This burner works with oxygen and hydrogen gained from electrical splitting water in its components. The green flame results from combining the gas with a  admixture that gives the soldered surface slight protection against oxydation and lowers the flame-temperature to approx. 1700 degree celsius.

Hard soldering in juwel sector is done with a temperature of the workpiece between 450 and 800 degree Celsius (gold) and even up to 1200 - 1400 degree (platinum).
The temperature at which the solder becomes liquid depends on the admixtures in the solder. (metals with low flowingpoint)

There are also bigger versions of burners, using propan / hydrogen with oxygene or propan with the surrounding air, often burners shown below are used, the necessary oxygene comes from blowing trough a mouthpiece in a hose which is connected with the burner.
Hoses and mouthpiece are not shown below.

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