Porous glass matrix producing burner and porous glass matrix producing method

A porous glass matrix producing method, involving use of a porous glass matrix producing burner comprising:

• a plurality of annular gas jetting openings that are concentrically arranged outward from a glass material gas jetting port having a center axis;
• and one line or plural lines of small-diameter gas jetting ports that are arranged concentrically with respect to the center axis in any of the plurality of gas jetting openings other than a most outward gas jetting opening, axis lines of those small-diameter gas jetting ports that are located on a same circumference among the small-diameter gas jetting ports having a crossing point on an extended line of the center axis, the method comprising:
• supplying a combustible gas and a combustion improving gas to the porous glass matrix producing burner;
• and
• depositing glass particles on a starting matrix of a porous glass matrix by spraying a flame including the glass particles to the starting matrix from the porous glass matrix producing burner while reciprocating the starting matrix and the porous glass matrix producing burner with respect to each other,
• wherein the most outward gas jetting opening of the plurality of gas jetting openings is clogged by a clogging member, and one line or plural lines of gas jetting holes are provided in the clogging member concentrically with respect to the center axis.