knight_1990 =========== P\. L\. Knight, M\. A\. Lauder and B\. J\. Dalton, "Laser\-induced continuum structure", Phys\. Rep\. 190, 1 \(1990\) `Source record `__ · :doc:`Catalogue ` · :doc:`Review register ` DOI: `10\.1016/0370\-1573\(90\)90089\-K `__ **Source kind:** theory **Recorded technique:** Review of laser\-induced continuum structure \(LICS\)\: a bound state coupled to a flat continuum in the Markov approximation \(Sec\. 2\.2\), Fano states \(Sec\. 2\.3\), two bound states strongly coupled to a common continuum by two lasers, with ionisation widths, continuum light shifts and a complex two\-photon coupling \(Sec\. 2\.4\), laser phase fluctuations in the phase\-diffusion model, extra ionisation channels and Raman coupling through discrete states in a quantised\-field master equation \(Sec\. 3\), pulse shapes \(Sec\. 4\), and the experiments in Cs, Na and Xe \(Sec\. 5\)\. Model parameters \(ionisation rates in Mrad/s, Fano q\) only\. **Materials in structured entries:** None recorded. **Dataset quantities:** None recorded. **Contents:** 0 datasets; 0 formulas. Curation notes -------------- Nothing extracted\: a review of model calculations; the only noble\-gas content is Hutchinson and Ness's xenon experiment, reported as a figure of signal against embedding\-laser frequency at 80 MW/cm^2 \(embedding\) and 30 and 35 MW/cm^2 \(probe\) \(Fig\. 5\.4, p\. 57\), with no strengths, shifts or widths \(Rule 7\)\. Pages are the journal's \(1\-61\); PDF page = journal page \(p\. 1 is the title page\)\. Identity checked against p\. 2\: 'PHYSICS REPORTS \(Review Section of Physics Letters\) 190, No\. 1 \(1990\) 1\-61', received October 1989\. The library copy is a scan; Eqs\. 2\.8\-2\.12 were read from the page images \(pp\. 12\-13\)\. WHAT BEARS ON OEP 8 \(sections 4\.3\-4\.5\)\: \(1\) Ionisation width \(Sec\. 2\.2, pp\. 10\-13\)\. For V = V^0\(t\) cos\(omega\_L t \+ Phi\) and an energy\-normalised continuum, Omega\_0eps = \<0\|V^0\|C,eps\>/hbar; in the RWA and Markov approximation the bound amplitude obeys Eq\. 2\.9, with the level shift delta E = \-hbar P integral d eps \|Omega\_0eps\|^2/\(4 Delta\_eps\) \(Eq\. 2\.10, Delta\_eps = omega\_eps \- omega\_0 \- omega\_L\) and the population P\_0 = exp\(\-integral Gamma dt\), Gamma\(t\) = \(1/2\) pi hbar \|Omega\_0eps\_i\(t\)\|^2 \(Eqs\. 2\.11\-2\.12; 'note V = Omega hbar/2 in the RWA'\)\. Gamma is a population rate following the instantaneous intensity\. With Phi = I/\(hbar omega\) and I = \(1/2\) eps\_0 c E\_0^2 this is Gamma = sigma Phi with sigma = pi omega \|mu\|^2/\(eps\_0 c\), 4 pi^2 alpha omega \|mu\|^2 in a\.u\. \(derived 2026\-10\-09\)\: OEP 8's Gamma^PI\_f = sigma^PI\_f Phi, and the imaginary energy \-i hbar Gamma/2 equals \-i Im alpha\_f \|E^\+\|^2 with Im alpha\_f = eps\_0 c sigma/omega, OEP 8's relation in section 4\.3\. \(2\) The two\-level equations with two lasers \(Sec\. 2\.4, pp\. 18\-22\)\. Eq\. 2\.63\: diagonal delta E\_j/hbar \- \(i/2\) Gamma\_j \(\+ the Raman detuning D^ab on level 1\), off\-diagonal \-\(1/2\) Gamma \(q \+ i\), with Gamma\_j \(Eq\. 2\.59\) and delta E\_j \(Eq\. 2\.60\) the sums over both lasers of the forms \(1\), Gamma = \(1/2\) pi hbar Omega^a\_0eps' Omega^b\_eps'1 ~ sqrt\(Gamma\_0^a Gamma\_1^b\) \(Eq\. 2\.61\), delta E the principal\-value two\-photon coupling through the continuum \(Eq\. 2\.62\) and q = delta E/\(\(1/2\) hbar Gamma\) \(Eq\. 2\.65\)\. The review excludes \(p\. 20\) the self\-couplings via the continuum and the far\-detuned Raman couplings, and \(p\. 40\) 'the possible direct two\-photon resonant transition \|0\> \+ 2 omega\_b \-\> \|1\>', which is OEP 8's case\: the review treats the Lambda \(Raman\) geometry through the continuum, not a two\-photon ladder from the ground state\. \(3\) Light shifts with both rotating terms \(Sec\. 3\.3, pp\. 37\-41\)\. With E\_0c cos\(omega\_c t\) and xi = \ E\_0c/hbar, the Stark shift of the transition \(Eq\. 