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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Optical parametric amplifier</span></span>

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<p>An <b>optical parametric amplifier</b>, abbreviated <b>OPA</b>, is a <a href="Laser" title="Laser">laser</a> light source that emits light of variable <a href="Wavelength" title="Wavelength">wavelengths</a> by an optical <a href="Parametric_amplifier" class="mw-redirect" title="Parametric amplifier">parametric amplification</a> process. It is essentially the same as an <a href="Optical_parametric_oscillator" title="Optical parametric oscillator">optical parametric oscillator</a>, but without the <a href="Optical_cavity" title="Optical cavity">optical cavity</a> (i.e., the light beams pass through the apparatus just once or twice, rather than many many times).

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<div class="mw-heading mw-heading2"><h2 id="Optical_parametric_generation_(OPG)">Optical parametric generation (OPG)</h2></div>

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</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Spontaneous_parametric_down_conversion" class="mw-redirect" title="Spontaneous parametric down conversion">Spontaneous parametric down conversion</a></div>

<p>Optical parametric generation (OPG) (also called "optical parametric fluorescence", or "<a href="Spontaneous_parametric_down_conversion" class="mw-redirect" title="Spontaneous parametric down conversion">spontaneous parametric down conversion</a>") often precedes optical parametric amplification.

</p><p>In <a href="Optical_parametric_generation" class="mw-redirect" title="Optical parametric generation">optical parametric generation</a>, the input is one light beam of frequency ω<sub>p</sub>, and the output is two light beams of lower frequencies ω<sub>s</sub> and ω<sub>i</sub>, with the requirement ω<sub>p</sub>=ω<sub>s</sub>+ω<sub>i</sub>. These two lower-frequency beams are called the "signal" and "idler", respectively.

</p><p>This <a href="Light_emission" class="mw-redirect" title="Light emission">light emission</a> is based on the <a href="Nonlinear_optics" title="Nonlinear optics">nonlinear optical principle</a>. The <a href="Photon" title="Photon">photon</a> of an incident laser pulse (pump) is, by a nonlinear optical crystal, divided into two lower-energy photons. The wavelengths of the signal and the idler are determined by the phase matching condition, which is changed, e.g. by temperature or, in bulk optics, by the angle between the incident pump laser ray and the optical axes of the crystal. The wavelengths of the signal and the idler photons can, therefore, be tuned by changing the <a href="Phase_matching" class="mw-redirect" title="Phase matching">phase matching</a> condition.

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<div class="mw-heading mw-heading2"><h2 id="Optical_parametric_amplification_(OPA)">Optical parametric amplification (OPA)</h2></div>

<p>The output beams in optical parametric generation are usually relatively weak and have relatively spread-out direction and frequency. This problem is solved by using optical parametric amplification (OPA), also called <a href="Nonlinear_optics" title="Nonlinear optics">difference frequency generation</a>, as a second stage after the OPG.

</p><p>In an OPA, the input is <i>two</i> light beams, of frequency ω<sub>p</sub> and ω<sub>s</sub>. The OPA will make the pump beam (ω<sub>p</sub>) weaker, and <i>amplify</i> the signal beam (ω<sub>s</sub>), and also create a new, so-called idler beam at the frequency ω<sub>i</sub> with ω<sub>p</sub>=ω<sub>s</sub>+ω<sub>i</sub>.

</p><p>In the OPA, the pump and idler photons usually travel collinearly through a nonlinear optical crystal. <a href="Phase_matching" class="mw-redirect" title="Phase matching">Phase matching</a> is required for the process to work well.

</p><p>Because the wavelengths of an OPG+OPA system can be varied (unlike most lasers which have a fixed wavelength), they are used in many <a href="Spectroscopy" title="Spectroscopy">spectroscopic methods</a>.

</p><p>As an example of OPA, the incident pump pulse is the 800 nm (12500 cm<sup>−1</sup>) output of a <a href="Ti-sapphire_laser" class="mw-redirect" title="Ti-sapphire laser">Ti:sapphire laser</a>, and the two outputs, signal and idler, are in the near-infrared region, the sum of the <a href="Wavenumber" title="Wavenumber">wavenumber</a> of which is equal to 12500 cm<sup>−1</sup>.

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<div class="mw-heading mw-heading2"><h2 id="Noncollinear_OPA_(NOPA)">Noncollinear OPA (NOPA)</h2></div>

<p>Because most nonlinear crystals are <a href="Birefringent" class="mw-redirect" title="Birefringent">birefringent</a>, beams that are collinear inside a crystal may not be collinear outside of it. The phase fronts (<a href="Wave_vector" title="Wave vector">wave vector</a>) do not point in the same direction as the energy flow (<a href="Poynting_vector" title="Poynting vector">Poynting vector</a>) because of walk-off.

