RESUMO
Continuously and widely tunable lasers, actively stabilized on a frequency reference, are broadly employed in atomic, molecular, and optical (AMO) physics. The frequency-stabilized optical frequency comb (OFC) provides a novel optical frequency reference, with a broadband spectrum that meets the requirement of laser frequency stabilization. Therefore, we demonstrate a frequency-stabilized and precisely tunable laser system based on it. In this scheme, the laser frequency locked to the OFC is driven to jump over the ambiguity zones, which blocks the wide tuning of the locked laser, and tuned until the mode hopping happens with the always-activated feedback loop. Meanwhile, we compensate the gap of the frequency jump with a synchronized acoustic optical modulator to ensure the continuity. This scheme is applied to an external cavity diode laser (ECDL), and we achieve tuning at a rate of about 7 GHz/s, with some readily available commercial electronics. Furthermore, we tune the frequency-stabilized laser only with the feedback of diode current, and its average tuning speed can exceed 100 GHz/s. Due to the resource-efficient configuration and the simplicity of completion, this scheme can be referenced and can find wide applications in AMO experiments.
RESUMO
Recently, mesenchymal stem cells (MSCs) have been one of the target cells of gene engineering. To construct the lentiviral (LV) vectors carrying the brain-derived neurotrophic factor (Bdnf) gene, the rat mesenchymal stem cells (rMSCs) were infected and finally the Bdnf gene-modified rMSCs was obtained. The CDS region of the rat Bdnf gene was obtained with reverse transcriptase-polymerase chain reaction (RT-PCR), and the transfer plasmid (PNL-BDNF-IRES2-EGFP) of the LV vector was constructed. The three plasmids of LV vector: PNL-BDNF-IRES2-EGFP, HELPER, and VSVG were cotransfected to 293T cells to produce the LV vectors, which enabled the coexpression of the Bdnf gene and the enhanced green fluorescent protein (Egfp) gene. rMSCs were separated from the bone marrow of 2-month-old F344 rats, cultured in vitro, and identified. rMSCs were infected by the LV vectors that were produced already and were identified with fluorescent microscope, RT-PCR, immunocytochemical staining, and western blot. The result of sequencing showed that the sequence of the cloned Bdnf gene was consistent with that reported in the GenBank. The PNL-BDNF-IRES2-EGFP plasmid that was identified showed the correct sequence. After the 3 plasmids of LV vectors were cotransfected to the 293T cells, considerable green fluorescence in 293T cells was observed under the fluorescent microscope; the supernatant was collected and concentrated using ultracentrifugation, and the titer of the replication-defective LV vector particles measured was found to be 6.7 x 10(7) TU/mL. After the constructed LV vectors infected the rMSCs, the results obtained using RT-PCR, immunocytochemical staining, and western blot showed that the expression of BDNF in the Bdnf-rMSCs group (experimental group, EG) was significantly higher than that in the PNL-IRES2-EGFP-rMSCs group (mock group, MG) and the rMSCs group (control group, CG) at both mRNA and protein levels. LV vectors carrying the Bdnf gene were constructed successfully. The Bdnf gene-modified rMSCs could express BDNF to a higher degree. This greatly facilitates the next step in the study, such as the long period of therapeutic observation of cerebral ischemia with Bdnf gene-modified rMSCs.