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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 14 — Jul. 5, 2010
  • pp: 15155–15168
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Interaction of a single-cycle laser pulse with a bound electron without ionization

Ufuk Parali and Dennis R. Alexander  »View Author Affiliations


Optics Express, Vol. 18, Issue 14, pp. 15155-15168 (2010)
http://dx.doi.org/10.1364/OE.18.015155


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Abstract

In this paper, interaction of an ultrashort single-cycle pulse (USCP) with a bound electron without ionization is reported for the first time. For a more realistic mathematical description of USCPs, Hermitian polynomials and combination of Laguerre functions are used for two different single cycle excitation cases. These single cycle pulse models are used as driving functions for the classical approach to model the interaction of a bound electron with an applied electric field. A new novel time-domain technique was developed for modifying the classical Lorentz damped oscillator model in order to make it compatible with USCP excitation. This modification turned the Lorentz oscillator model equation into a Hill-like function with non-periodic time varying damping and spring coefficients. Numerical results are presented for two different excitation models and for varying spring and damping constants. Our two driving model excitations provide quite different time response of the bound electron. Different polarization response will subsequently result in relative differences in the time dependent index of refraction.

© 2010 OSA

1. Introduction

Ultrashort light pulse research has led to the creation of laser systems generating pulses only a few cycles in duration [1

1. A. Couairon, J. Biegert, C. P. Hauri, W. Kornelis, F. W. Helbing, U. Keller, and A. Mysyrowicz, “Self-compression of ultrashort laser pulses down to one optical cycle by filamentation,” J. Mod. Opt. 53(1–2), (2006).

]. Now that these ultrashort few-cycle EM pulses exist experimentally, the need for mathematical models to describe these short pulse interactions with matter becomes very important [2

2. M. A. Porras, “Nonsinusoidal few-cycle pulsed light beams in free space,” J. Opt. Soc. Am. B 16(9), 1468 (1999). [CrossRef]

]. There is a growing need to model and to understand the interaction of single ultrashort pulses or a train of ultrashort pulses with matter below the point where strong field effects dominate. This need is driven by the advances made in femtosecond (fs) and attosecond (as) laser technologies. Applications of these ultra short pulses range from free space communications, 3D depth profiling in biological samples, optical communication, high resolution/precision atomic and molecular scale imaging, high speed electronics and optoelectronics in terahertz (THz) regime, behavior of electrons in quantum structures, relativistic physics, high-energy physics, astrophysics to medical applications. Furthermore, ultrafast few cycle lasers are expected to be a promising solution to probe the fastest events in atomic, molecular, biochemical, and solid state systems due to their unique property of being the shortest controlled bursts of energy ever developed [3

3. P. B. Corkum and F. Krausz, “Attosecond science,” Nat. Phys. 3(6), 381–387 (2007). [CrossRef]

11

11. K. Akimoto, Properties and Applications of ultrashort electromagnetic mono- and sub- cycle waves. Journal ofthe Physical Society of Japan, Vol. 65, No. 7, 2020–2032, 1996.

].

Basic physics of the pulse-matter interaction depends strongly on the ratio of the pulse duration and the characteristic response time of the medium (as well as on the pulse intensity and energy). This ratio is the key term in the polarization response of the medium. The goal of this study is to provide insight in the linear polarization response of dispersive materials to ultrashort single cycle pulses. This paper is concerned with the case where the electric field strength is low enough to not produce ionization. Since the energy is below the ionization threshold of the medium, there is not any plasma effect during the interaction of the applied field with the matter. Understanding the linear polarization response is extremely crucial in order to formulate a realistic field integral. This realistic field integral will provide a more realistic propagation model of optical pulses through dispersive media [12

12. R. M. Joseph, S. C. Hagness, and A. Taflove, “Direct time integration of Maxwell’s equations in linear dispersive media with absorption for scattering and propagation of femtosecond electromagnetic pulses,” Opt. Lett. 16(18), 1412–1414 (1991). [CrossRef] [PubMed]

24

24. D. Hovhannisyan, “Propagation of a femtosecond laser pulse of a few optical oscillations in a uniaxial crystal,” Microw. Opt. Technol. Lett. 36(4), 280–285 (2003). [CrossRef]

]. The interaction of an ultra short pulse with matter involves the interaction of the incident electric field with the electrons of the material. In this study, classical approaches to this problem are modified for solving the interaction of a single-cycle ultrashort laser pulse with a bound electron without ionization.