</p><p>The <a href="Nonlinear_optics#Phase_matching" title="Nonlinear optics">phase matching angle</a> makes possible any gain at all (0th order). In a collinear setup, the freedom to choose the center wavelength allows a constant gain up to first order in wavelength. Noncollinear OPAs were developed to have an additional degree of freedom, allowing constant gain up to second order in wavelength. The optimal parameters are 4 degrees of noncollinearity, <a href="%CE%92-barium_borate" class="mw-redirect" title="Β-barium borate">β-barium borate</a> (BBO) as the material, a 400-nm pump wavelength, and signal around 800 nm (and can be tunable in the range 605-750 nm with sub-10 fs pulse width which allows exploring the ultrafast dynamics of large molecules<sup id="cite_ref-Jarota_2019_192–204_1-0" class="reference"><a href="#cite_note-Jarota_2019_192–204-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>) This generates a bandwidth 3 times as large of that of a <a href="Ti-sapphire_laser" class="mw-redirect" title="Ti-sapphire laser">Ti-sapphire</a>-amplifier. The first order is mathematically equivalent to some properties of the group velocities involved, but this does not mean that pump and signal have the same group velocity. After propagation through 1-mm BBO, a short pump pulse no longer overlaps with the signal. Therefore, <a href="Chirped_pulse_amplification" title="Chirped pulse amplification">chirped pulse amplification</a> must be used in situations requiring large gain amplification in long crystals. Long crystals introduce such a large <a href="Chirp" title="Chirp">chirp</a> that a compressor is needed anyway. An extreme chirp can lengthen a 20-fs seed pulse to 50 ps, making it suitable for use as the pump.<sup id="cite_ref-Jarota_2019_192–204_1-1" class="reference"><a href="#cite_note-Jarota_2019_192–204-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> Unchirped 50-ps pulses with high energy can be generated from rare earth-based lasers.

</p><p>The optical parametric amplifier has a wider bandwidth than a -amplifier, which in turn has a wider bandwidth than an optical parametric oscillator because of white-light generation even one octave wide (for example using nonlinear <a href="Self-phase_modulation" title="Self-phase modulation">self-phase modulation</a> in neon gas<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>). Therefore, a subband can be selected and fairly short pulses can still be generated.

</p><p>The higher gain per mm for BBO compared to Ti:Sa and, more importantly, lower <a href="Amplified_spontaneous_emission" title="Amplified spontaneous emission">amplified spontaneous emission</a> allows for higher overall gain.

Interlacing compressors and OPA leads to tilted pulses.

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<div class="mw-heading mw-heading2"><h2 id="Multipass_OPA">Multipass OPA</h2></div>

<p>Multipass can be used for

walk off and <a href="Group_velocity" title="Group velocity">group velocity</a> (<a href="Dispersion_(optics)" title="Dispersion (optics)">dispersion</a>) compensation;

constant intensity with increasing signal power means to have an exponential rising cross section. This can be done by means of lenses, which also refocus the beams to have the beam waist in the crystal;

reduction of OPG by increasing the pump power proportional to the signal and splitting the pump across the passes of the signal;

broadband amplification by dumping the idler and optionally individually detuning the crystals;

complete pump depletion by offsetting the pump and signal in time and space at every pass and feeding one pump pulse through all passes;

high gain with BBO, since BBO is only available in small dimensions.

Since the direction of the beams is fixed, multiple passes cannot be overlapped into a single small crystal like in a Ti:Sa amplifier. Unless one uses noncolinear geometry and adjusts amplified beams onto the parametric fluorescence cone produced by the pump pulse.<sup id="cite_ref-Jarota_2019_192–204_1-2" class="reference"><a href="#cite_note-Jarota_2019_192–204-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="Relationship_to_parametric_amplifiers_in_electronics">Relationship to parametric amplifiers in electronics</h2></div>

<div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Parametric_amplifier" class="mw-redirect" title="Parametric amplifier">Parametric amplifier</a></div>

<p>The idea of parametric amplification first arose at much lower frequencies: AC circuits, including radio frequency and microwave frequency (in the earliest investigations, sound waves were also studied). In these applications, typically a strong pump signal (or "<a href="Local_oscillator" title="Local oscillator">local oscillator</a>") at frequency <i>f</i> passes through a circuit element whose parameters are modulated by the weak "signal" wave at frequency <i>f</i><sub>s</sub> (for example, the signal might modulate the capacitance of a <a href="Varactor_diode" class="mw-redirect" title="Varactor diode">varactor diode</a><sup id="cite_ref-Das_4-0" class="reference"><a href="#cite_note-Das-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>). The result is that some of the energy of the local oscillator gets transferred to the signal frequency <i>f</i><sub>s</sub>, as well as the difference ("idler") frequency <i>f</i>-<i>f</i><sub>s</sub>. The term <i>parametric</i> amplifier is used because the <i>parameters</i> of the circuit are varied.<sup id="cite_ref-Das_4-1" class="reference"><a href="#cite_note-Das-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>

</p><p>The optical case uses the same basic principle—transferring energy from a wave at the pump frequency to waves at the signal and idler frequencies—so it took the same name.

