They also show the same increase for peak amplitude at constant pulse width and increasing repetition rate (see Figure ). The increasing peak amplitude can be attributed to the increasing duty cycle and thus increasing energy deposited in the absorber. The peak amplitude at the highest tested frequency (1231 kHz) deviates from the trend seen for the other frequency but follows the FWHM trend (see Figure ). This is due to the fact that at this setting a duty cycle of 12.3 % had been reached which goes beyond the specifications of the laser used. In this regime the EC-QCLs control circuit will skip every other pulse so as to stay within the maximum duty cycle specifications of the device and avoid damage, leading to a 50 % reduction in peak amplitude. The FWHM is not affected by this.