2. Mathematical model

In order to make an original contribution for the analysis of the interaction of an ultrashort single-cycle pulse (USCP) with a bound electron without ionization, first it is necessary to find a realistic model for a USCP. Such pulses have a rather different structure from conventional modulated quasi-monochromatic signals with a rectangular or Gaussian envelope [25

25. A. B. Shvartsburg, Single-cycle waveforms and non-periodic waves in dispersive media (exactly solvable models). Physics – Uspekhi, Vol. 41, No. 1, 77–94, 1998.

28

28. A. B. Shvartsburg, Impulse Time-Domain Electromagnetic of Continuos Media. Birkhauser Verlag, Boston, 1999.

]. Due to the following main reasons associated with USCPs, combination of Laguerre functions and Hermitian polynomials (Mexican Hat) are used in this study for modeling applied EM field:
  • i) Arbitrary transient steepness: The rising and the falling times of the signal can be essentially unequal.
  • ii) Varying zero spacing: The distances between zero-crossing points may be essentially unequal.
  • iii) Both the waveform envelope and its first spatial and temporal derivatives are continuous.
  • iv) Arbitrary envelope asymmetry: USCP waveforms can be classified conventionally for two groups.
    • 1) The sharply defined zero-crossing point at the pulse leading edge as initial point (combination of Laguerre functions).
    • 2) The sharply defined narrow maximum against a background of comparatively long tails (Hermitian polynomials – Mexican Hat) [25

      25. A. B. Shvartsburg, Single-cycle waveforms and non-periodic waves in dispersive media (exactly solvable models). Physics – Uspekhi, Vol. 41, No. 1, 77–94, 1998.

      28

      28. A. B. Shvartsburg, Impulse Time-Domain Electromagnetic of Continuos Media. Birkhauser Verlag, Boston, 1999.

      ].
Although delta function or the Heaviside step function are widely used, they assume zero signal duration and zero relaxation time. These assumptions are not suitable for modeling the waveform of a USCP. There are some other more realistic models, such as modulated Gaussian or rectangular transients, but these models assume equally spaced zeros which is not suitable for a USCP, neither [25

25. A. B. Shvartsburg, Single-cycle waveforms and non-periodic waves in dispersive media (exactly solvable models). Physics – Uspekhi, Vol. 41, No. 1, 77–94, 1998.

28

28. A. B. Shvartsburg, Impulse Time-Domain Electromagnetic of Continuos Media. Birkhauser Verlag, Boston, 1999.

].

The combination of Laguerre functions for defining the spatiotemporal profile of a USCP is defined as Em(t)=B(Lm(t)Lm+2(t)) where Lm(x)=(exp(x/2)/m!)dmdxm[exp(x)xm] is a single Laguerre function with order m and x=(tzc1)/t0. Here, c is the velocity of light in vacuum, z is the propagation direction and t0 is the time scale of the pulse. In this study, the combination of 2nd and 4th order Laguerre functions are used to define a single USCP:
E2(α)=exp((7.5α)2)[124α4+1524α352α2+2α],
(1)
where the phase term is defined as α=(tϕzc1)/t0 in which ϕ is the initial phase [Fig. 1(a)
Fig. 1 (a) Applied Laguerre USCP with pulse duration τp = 8x10−16. (b) 1st derivative of the LaguerreUSCP.
].

Figure 1(b) shows the first derivative of the applied field and it is clearly seen that the analytical expression E(α) in Eq. (1) satisfies the conditions of arbitrary transient steepness and arbitrary envelope asymmetry. From Fig. 1(a), it is also clearly seen that it satisfies the condition of varying zero spacing for a USCP. In addition to these, time profile of the Laguerre USCP is almost fulfilling the integral property:
0E2(α)dα=0.
(2)
For the Hermitian (Mexican Hat) USCP [Fig. 2(a)
Fig. 2 (a) Applied Hermitian USCP with pulse duration τp=8x10−15, (b) 1st derivative of the Hermitian USCP.
], the following definition is used:
E(α)=(1α2)exp(α2/2).
(3)
Figure 2(b) illustrates that the Hermitian pulse satisfies the above concerns.

