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Intrinsic picosecond stimulated emission and emission-excited picosecond optoelectronic nonlinear effects in GaAs

The above title is the subject of long-term studies carried out in Kotelnikov IRE RAS. Some of them are made in collaboration with V.I. Perel and other scientists from the A.F. Ioffe FTI RAS, SCLI VSU, and K.I. Satpayev KNRTU. The experiments were performed at room temperature. We studied the processes occurring in a thin (~ 1 µm) GaAs layer, pumped by a powerful picosecond light pulse. The discovered physical phenomena are listed in Sections I-IV. In Section V, a laser picosecond spectro-photo-chronometric complex is described, with which the studies were carried out. In Section VI a list of major publications is given. In the end, contact data of IRE employees who performed the study is presented.

I.   Intensive intrinsic picosecond stimulated emission of GaAs (hereinafter referred to as s-emission).

  1. Reversible picosecond change of bleaching (increasing transparency) spectrum of GaAs and therefore of the density of electron-hole plasma (EHP) - a sign of appearance of the picosecond stimulated emission during picosecond pumping [1,2][*] ,▲,●.

  2. Abnormal (picosecond) threshold emission of GaAs; its spectrum; the energy of its spectral components as a function of energy monopulse pumping and the delay between the two pump pulses [3*,▲,●].

  3. Area of light amplification in the spectrum of fundamental light absorption in photo-pumped GaAs [4*,▲,●,5]. The threshold of appearance [3*,▲,●] and anisotropy of the s-emission [6°].

  4. Picosecond "flare-up" [4*,▲,●,7] and exponential relaxation of s-emission, determined by EHP cooling [7,8]. Sub-gigawatt intensity of s-emission [9°].

  5. The slowing of picosecond stimulated radiative recombination of charge carriers at increasing of the diameter of photo pumped region [8].

  6. Characteristic for the stimulated emission dependence of the spectrum of s-emission on the active region diameter and on the pump picosecond pulse energy [10].

  7. "Universal" dependence of the longwave boundary of the s-emission spectrum on the energy density of s-emission due to renormalization of the band gap caused by Coulomb interaction of charge carriers (RBGC) [11].

  8. Stimulated Raman scattering (SRS) of s-emission and picosecond pumping, which occurs with the participation of optical plasmons [11,12]. This proves the activity of s-emission  in relation to the SRS.

  9. Nonlinear dynamics of long-wavelength edge of s-emission spectrum [13].

  10. Oscillating dependence of the moment of the beginning of s-emission flare-up on the energy of its photon [14].

  11.  Bistable self-modulation of s-emission spectrum – a new modification of the effect of competition and switching of spectral modes (CSSM) [14].

  12. Mutually matched self-modulation of characteristics of s-emission emerging from the end of the sample [15°].

II.   Electron-hole plasma (EHP) threshold state, supported by s-emission.

  1. Universal residual bleaching of GaAs and threshold state of the EDP at the end of s-emission [3,4] *,▲,●.

  2. Overthreshold state of the  EHP during s-emission [4*,▲,●,5].

  3. The relationship between the density of the EHP and its temperature at overthreshold and threshold states [2*,▲,●,11,16*,▲,●].

  4. Reversible picosecond change of the density and temperature of EHP [2*,▲,●] and of GaAs bleaching [1*,▲,●].

  5. An abnormal dependence of reversible threshold bleaching of GaAs on the pump photon energy. Influence of GaAs prebleaching on reversible change in its transparency [17▲,●].

  6. A single parameter, i.e., the EHP density, determines: (a) distribution of electrons between the valleys, (b) narrowing of the band gap width due to Coulomb interaction of charge carriers in Γ-valley, and (c) energy of the optical plasmon [11].

III.    S-emission-created picosecond depletion of the populations of energy levels of non-equilibrium electrons.

  1. LO-phonon oscillations in the spectrum of fundamental light absorption in GaAs, displaying the translation in the conduction band of the population depletion created by s-emission at the bottom of the zone [18°].

  2. "LO-phonon correlation" between the spectrum of s-emission and self-modulation of the light absorption spectrum in GaAs [6°].