</p>

<ul><li><a href="Optical_parametric_oscillator" title="Optical parametric oscillator">Optical parametric oscillator</a></li>

<li><a href="SU(1%2C1)_interferometry" title="SU(1,1) interferometry">SU(1,1) interferometry</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Footnotes_and_references">Footnotes and references</h2></div>

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</style><cite id="CITEREFJarotaPastorczakTawfikXue2019" class="citation journal cs1">Jarota, Arkadiusz; Pastorczak, Ewa; Tawfik, Walid; Xue, Bing; Kania, Rafał; <a href="Halina_Abramczyk" title="Halina Abramczyk">Abramczyk, Halina</a>; Kobayashi, Takayoshi (2019). <span class="id-lock-subscription" title="Paid subscription required"><a rel="nofollow" class="external text" href="http://xlink.rsc.org/?DOI=C8CP05882B">"Exploring the ultrafast dynamics of a diarylethene derivative using sub-10 fs laser pulses"</a></span>. <i>Physical Chemistry Chemical Physics</i>. <b>21</b> (1): <span class="nowrap">192–</span>204. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2019PCCP...21..192J">2019PCCP...21..192J</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1039%2FC8CP05882B">10.1039/C8CP05882B</a>. <a href="ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/1463-9076">1463-9076</a>. <a href="PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/30516769">30516769</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:54561976">54561976</a>.</cite></span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><cite id="CITEREFTawfik2016" class="citation journal cs1">Tawfik, Walid (August 2016). <span class="id-lock-subscription" title="Paid subscription required"><a rel="nofollow" class="external text" href="https://linkinghub.elsevier.com/retrieve/pii/S0969806X16301165">"Reaching white-light radiation source of ultrafast laser pulses with tunable peak power using nonlinear self-phase modulation in neon gas"</a></span>. <i>Radiation Physics and Chemistry</i>. <b>125</b>: <span class="nowrap">165–</span>170. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2016RaPC..125..165T">2016RaPC..125..165T</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1016%2Fj.radphyschem.2016.04.006">10.1016/j.radphyschem.2016.04.006</a>.</cite></span>

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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external free" href="http://link.aip.org/link/?APPLAB/86/211120/1">http://link.aip.org/link/?APPLAB/86/211120/1</a> Multipass bow type chirped pulse amplifier</span>

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<li id="cite_note-Das-4"><span class="mw-cite-backlink">^ <a href="#cite_ref-Das_4-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Das_4-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><cite id="CITEREFDasDas2019" class="citation book cs1">Das, Annapurna; Das, Sisir K. (18 February 2019). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=ZU19Uemy83YC&pg=PA397"><i>Microwave Engineering</i></a>. Tata McGraw-Hill Education. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>9780074635773</bdi> – via Google Books.</cite></span>

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<ul><li>Boichenko, V.L.; Zasavitskii, I.I.; Kosichkin, Yu.V.; Tarasevich, A.P.; Tunkin, V.G.; Shotov, A.P. (1984) "A picosecond optical parametric oscillator with amplification of the tunable semiconductor laser radiation", <a href="Soviet_Journal_of_Quantum_Electronics" class="mw-redirect" title="Soviet Journal of Quantum Electronics">Soviet Journal of Quantum Electronics</a> 11 (1): 141–143.</li>

<li>Magnitskii, S.A.; Malakhova, V.I.; Tarasevich, A.P.; Tunkin, V.G.; Yakubovich, S.D. (1986) "Generation of bandwidth-limited tunable picosecond pulses by injection-locked optical parametric oscillator", <a href="Optics_Letters" title="Optics Letters">Optics Letters</a> 11 (1): 18–20.</li></ul>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="https://www.sas.rochester.edu/chm/groups/mccamant/assets/pdf/documents_nopa.pdf">Guide to NOPAs</a></li>

<li><a rel="nofollow" class="external text" href="http://www.bmo.physik.uni-muenchen.de/~wwwriedle/projects/NOPA_overview/NOPA_overview.php">NOPA and Group Velocity</a></li>

<li><a rel="nofollow" class="external text" href="http://www.bmo.physik.uni-muenchen.de/forschung/zinth/massschneidern/">Rainbow in photo</a></li></ul></div><div><div class="zim-footer">

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