In addition to the question how to formulate ultrashort single cycle transients, it is also natural to ask how these pulses propagate in optical medium. In this study, USCP means the smallest possible single cycle piece (unity source) of a wave packet. It is the part of an actual carrier field and does not contain any other carrier fields in itself. For a USCP, it is difficult to introduce the concept of an envelope and it is not possible to define a group velocity. For such short pulses the distinction between carrier oscillations and slowly varying envelope (SVE), which have two different temporal scales that are peculiar to quasi-monochromatic pulses, becomes diffuse or meaningless [22

22. H. Xiao and K. E. Oughstun, “Failure of the group velocity description for ultrawideband pulse propagation in a casually dispersive, absorptive dielectric,” J. Opt. Soc. Am. B 16(10), 1773 (1999). [CrossRef]

,29

29. J. E. Rothenberg, “Space-time focusing: Breakdown of the slowly varying envelope approximation in the self-focusing of femtosecond pulses,” Opt. Lett. 17(19), 1340 (1992). [CrossRef] [PubMed]

31

31. M. D. Crisp, “Propagation of small-area pulses of coherent light through a resonant medium,” Phys. Rev. A 1(6), 1604–1611 (1970). [CrossRef]

]. Jumping from many cycle optical waves to single cycle optical pulses in dealing with light-matter interaction, the mathematical treatments should be revised. The traditional analysis of pulsed EM phenomena is questionable [25

25. A. B. Shvartsburg, Single-cycle waveforms and non-periodic waves in dispersive media (exactly solvable models). Physics – Uspekhi, Vol. 41, No. 1, 77–94, 1998.

28

28. A. B. Shvartsburg, Impulse Time-Domain Electromagnetic of Continuos Media. Birkhauser Verlag, Boston, 1999.

]. If the applied field is a USCP, the shortest possible field as explained above, then it is impossible to separate the applied source into pieces to find the effect of each part (or piece) by superposing as being suggested in the models explained in many fundamental textbooks [32

32. B. K. P. Scaife, Principles of Dielectrics, Oxford University Press, Oxford, 1989.

].

In order to understand the USCP-medium interaction phenomenon, we must acquire certain special features such as operating directly with Maxwell equations beyond the scope of Fourier representations [25

25. A. B. Shvartsburg, Single-cycle waveforms and non-periodic waves in dispersive media (exactly solvable models). Physics – Uspekhi, Vol. 41, No. 1, 77–94, 1998.

28

28. A. B. Shvartsburg, Impulse Time-Domain Electromagnetic of Continuos Media. Birkhauser Verlag, Boston, 1999.

]. Since the situations occur where the time scale of the pulse is equal or shorter than the relaxation time of the medium, material has no time to establish its response parameters during the essential part of the pulse continuance [23

23. A. L. Gutman, “Electrodynamics of short pulses for pulse durations comparable to relaxation times of a medium,” Dokl. Phys. 43(6), 343–345 (1998).

,33

33. A. L. Gutman, Passage of short pulse throughout oscillating circuit with dielectric in condenser. Ultra-Wideband, Short-Pulse Electromagnetics 4, Kluwer Academic / Plenum Publishers, New York, 1999.

36

36. A. B. Shvartsburg, G. Petite. Progress in Optics, Vol. 44 (Ed. E Wolf), p. 143, Elsevier Sci, 2002.

]. These parameters, which govern the polarization response of the media, change their values during the pulse continuance [23

23. A. L. Gutman, “Electrodynamics of short pulses for pulse durations comparable to relaxation times of a medium,” Dokl. Phys. 43(6), 343–345 (1998).

,33

33. A. L. Gutman, Passage of short pulse throughout oscillating circuit with dielectric in condenser. Ultra-Wideband, Short-Pulse Electromagnetics 4, Kluwer Academic / Plenum Publishers, New York, 1999.

]. Thus, solutions of Maxwell equations with time-dependent coefficients are required for the analysis of the wave dynamics [35

35. A. B. Shvartsburg, Optics of nonstationary media, Physics – Uspekhi, Vol. 48, No. 8, 797–823, 2005.

,36

36. A. B. Shvartsburg, G. Petite. Progress in Optics, Vol. 44 (Ed. E Wolf), p. 143, Elsevier Sci, 2002.

].

In our study, we consider an approach such that under a single USCP excitation, the change in the relative position of a bound electron to its parent atom without ionization will change the amplitude of the dipole in the atom and so forth the instantaneous polarization. As a result of this fluctuation in the polarization, the index of refraction will change in the duration of the single USCP excitation during which the propagation dynamics of the same applied USCP and the other USCPs coming after the first one will be evaluated. So physically, we consider a case where the medium is including the source. This is a common situation especially in optical communication. In addition to this, we can associate this approach to some diagnostic techniques in ultrafast optics such as pump-probe experiments where both pump and probe pulses propagate and evaluate the time varying physical parameters of the medium. But before diving into Maxwell equations, we have to figure out how the polarization response of the medium must be handled for the interaction of a USCP EM field with a bound electron. Understanding the polarization response of the material under the excitation of a USCP EM field is one of the most important, not clearly answered yet, core question of today and near future ultrafast laser engineering.

