A Tektronix modern digital oscilloscope, which measures the output, a periodic pulse sequence, generated by an industrial mode-locked laser. Such a laser produces ultrashort pulses spaced in time at equal intervals. The response time of the semiconductor diode detector (nanosecond) is much slower than the individual optical pulse length (femtosecond), so the displayed pulses are longer than the actual optical pulses. A typical diode "ringing" is apparent between the pulses on the display. Such a measurement is often used to evaluate the stability and quality of mode-locking. Limited depth of field; oscilloscope brand name not visible.