Method and apparatus for measuring ultrashort optical pulses

A method for measuring ultrashort optical pulses which are repetitive pulses at a fixed time interval comprising the steps of:

• splitting a light beam to be measured into two beams;
• recombining said two split light beams while providing relative path length differences therebetween;
• doubling said recombined beam to form a second-harmonic bean;
• transforming intensities of a fundamental wave and said second-harmonic beam into electric signals proportional thereto;
• recording changes in intensities of the fundamental wave and the second-harmonic light which are caused by said difference in said relative light path length;
• and
• performing a Fourier-analysis on the recorded data to obtain the intensity shape and phase shape of the measured pulse.

A method for measuring ultrashort optical pulses, which are repetitive pulses at a fixed time interval, comprising the steps of:

• splitting a light beam to be measured into two beams;
• directing the two beams through different paths to provide a relative path length difference therebetween;
• recombining said two beams;
• doubling said recombined beam to produce a second-harmonic beam;
• determining data indicative of the changes in the intensity of the second-harmonic light caused by said relative path length difference;
• Fourier-analysing the data thus obtained to obtain three spectra distributed at an interval equivalent to a frequency of an interference fringe of a fundamental wave;
• Fourier-transforming the square root of a first spectrum, closest to the zero frequency among said three spectra, in order to reconstruct the intensity shape of the object pulses;
• and
• reconstructing the phase of the object pulses by performing iterative calculations using a square root of the spectrum close to the frequency equivalent to double said interference fringe frequency of said fundamental wave and said reconstructed intensity shape.

A method for measuring ultrashort optical pulses, which are repetitive pulses at a fixed time interval, comprising the steps of:

• splitting a light beam to be measured into two beams;
• directing the two beams through different paths to provide a relative path length difference therebetween;
• recombining said two beams;
• doubling said recombined beam to form a second-harmonic beam;
• low pass filtering said voltage to extract a frequency component near DC;
• high pass filtering said voltage to extract a high pass frequency component near a measuring frequency equivalent to two times of an interference fringe frequency of the fundamental wave .omega..sub.0 ;
• measuring said high pass frequency component;
• recording thus obtained data about said frequency component near DC and said high pass frequency component in a time sequence while varying said relative path length difference at a constant rate;
• Fourier-analyzing the data on said component near DC among the pair of sampled data trains;
• performing an inverse Fourier-transformation on the square root of the spectrum to reconstruct the intensity shape of the measured optical pulse;
• Fourier-analyzing the data on the AC voltage;
• and
• reconstructing the phase of the measured optical pulse from the square root of the obtained spectrum and the reconstructed intensity shape by iterative computation.

An apparatus for measuring ultrashort optical pulses, which are repetitive pulses at a fixed time interval, comprising:

• a Michelson inferometer, receiving a light beam to be measured and producing a recombined output beam;
• crystal means for doubling said recombined output to produce a second-harmonic beam;
• fringe extraction means for processing said recombined beam to obtain spectra distributed at an interval of an interference fringe of a fundamental wave .omega..sub.0 ;
• and
• filter means for obtaining a spectrum near DC and a spectrum near 2.omega..sub.0 from among said spectra;
• and
• means for calculating an intensity shape I(t) from said spectrum near DC and calculating a pulse phase from said spectrum near 2.omega..sub.0.

An apparatus for measuring ultrashort optical pulses which are repetitive pulses at a fixed time interval comprising:

• means for splitting a light beam to be measured into two beams;
• means for recombining said two split light beams while providing relative path length differences therebetween;
• means for doubling said recombined beam to form a second-harmonic beam;
• means for transforming intensities of a fundamental wave and said second-harmonic beam into electric signals proportional thereto;
• and
• means for recording changes in intensities of the fundamental wave and the second-harmonic light which are caused by said difference in said relative light path length and performing a Fourier-analysis on the recorded data to obtain the intensity shape and phase shape of the measured pulse.

An apparatus for measuring ultrashort optical pulses, which are repetitive pulses at a fixed time interval, comprising:

• means for splitting a light beam to be measure into two beams;
• means for directing the two beams through different paths to provide a relative path length difference therebetween;
• means for recombining said two beams;
• means for doubling said recombined beam to produce a second-harmonic beam;
• and
• calculating means for (1) determining data indicative of the changes in the intensity of the second-harmonic light caused by said relative path length difference, (2) Fourier-analyzing the data thus obtained to obtain three spectra distributed at an interval equivalent to a frequency of an interference fringe of a fundamental wave, (3) Fourier-transforming the square root of a first spectrum, closest to the zero frequency among said three spectra, in order to reconstruct the intensity shape of the object pulses, and (4) reconstructing the phase of the object pulses by performing iterative calculations using a square root of the spectrum close to the frequency equivalent to double said interference fringe frequency of said fundamental wave and said reconstructed intensity shape.