RESUMO
Temporal and spatial shaping of laser beams is common in laser micromachining applications to improve quality and throughput. However, dynamic beam shaping (DBS) of ultrashort, high-power pulses at rates of hundreds of kHz has been challenging. Achieving this allows for full synchronization of the beam shape with high repetition rates, high-power lasers with zero delay time. Such speeds must manipulate the beam shape at a rate that matches the nanosecond to microsecond process dynamics present in laser ablation. In this work, we present a novel design capable of alternating spatial and temporal beam shapes at repetition rates up to 330 kHz for conventional spatial profiles and temporal shaping at nanosecond timescales. Our method utilizes a unique multi-aperture diffractive optical element combined with two acousto-optical deflectors. These high damage threshold elements allow the proposed method to be easily adapted for high power ultrashort lasers at various wavelengths. Moreover, due to the combination of the elements mentioned, no realignment or mechanical movements are required, allowing for high consistency of quality for high throughput applications.
RESUMO
In mammals, cellular identity is defined through strict regulation of chromatin modifications and DNA methylation that control gene expression. Methylation of cytosines at CpG sites in the genome is mainly associated with suppression; however, the reason for enhancer-specific methylation is not fully understood. We used sequential ChIP-bisulfite-sequencing for H3K4me1 and H3K27ac histone marks. By collecting data from the same genomic region, we identified enhancers differentially methylated between these two marks. We observed a global gain of CpG methylation primarily in H3K4me1-marked nucleosomes during mouse embryonic stem cell differentiation. This gain occurred largely in enhancer regions that regulate genes critical for differentiation. The higher levels of DNA methylation in H3K4me1- versus H3K27ac-marked enhancers, despite it being the same genomic region, indicates cellular heterogeneity of enhancer states. Analysis of single-cell RNA-seq profiles demonstrated that this heterogeneity correlates with gene expression during differentiation. Furthermore, heterogeneity of enhancer methylation correlates with transcription start site methylation. Our results provide insights into enhancer-based functional variation in complex biological systems.
Assuntos
Diferenciação Celular/genética , Cromatina/genética , Metilação de DNA/genética , Elementos Facilitadores Genéticos/genética , Animais , Humanos , Camundongos , Células-Tronco Embrionárias Murinas , Nucleossomos/genética , Regiões Promotoras Genéticas/genética , RNA-Seq , Análise de Célula Única , Sítio de Iniciação de TranscriçãoRESUMO
In this work, we present the advantages of driving a multichannel acousto-optical deflector (AOD) with a digitally synthesized multifrequency RF signal. We demonstrate a significant bandwidth broadening of â¼40% by providing well-tuned phase control of the array transducers. Moreover, using a multifrequency, complex signal, we manage to suppress the harmonic deflections and return most of the spurious energy to the main beam. This method allows us to operate the AOD with more than an octave of bandwidth with negligible spurious energy going to the harmonic beams and a total bandwidth broadening of over 70%.