  3. Similarity of self-modulation spectra of s-emission and light absorption [14].

  4. Amplification of energy transport of electrons with emission of LO-phonons, leading to modulation of the dependence of bleaching (consequently, EHP density) on the pumping photon energy ħωĺő [19]. For the formation of such a modulation is essential that EHP is  in overthreshold state.

  5. The influence of the energy transport of electrons with radiation of LO-phonons on the amplitude, width and long-wavelength edge of the s-emission spectrum, including appearance of modulation of the specified spectrum parameters’ dependence on the energy ħωĺő [19,20]. Herewith the modulation of the long-wavelength edge of the s-emission spectrum shows the modulation of the band gap width due to interaction of electrons with LO-phonons, whose density oscillates with ħωĺő.

  6. The limit value of the s-emission spectrum width in high-quality crystal as a function of the pump photon energy [20].

IV.    Picosecond oscillations of population depletion of nonequilibrium electron energy levels, arising in s-emission field and creating s-emission modulation. Self-synchronization of the oscillations. (More detailed information is given immediately below, as well as a list of received confirmations of this representation.)

The distribution of electrons in the lower part of the conduction band in a highly pumped thin GaAs layer is not like the Fermi one but is oscillatory. The depletions of inverse populations of energy levels, which are “burned” by spectral modes of s-emission, oscillate. The frequency of oscillations is determined, according to perturbation theory, by the s-emission intensity. Oscillations are synchronized in such a way as to ensure that their amplitude–phase–frequency characteristic provided detailed equilibrium of the transitions of electrons between their states. These transitions are an integral part of the stimulated Raman scattering (SRS) of spectral modes of s-emission. Since SRS processes are bound to be correlated for the above-mentioned detailed equilibrium, all these processes can be included in the class of multiwave mixing in nonlinear optics. The above-described oscillations of the populations naturally lead to the modulation of s-emission. The same oscillations of populations are transferred upward in the conduction band for detailed equilibrium upon electron–LO-phonon interaction, which leads to self-modulation of the fundamental absorption of light in GaAs. The height to which oscillations are translated depends on the degree of screening of the electron–LO-phonon interaction by charge carriers, i.e., on the density of the latter.

  1. Mutually-matched self-modulation of the s-emission characteristics, specified in section I, paragraph 11.

  2. Self-modulation of the absorption spectrum of the probing picosecond light pulse [21°], periodic in the spectrum [22°], in time [23°], and pump energy variation [24].

  3. Experimental amplitude-phase-frequency response of absorption self-modulation   [25°].

  4. Adapted analytical expression of the perturbation theory, satisfactorily describing the experimental dependence of the frequency of population depletion self-oscillations on s-emission intensity [9°].

  5. Oscillations of the absorption of the probing (p) picosecond light pulse with a fixed photon energy caused by interaction between p-pulse and s-emission [26].

  6. Self-synchronization of those modulations of electron energy level populations, that are generated by: (a) a picosecond probing light pulse and a spectral component of s-emission, (b) different spectral components of s-emission [27].

  7. Transitions of carriers between energy levels that occur during SRS of s-emission spectral components [9°,14].

  8. Signs of the formation of domain structure at synchronization of population modulation [27].

V.    Scientific equipment for experiments

Experiments are carried out on the laser picosecond-range spectral-photo-chronometrical complex with automatic system of measuring and processing physical parameters. In its original form, the complex was manufactured in SCLI VSU. After the last essential upgrade (April 2012), the complex is composed of the following components.

  • Driving YAG-laser PL PDP1-300 ("SynchroTech", Russia), which generates single pulses of wavelength = 1.064 µm, with controlled repetition rate and duration varied in the range T = 22 - 32 ps. Pulse energy instability  2%, duration T < 2 ps.

  • Amplifier of pulses generated by the driving laser, total energy gain ~102.

  • Optical frequency doublers for amplified pulses.

  • Two optical parametric oscillators (OPO) on LiNbO3 with temperature wavelength adjustment. For certain experiments, a third OPO with angular wavelength adjustment is additionally installed. The first two OPO are pumped with pulses of double frequency (wavelength = 0.532 µm), the third OPO – with pulses of = 1.064 µm. Pulses generated by each OPO are passed through separate channels and focused on a single pot of sample. These pulses are used for various pumping, for probing in “pump-probe” experiments, for EHP heating by means of intraband light absorption, etc. During experiments, time delay of sample irradiation by pulse, pulse wavelength in the range 0.35 - 2.0 µm and its energy are adjusted independently for each channel. Pulse duration (FWHM) 10 ps.

