Catalysts and methods for their manufacture and use for the synthesis of dimethyl ether from syngas are disclosed. The triangular wave has a cycle duration obtained by dividing the cycle duration of the generator by product of 3 and odd number, a crest having a level higher than the sine wave at a timing of each first period, and a trough having a level lower than the sine wave at a timing of each second period. The change of the absorption coefficient in the modulator section results in a change in the Q-factor of the laser, and consequently the lasing threshold and output power. The hot-air supplying module has an air-blowing impeller and a heating element.