How to specify font type in a text field using pdfcairo?

[Kirzhanov]

This works fine with "postscript enhanced" terminal:

set xlabel "Regular font {/Italic italic font}"

I would like to use pdfcairo instead of postscript. Now my "set
terminal" statement looks like this:

set terminal pdfcairo enhanced mono dashed linewidth 2 size 17cm,
20cm font "Helvetica,8"

I also tried FreeSerif, Arial and Times instead of Helvetica. But I
could not make the set xlabel statement

set xlabel "Regular font {/Italic italic font}"

to display a part of label with italic font.

By the way, why the definition of the font in 'set term' statement
like 'set term ... postscript ... size 17cm,20cm "Helvetica,8"'
causes much smaller glyphs in output (EPS file) than in statement 'set
term ... pdfcairo ... size 17cm,20cm "Helvetica,8"' (the output is
PDF in the last case)?

Yours,