Method for measuring an optical length of light path and a laser interferometer for carrying same into effect

A method of measuring the optical length of a preset light path interval, said method comprising the following consecutive steps:

• building up an original light beam in the following way:
• creating a beam of coherent light;
• separating two colinear components from said beam, said two colinear components including a first colinear component and a second colinear components, having two respective independent polarizations;
• offsetting the light frequency of one of said components from the other component;
• presetting a light path interval;
• forming a first interfering light beam as follows:
• separating a part of the light from said original beam of coherent light which comprises said first coliner component and said second colinear component with independent polarizations and different frequencies;
• bringing the thus-formed first interfering light beam out of said light path interval;
• forming a second interfering light beam as follows:
• separating a part of the light from the first interfering light beam;
• passing the part of separated light at least once along said preset light path interval;
• converting the polarization of said first colinear light component in the beam of separated light into the polarization of said second colinear light component while converting the polarization of said second colinear light component into the polarization of said first colinear light component;
• suppressing the component comprising the first of said polarizations suppressing in the beam of separated light;
• bringing the thus-formed second interfering beam of separated light out of said light path interval;
• mixing together said first and second interfering light beams brought out of said light path interval;
• separating a part of the light having the second of said polarizations;
• recording an interference pattern formed in the beam of separated light as follows:
• converting the interfered light having the second of said independent polarizations into an electric signal;
• measuring the phase of said electric signal;
• determining the desired optical length of said preset light path interval from the measured phase of said electric signal.

A method of measuring the distribution of a light path optical length within a preset interval across interfering light beams, said method comprising the following consecutive steps:

• building an original light beam in the following way:
• creating a beam of coherent light;
• separating two colinear components from said beam including a first light component and a second light component, having two independent polarizations, respectively;
• offsetting the light frequency of one of said components from the other of said components;
• presetting a light path interval;
• forming a number of interfering light beams from said original coherent light beam in such a manner that each next interfering light beams is formed from a preceding interfering light beam in the following way:
• separating part of the light beam from the preceding interfering light beam;
• passing the separated part of the light beam at least once along said preset light path interval;
• converting the polarization of said first light component in the beam of a separated light into the polarization of said second light component, and converting the polarization of said second light component into the polarization of said first light component;
• bringing each of said next interfering light beams out of said light path interval;
• mixing together said formed interfering light beams into a single beam of mixed light;
• dividing said beam of interfered light into two beams having said independent polarizations;
• recording an interference pattern in each of said divided beams of interfered light and performing the following operations at no less than two points on the cross-section of the interfering light beams:
• converting the interfered light having the first of said independent polarizations into an electric signal at the first of said points;
• converting the interfered light having the second of said independent polarizations into an electric signal at the first of said points;
• measuring the phases of the electric signals obtained at the first of said points;
• converting the interfered light having the first of said independent polarizations into an electric signal at no less than one other point;
• converting the interfered light having the second of said independent polarizations into an electric signal at no less than one other point;
• measuring the phases of the electric signals obtained at no less than one other point;
• obtaining the distribution of the light path optical length within a preset interval across the interfering light by the results of measurement of the phase of the electric signals obtained at said first and said other points.

A method of measuring the optical length of a preset light path interval, said method comprising the following consecutive steps:

• building up an original light beam in the following way:
• creating a beam of coherent light, having a first known wavelength;
• separating two colinear components from said beam including a first light component and a second light component, having two independent polarizations;
• offsetting the light frequency of one of said components with respect to the other light component;
• presetting a light path interval;
• forming a number of interfering light beams from said original coherent light beam in such a manner that each next interfering light beam is formed from a preceding interfering light beam in the following way:
• separating a part of the light from the preceding interfering light beam;
• passing the separated part of light along said preset light path interval;
• converting the polarization of said first light component into the polarization of said second light component, and converting the polarization of said second light component into the polarization of said first light component;
• bringing each of said next interfering light beams out of said light path interval;
• mixing together said formed interfering light beams into a single beam of interfered light;
• dividing said beam of interfered light into two beams having said independent polarizations;
• recording an interference pattern formed in each of the divided light beams having a first known wavelength as follows:
• converting the interfered light having the first of said independent polarizations into a first electric signal;
• converting the interfered light having the second of said independent polarizations into a second electric signal;
• measuring the phases of said electric signals;
• changing the wavelength of coherent light at least once by a known value;
• recording an interference pattern formed with each of the further known wavelengths, and measuring the phases of said first electric signal said second electric signal;
• determining an integral part of the wavelengths within a preset light path interval from the relation between the phases of the electric signals measured at different known wavelengths of coherent light;
• determining the optical length of a preset light path interval from the determined integral part of the wavelengths and from the measured phases of electric signals at the wavelength.

