Editing Michelson interferometer (section)

===Phase-conjugating interferometry ===
The reflection from phase-conjugating mirror of two light beams inverses their phase difference 
<math>\Delta \varphi</math> to the opposite one <math>-\Delta \varphi</math>. For this reason the interference pattern in twin-beam interferometer changes drastically. Compared to conventional Michelson interference curve with period of half-wavelength <math>\lambda/2</math>:
<math display="block">I(\Delta L) \sim [1+ \gamma(\Delta L) \cos (2k\Delta L)],</math>
where <math>\gamma(\Delta L)</math> is second-order correlation function, the interference curve in phase-conjugating  interferometer <ref name="Okulov, A YU 1980">{{cite journal |title=Laser interferometer with wavefront reversing mirrors
|journal=Sov. Phys. JETP|volume=52 |issue=5 |pages=847 |year=1980 
|last1= Basov |first1=N G
|last2= Zubarev |first2=I G
|last3= Mironov |first3=A B
|last4= Michailov |first4= S I
|last5= Okulov |first5= A Yu
|bibcode=1980ZhETF..79.1678B}}</ref>
has much longer period defined by frequency shift <math>\delta \omega = \Delta k c</math> of reflected beams:
<math display="block">I(\Delta L) \sim [1+ [\gamma(\Delta L)+0.25] \cos (\Delta k\Delta L)],</math>
where visibility curve is nonzero when optical path difference <math>\Delta L > \ell_\text{coh}</math> exceeds coherence length of light beams. 
The nontrivial features of phase fluctuations in optical phase-conjugating mirror had been studied via  Michelson interferometer with two independent PC-mirrors 
.<ref name="Okulov, A YU 1980J">{{cite journal |title=Phase fluctuations of the Stockes wave produced as a result of stimulated scattering of light
|journal=Sov. Phys. JETP Lett.|volume=31 |issue=11 |pages=645 |year=1980 
|last1= Basov |first1=N G
|last2= Zubarev |first2=I G
|last3= Mironov |first3=A B
|last4= Michailov |first4= S I
|last5= Okulov |first5= A Yu
|bibcode=1980JETPL..31..645B}}</ref> The phase-conjugating Michelson interferometry is a promising technology  for coherent summation of laser amplifiers.<ref name="Boyd, R W 1997">{{cite journal |title=Brillouin-enhanced four-wave-mixing vector phase-conjugate mirror with beam-combining capability
|journal=Optics Letters|volume=22 |issue=6 |pages=360–362  |year=1997 
|last1= Bowers |first1=M W
|last2= Boyd |first2=R W
|last3= Hankla |first3=A K
|doi=10.1364/OL.22.000360|pmid=18183201|bibcode=1997OptL...22..360B|s2cid=25530526 }}</ref>
Constructive interference in an array containing  <math>N/2</math> beamsplitters of <math>N</math> laser beams synchronized by 
[[phase conjugation]]
may increase the brightness of amplified beams as <math>N^2</math>.<ref name="Okulov, A Yu 2014">{{cite journal | title=Coherent chirped pulse laser network with Mickelson phase conjugator | journal=Applied Optics | volume=53 | issue=11 | pages=2302–2311 | year=2014 | last1= Okulov |first1=A Yu|doi=10.1364/AO.53.002302 | pmid = 24787398 | arxiv = 1311.6703 | bibcode=2014ApOpt..53.2302O | s2cid = 118343729 }}</ref>