3\.29\) sums \-\(1/4\) xi^2 \[1/\(omega\_v1 \+ omega\_c\) \+ 1/\(omega\_v1 \- omega\_c\)\] over virtual bound states and the corresponding principal\-value continuum integrals\: each level moves by \-alpha \|E^\+\|^2 with alpha the full dynamic polarisability \(derived 2026\-10\-09\), OEP 8's convention\. The text \(p\. 40\) notes that Eqs\. 2\.60 and 2\.62 'included only resonant terms'; the two\-photon Rabi frequency Omega^\(2\)\_01 \(Eq\. 3\.34\) is complex, its real part from discrete and principal\-value continuum terms, its imaginary part from the continuum, and q = Re Omega^\(2\)/Im Omega^\(2\) \(Eq\. 3\.35\)\. \(4\) Laser noise \(Sec\. 3\.2, pp\. 32\-34\)\. In the phase\-diffusion model \(Lorentzian spectra\) the averaged density\-matrix equations \(Eq\. 3\.10\) gain \-i Delta on the coherences, Delta = Delta\_aa \+ Delta\_bb \- 2 Delta\_ab \(Eq\. 3\.9\)\: laser phase noise acts as pure dephasing of the two\-photon coherence\. For a two\-photon ladder driven by one laser the phase is 2 Phi, giving 4 Delta\_aa \(derived 2026\-10\-09; not in the review\), a term OEP 8's gamma^phi would carry for a phase\-diffusing source\. \(5\) Pulse shape \(Sec\. 4\.2, pp\. 49\-52\)\. Gaussian pulses compared with flat ones of equal energy; the Stark shifts are omitted because in the xenon experiment 'these shifts are measured to be an order of magnitude less than the peak\-to\-window spacing' \(p\. 52\), with the warning that intensity\-dependent shifts 'cause the whole energy axis to move over the duration of the pulse' and must be validated\. kumar\_2026's Eqs\. 10\-11 \(refs\. 51\-52\: this review and toth\_2023\)\: its continuum shift delta E\_e = \-P integral dE \|mu\_eE\|^2 \|eps\_P\|^2/\(4 hbar \(omega\_E \- omega\_P \- omega\_e\)\) is Eq\. 2\.10 term for term \(Omega = mu eps\_P/hbar\), and its Gamma\_e = \(pi/\(2 hbar\)\) \|eps\_P\|^2 \|\\|^2 is Eq\. 2\.12\. So Kumar et al\.'s continuum shift is the resonant term only; the counter\-rotating continuum term, which Eq\. 3\.29 includes, is not in kumar\_2026's Eqs\. 8 and 10 as written \(Eq\. 8 sums over the bound p states with both terms\)\. Its size for He 1s2s is not known here\. No numbers of kumar\_2026 appear in this review \(no helium is treated\)\. FINDING \(OEP 8 section 4\.4, comment 2026\-10\-09\)\: Eqs\. 2\.59\-2\.63 show that two bound levels ionised into a common continuum acquire a complex off\-diagonal coupling of magnitude about sqrt\(Gamma\_0 Gamma\_1\) \(Eq\. 2\.61\)\. In OEP 8 the \(2\+1\) ionisation of f \(final energy E\_f \+ hbar omega\) and the direct three\-photon ionisation of g \(E\_g \+ 3 hbar omega\) reach the same continuum energy at two\-photon resonance, so the same kind of cross term exists; OEP 8 counts the two channels as additive\. FURTHER DATA CITED, not in the library\: M\. H\. R\. Hutchinson and K\. M\. M\. Ness, Phys\. Rev\. Lett\. 60, 105 \(1988\) and J\. Opt\. Soc\. Am\. B 1, 519 \(1984\) \(LICS in three\-photon ionisation of xenon\); X\. Tang, A\. L'Huillier and P\. Lambropoulos, Phys\. Rev\. Lett\. 62, 111 \(1989\), and M\. H\. R\. Hutchinson and K\. M\. M\. Ness, Phys\. Rev\. Lett\. 62, 112 \(1989\) \(the xenon line shapes and collisional dephasing\); B\. Dai and P\. Lambropoulos, Phys\. Rev\. A 36, 5205 \(1987\) and G\. Alber and P\. Zoller, Phys\. Rev\. A 27, 1713 \(1983\) \(q parameters of Na and Cs\)\. **Recorded bibliographic identity status:** VALIDATED\_WITH\_WARNINGS. This concerns identification of the source; it does not establish the scientific correctness of its contents. Datasets -------- No datasets are recorded. Formulas -------- No formulas are recorded. Corrections ----------- No dataset errata are recorded in this source record. Formula corrections, where recorded, appear with their formulas above. Curation notes may also discuss corrections or unresolved interpretation. Consult the :doc:`review register ` for the checks and decisions.