For the Purpose of studying the mechanism of lowering breakdown voltage in the new type（Tian Jin type） He-Ne Laser

three kinds of tubes （the common type

the new type I and new type I） were made and breakdown voltage measurements were performed in several gases （He

Ne

He-Ne

Ar

Kr

H2

and N2）. The experimental results show that the breakdown voltage for the new types is fairly lower than the common one

but this effect occurs only within a definite range of gas pressure. As the pressure increases to a certain value P0

which depends on what gas is used

the lowering effects vanish. A theoretical explanation for the experimental results is given.