A digital multiple-beam laser interferometer, comprising:

• a laser capable of emitting a beam of coherent light;
• a device for separating from said light beam two collinear light components having mutually independent polarizations, said device being positioned past said laser along the run of the light beam;
• a device for offsetting the frequency of one of said light components, said device being positioned past said laser as along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• at least two reflecting elements placed one after the other as along the run of the original light beam and adapted for presetting a light path interval and forming the interfering light beams by virtue of multiple reflection of the light beam from said reflecting elements;
• a birefringent plate situated between said reflecting elements and adapted for mutual conversion of the polarizations of said light components;
• a polarizing element arranged on the axis of said formed interfering light beams past said reflecting elements and adapted for splitting the light of said interfering beams into two interfered light beams having said mutually independent polarizations;
• at least one photodetector located past said polarizing element on the axis of at least one of said interfered light beams and adapted for photoelectric conversion of the interfered light into an electric signal;
• at least one phase measuring unit connected to the output of at least one said photodetector and adapted for measuring the phase of at least one said electric signal, from which phase the optical length of a preset light path interval is judged.

A digital multiple-beam laser interferometer, comprising:

• a laser capable of emitting a beam of coherent light;
• a device for separating from said light beam two collinear light components having mutually independent polarizations, said device being situated past said laser as along the run of the light beam;
• a device for offsetting the frequency of one of said light components, said device being positioned past said laser along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• at least two reflecting elements placed one after the other along the run of the light beam and adapted for presetting a light path interval and forming a number of interfering light beams by virtue of multiple reflection of the light beam from said reflecting elements;
• a birefringent plate situated between said reflecting elements and adapted for mutual conversion of said polarizations of said light components;
• a beam-splitter element positioned between said light frequency offsetting device and said reflecting elements and adapted for separating said interfering beams reflected from said reflecting elements;
• a polarizing element situated past said beam-splitter element along the run of said separated interfering beams and adapted for splitting the light of said separated interfering beams into two interfered light beams having said mutually independent polarizations;
• at least one photodetector located past said polarizing element on the axis of at least one of said interfered light beams and adapted for photoelectric conversion of the interfered light into an electric signal;
• at least one phase measuring unit connected to the output of at least one said photodetector and adapted for measuring the phase of at least one said electric signal so as to judge of the desired optical length of a preset light path interval by said phase.

A digital multiple-beam laser interferometer, comprising:

• a laser capable of emitting a beam of coherent light;
• a device for separating from said light beam two collinear light components having mutually independent polarizations, said device being situated past said laser along the run of the light beam;
• a device for offsetting the light frequency of one of said light components, said device being situated past said laser along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• at least three reflecting elements positioned one after another as along the run of the light beam at the corners of a closed polygon and adapted for presetting a closed light path interval and for forming a number of interfering light beams by virtue of multiple reflection of the light beam from said reflecting elements;
• a birefringent plate placed between said reflecting elements and adapted for mutual conversion of said polarizations of said light components;
• a polarizing element placed on the axis of said formed interfering beams past said reflecting elements and adapted for dividing the light of said interfering beams into two interfered light beams having said mutually independent polarizations;
• at least one photodetector situated past said polarizing element on the axis of at least one of said two interfered light beams and adapted for photoelectric conversion of the interfered light into an electric signal;
• at least one phase measuring unit connected to the output of at least one said photodetector and adapted for measuring the phase of at least one said electric signal so as to judge of the desired optical length of a preset light path interval by said phase.

A digital multiple-beam laser interferometer, comprising:

• a laser capable of emitting a beam of coherent light;
• a device for separating from said light beam two collinear light components having mutually independent polarizations, said device being situated past said laser as along the run of the light beam;
• a device for offsetting the light frequency of one of said light components, said device being situated past said laser along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• an optical system adapted for expanding an original light beam and located past the light frequency offsetting device;
• at least two reflecting elements placed one after the other along the run of the light beam and adapted for presetting a light path interval and for forming a number of interfering beams by virtue of multiple reflection of the light beam from said reflecting elements;
• a birefringent plate placed between said reflecting elements and adapted for mutual conversion of said polarizations of said light components;
• a polarizing element positioned on the axis of said formed interfering beams past said reflecting elements and adapted for dividing the light of said interfering beams into two interfered light beams having said mutually independent polarizations;
• at leeast one photoelectric converter of interfered light into an electric signal, located past said polarizing element on the axis of at least one of said two interfered light beams;
• at least one phase measuring unit connected to the output of at least one of said photoelectric converters and adapted for measuring the phase of at least one said electric signal so as to judge of the desired optical length of a light path interval by said phase.

