·52–1·11]; p=0·15). 27 (6%) patients died in the alteplase group and 14 (3%) patients died among controls (adjusted OR 2·06 [1·03–4·09]; p=0·040). The prevalence of symptomatic intracranial haemorrhage was higher in the alteplase group than among controls (11 [3%] vs two [<1%], adjusted OR 5·58 [1·22–25·50]; p=0·024). Interpretation: In patients who have had a stroke with unknown time of onset with a DWI-FLAIR or perfusion mismatch, intravenous alteplase resulted in better functional outcome at 90 days than placebo or standard care. A net benefit was observed for all functional outcomes despite an increased risk of symptomatic intracranial haemorrhage. Although there were more deaths with alteplase than placebo, there were fewer cases of severe disability or death. Funding: None

Detailed investigation of absorption, emission and gain in Yb:YLF in the 78-300 K range

We present spectroscopic measurements focusing on a detailed investigation oftemperature dependence of absorption, emission and gain in the uniaxial Yb:YLF laser gainmedium. Measurements are carried out in the 78–300 K range, but we especially targeted ourattention to the 78–150 K interval, which is the desired working range of liquid nitrogen cooledcryogenic Yb:YLF lasers/amplifiers. A tunable (770–1110 nm) Cr:LiSAF laser with around100 mW continuous-wave output power and sub-0.2 nm bandwidth is used as an excitationsource. The average power of the Cr:LiSAF laser is low enough to prevent heating of the sample,and its spectral flux (W/nm) is high enough to enable large signal-to-noise ratio measurements.Measured absorption data is used to cross-check the validity of the emission measurements, whilethe measured temperature dependent small-signal gain profile provided a second independentconfirmation. The acquired absorption cross section curves match the previous literature quitewell, whereas the measured strength of c-axis emission is stronger than some of the earlier reports.Direct measurements of small signal gain confirmed the emission cross section data, where singlepass gain values above 50 have been measured for the 995 nm transition of E//c axis at 78 K. Wefurther provide simple analytic formulas for the measured temperature dependence of absorptionand emission cross section. We hope the presented results to be useful for the development ofnext generation of cryogenic Yb:YLF laser and amplifier systems

Error analysis of contactless optical temperature probing methods for cryogenic Yb:YAG

In this work, we have investigated six diferent in situ optical contactless temperature probing methods for cryogenicYb:YAG systems. All the methods are based on variation of fuorescence spectra with temperature, and they either look atthe width of the emission line, the ratio of the emission intensity at diferent wavelengths and to the overall spectral changeat selected wavelength intervals. We have shown that, for Yb:YAG crystal with homogeneous temperature distribution, onecan perform real-time contactless optical temperature measurements with a±1 K accuracy in the 78–300 K range. We havefurther tested the methods in measuring the average temperature of Yb:YAG rods at up to 500 W absorbed pump powerlevel. We have seen that, a real-time temperature measurement accuracy of±5 K is feasible in both lasing and non-lasingsituations for estimating the average temperature of crystals under nonhomogeneous thermal load. The techniques are quitevaluable in evaluating the bonding quality of Yb:YAG crystals in cryogenic systems. Moreover, the real-time temperatureinformation provides feedback on parameters like cavity alignment status and extraction efciency to the laser engineerswhile optimizing the syste

70W, 1MHz, sub-50fs Yb-Doped Fiber Laser System for High Harmonic Generation

We report the development of an ultra-fast, high repetition rate, high-power fiber laser system at 1 μm for high harmonic generation (HHG) to be deployed in a Tr-ARPES setup [1], that is currently served by a lower repetition rate Ti:Sapphire system. HHG is based on a non-linear interaction between intense laser pulses and a gaseous medium leading to the generation of short, coherent extreme UV (XUV) pulses [1]. The laser system required for efficient HHG should provide high-energy ultrashort pulses. Moreover, Tr-ARPES based on the detection of weak photo electron pulses requires a high repetition rate source [2] to maximize signal while minimizing acquisition times. Therefore, the HHG laser system with a high pulse repetition rate and peak power is necessary

Eight-pass Yb:YLF cryogenic amplifier generating 305-mJ pulses

We report record output pulse energies from a cryogenic 8-pass Yb:YLF amplifier system operating at 10 Hz repetition rate. When seeded with 20-mJ, 1-ns stretched pulses, the amplifier produced output pulses with 305 mJ of energy at 1018.5 nm with a spectral width supporting sub-ps pulse-duration. The output beam profile was quite symmetric and had a measured beam quality factor (M$^2$) of ∼1.45. To achieve this performance, the diameter of the beam inside the gain element is gradually increased via an adjustable telescope from around 4.6 mm to 6.2 mm. This enables adjustment of the fluence to a moderate value in subsequent passes: high enough for efficient extraction and low enough to prevent laser induced damage. To our knowledge, this is the highest pulse energy reported from cryogenically cooled Yb:YLF amplifiers to date. Further scaling in peak power and repetition rate is anticipated in future work

100mJ, 100W Cryogenically Cooled Yb:YLF Laser

We present the generation of 100 mJ sub-ps pulses at a 1 kHz repetition rate (100 W average power) by chirped-pulse amplification in a diode-pumped Yb:YLF laser. The laser consists of cryogenically-cooled 78K, regenerative, and 8-pass booster amplifiers seeded by an all-fiber front end. The output pulses are compressed to 980 fs in a single grating Treacy compressor with a throughput of 89%. The laser will be applied to multicycle THz generation and pump high-average power parametric attosecond amplifier