  • Spectrograph SpectraPro-2500i, able to operate in dispersion adding mode by spectral measurements and in dispersion subtraction mode by envelope (chronogram) measurements of separate spectrum components of picosecond light pulse. The latter mode ensures that the duration of emission component at spectrograph output is the same as at the input.

  • CCD-camera “PIXIS”, mounted at the second output slit of the first stage of double spectrograph. Allows instantaneous measurements of integrated-over-time spectrum of ultrashort optical emission. Measurement resolution from 0.3 nm (in 160 nm-wide range) to 0.05 nm (in the range of 30 nm width). For measurements in dispersion adding mode, photomultiplier is mounted at the output slit of the second stage of spectrograph.

  • Streak-camera PS-1/S1, that works together with CCD-camera “CoolSNAP”, is connected to the second output slit of double spectrograph and allows to measure chronograms of picosecond light pulse components, selected by spectrograph, with resolution no worse than 2 ps. Dynamic range of such measurements is 10 to 30, depending on light wavelength and pulse duration. Jitter (sweep start instability) is 4.5 ps, and it is  automatically compensated online by data acquisition. Streak-camera PS-1/S1 is designed and manufactured by Prokhorov General Physics Institute of RAS.

  • System of automatic registration and control, where: (a) physical quantities are measured and processed online, measurement accuracy estimated, and the results are delivered to imaging facilities; (b) light pulse delay lines, shutters of pulse propagation channels, spectrograph SpectraPro-2500i, two CCD-cameras ("PIXIS" and "CoolSNAP"), and photomultiplier are controlled. All these functions are realized with a special interface and a powerful computer program.

The complex gives the following possibilities. 1) Various kinds of sample pumping, including combined, synchronous or with adjustable time delay (no worse than 0.3 ps precision), by three pulses with specially adjusted photon energies and with various light intensity and various dimensions of focus spot on the sample. 2) Instantaneous measurement of time-integrated spectrum of ultrashort emission. The latter is particularly necessary when investigated feature preserves its spectral position on duration of emission pulse, and herewith experiment conditions require multiple spectrum measurements. 3) Measurements of variations of optical absorption, transparency and reflection during and after sample pumping. Measurements are carried out by pump-probe method in two variants. In the first variant, variations of probing pulse energy and its time-integrated spectrum, caused by sample pumping, are measured. In the second variant, chronogram of the whole probing pulse or of some of its spectral components is measured. 4) Measurements of chronograms of separate spectral components of intrinsic emission of sample. These chronograms also allow us to reconstruct time evolution of spectrum of ultra-short intrinsic emission.

Eventually, the complex provides a rare combination of unique technical possibilities for: ultrafast creation of powerful stimulated emission in GaAs with various parameters, simultaneous excitation of ultrafast processes of interaction of the emission with semiconductor, diversified optical investigation of these processes. And all that practically without heating the crystal lattice.

Note that before designing the streak-camera PS-1/S1 in Prokhorov GPI RAS, together with the scientists of this institute we had to lead joint study of accuracy of picosecond light pulse measurements by streak-cameras. Non-trivial methods and results of this study are published in [28]. 

VI.    The list of cited articles employees IRE RAS.

1.        I.L. Bronevoi, R.A. Gadonas, V.V. Krasauskas, T.M. Lifshits, A.S. Piskarskas, M.A. Sinitsyn, B.S. Yavich. JETP Lett., 42, ą8, 395 (1985).

2.        I.L. Bronevoi, S.E. Kumekov, V.I. Perel. JETP Lett., 43, ą8, 473 (1986).

3.        N.N. Ageeva, I.L. Bronevoi, E.G. Dyadyushkin, B.S. Yavich. JETP Lett., 48, ą5, 276 (1988).

4.        N.N. Ageeva, I.L. Bronevoi, E.G. Dyadyushkin, V.A. Mironov, S.E. Kumekov, V.I. Perel’. Sol. St. Commun., 72, 625 (1989).