A digital multiple-beam laser interferometer adapted for measuring the distribution of the light path optical length, comprising:

• a laser capable of emitting a beam of coherent light;
• a device for separating from said light beam two collinear light components having mutually independent polarizations, said device being located past said laser along the run of the light beam;
• a device for offsetting the light frequency of one of said light components, said device being located past said laser along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• a device for displacing the original light beam parallel to itself in two mutually square directions, said device being located past the light frequency offsetting device along the run of the light beam;
• a least two reflecting elements positioned one after the other as along the run of the light beam and adapted for presetting a light path interval and for forming a number of intefering light beams by virtue of multiple reflection of said light beam;
• a birefringent plate positioned between said reflecting elements and adapted for mutual conversion of said mutually independent polarizations of said light components;
• a polarizing elements arranged on the axis of said formed interfering beams past said reflecting elements and adapted for dividing the light of said interfering light beams into two interfered light beams with said mutually independent polarizations;
• at least one photoelectric converter of interfered light into an electric signal, said converter being located past said polarizing element on the axis of at least one of said two beams of interfered light;
• at least one phase measuring unit connected to the output of at least one of said photoelectric converters and adapted for measuring the phase of at least one said electric signal so as to judge of the distribution on the desired light path optical length by said phase.

A digital multiple-beam laser interferometer, comprising:

• a laser capable of emitting a beam of coherent light;
• a device for separating from said light beam two collinear light components with mutually independent polarizations, said device being located past said laser along the run of the light beam;
• a device for offsetting the light frequency of one of said light components, said device being located past said laser along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• an optical system adapted for expanding the original light beam and located past the light frequency offsetting device;
• at least two reflecting elements positioned one after the other along the run of the light beam and adapted for presetting a light path interval and for forming a number of interfering light beams by virtue of multiple reflection of said light beam;
• a birefringent plate located between said reflecting elements and adapted for mutual conversion of said independent polarizations of said light components;
• an optical element arranged on the axis of said formed interfering beams past said reflecting elements and adapted for separating part of the light of the interfering beams;
• a first polarizing element arranged on the axis of said interfering light beams past said optical element and adapted for splitting the light of said interfering light beams into two beams, a first and a second, of interfered light with said mutually independent polarizations;
• a second polarizing element arranged on the axis of the beam of said separated part of the light of the interfering light beams past said optical element and adapted for dividing the light of said beam of separated part of light into two beams, a third and a fourth, of interfered light with said mutually independent polarizations;
• at least one main photoelectric converter of interfered light into an electric signal, said main photoelectric converter being located past said first polarizing element at no less than one preset point across at least one of said two, the first and the second, beams of interfered light;
• at least one additional photoelectric converter of interfered light into an electric signal, said additional photoelectric converter being located past said second polarizing element at no less than one reference point across at least one of said two, the third and the fourth, beams of interfered light;
• at least one main phase measuring unit connected to the output of at least one said main photoelectric converter and adapted for measuring the phase of at least one said electric signal so as to judge of the optical length of a preset light path interval at no less than one said preset point across said light beam by said measured phase;
• at least one additional phase measuring unit connected to the output of at least one said additional photoelectric converter and adapted for measuring the phase of at least one said electric signal so as to judge of the optical length of a preset light path interval by said measured phase, at no less than one said preset reference points across said light beam.

a digital multiple-beam laser interferometer, comprisng:

• a laser capable of emitting a beam of coherent light;
• a device for separating from said light beam two collinear light components with mutually independent polarizations, said device being located past said laser along the run of the light beam;
• a device for offsetting the light frequency of one of said light components, said device being located past said laser along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• at least two reflecting elements positioned one after the other along the run of the light beam and adapted for presetting a light path interval and for forming a number of interfering light beams by virtue of multiple reflection of said light beam from said reflecting elements;
• a birefringent plate located between said reflecting elements and adapted for mutual conversion of said independent polarizations of said light components;
• at least one device for changing the optical length of light path within a preset interval, said device being located between said reflecting elements and adapted for controlled variation of the light path optical length along at least one ray in a light beam;
• at least one transducer for sensing a change in the light path optical length, said transducer being connected to said device for changing the light path optical length;
• a polarizing element arranged on the axis of said formed interfering beams past said reflecting elements along the run of the light beam and adapted for dividing the light of said interfering beams into two beams of interfered light with said mutually independent polarizations;
• at least one photodetector located past said polarizing element on the axis of at least one of said two beams of interfered light and adapted for photoelectric conversion of the interfered light into an electric signal;
• at least one phase measuring unit connected to the output of at least one of said photodetectors and adapted for measuring the phase of at least one said electric signal;
• at least one phase value presetting unit adapted for presetting phase values corresponding to the known values of the light path optical length;
• at least one phase comparator unit whose inputs are connected to at least one said phase measuring unit and to at least one said phase value presetting unit, while the output of said phase comparator unit is connected to at least one said device for changing the light path optical length, said phase comparator unit being adapted for comparing the measured phase value with a preset value thereof, generating an error signal dependent upon the results of phase comparison and controlling, by means of said error signal, a change in the light path optical length along at least one ray of a light beam;
• a computer device connected to the outputs of at least one said phase measuring unit and of at least one said transducer for sensing a change in the light path optical length, said computer device being adapted for determining the desired optical length of a preset light path interval from the results of measurement of the phases of electric signals and from the value of a change in the light path optical length.

A digital multiple-beam laser interferometer capable of simultaneous visual observation of an interference pattern, said interferometer comprising:

• a laser capable of emitting a beam of coherent light;
• a device for separating from said light beam two collinear light components with mutually independent polarizations, said device being located past said laser along the run of the light beam;
• a device for offsetting the light frequency of one of said light components, said device being located past said laser along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• an optical system for expanding the light beam, said system being located past the light frequency offsetting device;
• at least two reflecting elements arranged one after the other as along the run of the light beam and adapted for presetting a light path interval and for forming a number of interfering light beams by virtue of multiple reflection of the light beam from said reflecting elements;
• a birefringent plate located between said reflecting elements and adapted for mutual conversion of said polarizations of said light components;
• a beam-splitter element located between said light frequency offsetting device on the one side and said reflecting elements on the other side and adapted for separating the interfering light beams reflected from said reflecting elements;
• a polarizing element located past said beam-splitter element along the run of said reflected interfering light beams;
• at least one photoelectric converter of the interfered light into an electric signal, said converter being located past said polarizing element on the axis of at least one of said two beams of interfered light;
• at least one phase measuring unit connected to the output of at least one said photoelectric converter and adapted for measuring the phase of at least one said electric signal so as to judge of the desired optical length of a preset light path interval by said phase;
• an optical beam-splitter element located on the axis of the interfering light beams between said reflecting elements on the one side and at least one said photoelectric converter on the other side and adapted for separating part of the light of the interfering beams for visual observation of the interference pattern;
• a light intensity modulator located past said optical beam-splitter element on the axis of the beam of the separated part of light of the interfering light beams and adapted for the separated part of light of the interfering light beams to pass at preset short time intervals;
• an interference pattern image recorder located past said light intensity modulator along the run of the beam of the separated part of light of the interfering beams and adapted for recording or visually observing the resulting interference pattern;
• a pulse generator connected to said light intensity modulator and adapted for controlling said modulator by setting electric pulses within said short time intervals.

A digital multiple-beam laser interferometer, comprising:

• a laser capable of emitting a beam of coherent light having different wavelengths;
• a device for separating from said light beam two collinear light components with mutually independent polarizations, said device being located past said laser along the run of the light beam;
• a device for offsetting the light frequency of one of said light components, said device being located past said laser along the run of the light beam;
• a master oscillator connected to said light frequency offsetting device;
• at least two reflecting elements positioned one after the other along the run of the light beam and adapted for presetting a light path interval and for forming a plurality of interfering light beams by virtue of multiple reflection of the light beam from said reflecting elements;
• a birefringent plate located between said reflecting elements and adapted for mutual conversion of said polarizations of said light components;
• a beam-splitter element located between said light frequency offsetting device on the one side and said reflecting elements on the other side and adapted for separating said interfering light beams reflected from said reflecting elements;
• a polarizing element located past said beam-splitter element along the run of said separated interfering light beams and adapted for dividing the light of said interfering beams into two beams of interfered light with said independent polarizations;
• at least one photoelectric converter of the interfered light into an electric signal, said converter being located past said polarizing element on the axis of at least one of said two beams of interfered light;
• at least one phase measuring unit connected to the output of at least one said photoelectric converter and adapted for measuring the phase of said electric signal so as to judge of the desired optical length of a preset light path interval by said phase;
• a computer device connected to the output of at least one said phase measuring unit and to said laser and adapted for calculating an integral and a fraction part of the periods of the desired value of the optical length of a preset light path interval from the results of measuring the phases of electric signals at different known values of said laser wavelengths.