什么是最大－20DB带宽？

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问题问答题简答题

什么是最大－20DB带宽？

答案

参考答案：

单纵模激光器主要能量集中在主模，其光谱宽度以其主模的最大峰值功率下跌－20DB时最大带宽来定义的，该带宽为最大－20DB带宽。

阅读理解

阅读短文，在家谱图中填上名字

This is my family tree. My name is Jack. I’m English. I have a big family. My wife Allen is a teacher.

We have two children. Tom is my son. Linda is my daughter. They are students in No. 2 Middle

School. My father’s name is Jeff. My mother’s name is Grace. They are at home. Bill is my brother. He

is a worker. Lancy is my wife’s sister. She is a doctor. My wife’s mother’s name is Sue. Her father’s

name is Harry. They are old, too.

1._______ 2._______ 3._______ 4._______ 5._______ 6._______ 7._______

单项选择题

上海《实施办法》规定了“直接面向公众服务的工作人员的普通话水平达到三级甲等以上，其中广播员、解说员、话务员等特殊岗位人员的普通话水平达到（）以上。”

A.二级甲等

B.二级乙等

C.三级甲等