5.        I.L. Bronevoi, A.N. Krivonosov, T.A. Nalet. Sol. St. Commun. 98, 903 (1996).

6.        N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov, S.E. Kumekov, S.V. Stegantsov. Semiconductors, 36, 136 (2002).

7.        N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov. JETP, 2013, Vol. 116, No. 4, pp. 551–557

8.        I.L. Bronevoi, A.N. Krivonosov. Semiconductors, 32, 484 (1998). In the article on page 543, right column, line 4 from top, in the expression (1) erroneously printed μe = µh ≈ Eg, while should be μe – µh ≈ Eg.

9.        N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov. Semiconductors, 44, 1121 (2010).

10.   I.L. Bronevoi, A.N. Krivonosov. Semiconductors, 32, 479 (1998).

11.   N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov. Semiconductors, 35, 67 (2001).

12.   I.L. Bronevoi, A.N. Krivonosov, V.I. Perel’. Sol. St. Commun., 94, 363 (1995).

13.   N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov. Semiconductors - in print.

14.   N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov. JETP, 117, No. 2, 191 (2013).

15.   N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov, S.E. Kumekov, T.A. Nalet, S.V. Stegantsov. Semiconductors, 39, 650 (2005).

16.   N.N. Ageeva, V.B. Borisov, I.L. Bronevoi, V.A. Mironov, S.E. Kumekov, V.I. Perel, B.S. Yavich, R. Gadonas. Sol. St. Com., 75, 167 (1990).

17.   N.N. Ageeva, I.L. Bronevoi, V.A. Mironov, S.E. Kumekov, V.I. Perel’. Sol. St. Com., 81, 969 (1992).

18.   I.L. Bronevoi, A.N. Krivonosov, V.I. Perel’. Sol. St. Commun., 94, 805 (1995).

19.   I.L. Bronevoi, A.N. Krivonosov. Semiconductors, 33, 10 (1999).

20.   N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov. Semiconductors, 46, 921 (2012).

21.   N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov, S.V. Stegantsov. Semiconductors, 40, 785 (2006).

22.   N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov, T.A. Nalet, S.V. Stegantsov. Semiconductors, 41, 1398 (2007).

23.   N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov, T.A. Nalet. Semiconductors, 42, 1037 (2008).

24.   N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov. Semiconductors, 44, 1285 (2010).

25.   N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov. Semiconductors, 42, 1395 (2008).

26.   N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov. JETP, 120, 664 (2015).

27.   N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov. Semiconductors, 50, 1312 (2016).

28.   N.N. Ageeva, I.L. Bronevoi, D.N. Zabegaev, A.N. Krivonosov, N.S. Vorob’ev, P.B. Gornostaev, V.I. Lozovoi, M.Ya. Schelev. Instrum. Exp. Tech., 54 (4), 548 (2011).

29.   N.N. Ageeva, I.L. Bronevoi, R. Gadonas, S.E. Kumekov, V.A. Mironov, V.I. Perel, B.S. Yavich. Lasers and ultrafast Processes, 4, 116 (1991).

30.   N.N. Ageeva, I.L. Bronevoi, S.E. Kumekov, V.A. Mironov, V.I. Perel' in: Mode-Locked Lasers and Ultrafast Phenomena, G.B.Altshuler, Editor, Proc. SPIE. 1842, 70 (1992) (Review).

31.   N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov, S.E. Kumekov, V.I. Perel. Bulletin of the Russian Academy of Sciences: Physics, 58, ą7, 89 (1994).

32.   N.N. Ageeva, I.L. Bronevoi, A.N. Krivonosov, D.N. Zabegaev. Physica Status Solidi C. V.8 (4), 1211 (2011).

Senior researcher, Ph.D.
N.N. Ageeva - ann@cplire.ru
Senior researcher, Ph.D.
A.N. Krivonosov - kan@cplire.ru
Junior researcher, D.N. Zabegaev – dimst@mail.ru

Principal researcher, Dr.Sci.
I.L. Bronevoi - bil@cplire.ru
.: +7 (495) 629 34 04

[*], ▲, ●, ° The results marked with the above icons are presented respectively in a brief interim reviews: [29], [30], [31], [32].

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