Optical pulse pair generator, light detection device, and light detection method

A method of detecting light of a molecular vibration using a light detection device including a laser light source configured to generate a light source pulse beam, a splitter section configured to split the light source pulse beam into three by splitting into an excitation pulse beam, and a first probe pulse beam and a second probe pulse beam that both have a predetermined waveform, a first shaping section configured to shape the first probe pulse beam by shaping into the predetermined waveform and setting a central frequency, a second shaping section configured to shape the second probe pulse beam by shaping into the predetermined waveform, a modulation section configured to phase modulate the second probe pulse beam, a multiplexing section configured to multiplex the excitation pulse beam, the first probe pulse beam, and the second probe pulse beam so as to generate a multiplexed beam, and an illumination section configured to illuminate a sample with the multiplexed beam, the light detection method comprising:

• setting a difference between a central wavelength of the first probe pulse beam and a central wavelength of the second probe pulse beam so as to be separated by a wavelength difference corresponding to a frequency of the molecular vibration;
• setting the predetermined waveforms so as to be substantially the same asymmetric waveforms having a fall time that is longer than a rise time;
• temporally superimposing the first probe pulse beam and the second probe pulse beam and delaying the first probe pulse beam and the second probe pulse beam relative to the excitation pulse beam by a predetermined delay time;
• and
• by a detection section, detecting a molecular vibration excited by the excitation pulse beam when the multiplexed beam is illuminating the sample by employing heterodyne interference due to the first probe pulse beam and the second probe pulse beam.