Polarization is a very crucial physical term, especially for optical communication, since it defines the change in the index of refraction in the material due to the applied field [23

23. A. L. Gutman, “Electrodynamics of short pulses for pulse durations comparable to relaxation times of a medium,” Dokl. Phys. 43(6), 343–345 (1998).

,33

33. A. L. Gutman, Passage of short pulse throughout oscillating circuit with dielectric in condenser. Ultra-Wideband, Short-Pulse Electromagnetics 4, Kluwer Academic / Plenum Publishers, New York, 1999.

,34

34. V. V. Daniel, Dielectric Relaxation. Academic Press, New York, 1967.

,37

37. K. S. Cole and R. H. Cole, “Dispersion and absorption in dielectrics,” J. Chem. Phys. 9(4), 341–351 (1941). [CrossRef]

,38

38. A. B. Djurišic and E. H. Li, “Modeling the index of refraction of insulating solids with a modified Lorentz oscillator model,” Appl. Opt. 37(22), 5291 (1998). [CrossRef]

]. In terms of permittivity, we can write index of refraction (for a nonmagnetic material) as:
n=(1+P(t)εoE(t))12,
(4)
where εo is the permittivity of free space, E(t) is the applied electric field, and P(t) is the electronic polarization. The polarization response of the medium gives the change in the index of refraction. This change or this polarization response affects the temporal and spatial evaluation of the propagating pulse [8

8. A. Couairon, M. Franco, A. Mysyrowicz, J. Biegert, and U. Keller, “Pulse self-compression to the single-cycle limit by filamentation in a gas with a pressure gradient,” Opt. Lett. 30(19), 2657–2659 (2005). [CrossRef] [PubMed]

,10

10. G. Steinmeyer, D. H. Sutter, L. Gallmann, N. Matuschek, and U. Keller, “Frontiers in Ultrashort Pulse Generation: Pushing the Limits in Linear and Nonlinear Optics,” Science 286(5444), 1507–1512 (1999). [CrossRef] [PubMed]

,39

39. S. P. Blanc, R. Sauerbrey, S. C. Rae, and K. Burnett, “Spectral blue shifting of a femtosecond laser pulse propagating through a high-pressure gas,” J. Opt. Soc. Am. 10(10), (1993).

41

41. C. B. Schaffer, Interaction of femtosecond laser pulses with transparent materials, Ph.D. Thesis. Harvard University, May 2001.

].

Fig. 3 Schematic representation of self modulation (pulse chirping). Although we are interested in the low intensity applied fields for linear polarization in this study, temporal dependence of the intensity profile of the applied field can still cause a temporal dependence in the refractive index [41].

The starting point of all these dynamics is the inhomogeneous wave equation:
2E(z,t)z21c022E(z,t)t2=μo2Pt2,
(5)
where the polarization is the source term of the governing differential equation. In order to find the polarization, we must find the oscillation field (displacement) of the bound electrons. According to the Lorentz damped forced oscillator model:
med2x(t)dt2+meγodx(t)dt+kox(t)=eE(t),
(6)
x(t) is the time dependent displacement or the oscillation field of a bound electron with respect to the applied field E(t), γo is the damping constant, ko is the spring constant of the material and me is the mass of electron.

For USCP excitation, unlike the long pulse excitation fields, the response (oscillation) of the electron must be handled in a different manner. Since, both due to the mass of inertia of the electron and the shortness of the USCP compared to the relaxation time of the medium, the electron will not sense the applied field exactly at the leading edge point of the pulse. The response of the electron to the applied field will increase gradually. During this sense, the electron will not follow the oscillation profile of the applied electric field. So, the oscillation field of the electron will not only have a difference in the phase but also will have a different time profile (time-dependency) with the applied field. In regular cases, if the applied field is in the form of ejwt time-dependency, then we assume that the oscillation of the electron will be in the same time-dependency form. In the literature, Lorentz oscillator model is directly used in ejwt time-dependency [42

42. K. E. Oughstun and G. C. Sherman, “Uniform asymptotic description of electromagnetic pulse propagation in a linear dispersive medium with absorption (the Lorentz medium),” J. Opt. Soc. Am. A 6(9), 1394–1420 (1989). [CrossRef]

]. But for a USCP excitation, not only the time-dependency ejwtis not valid, but also the oscillation field will have a different waveform than the applied field waveform (time-dependency). This means that, the x(t) term in Eq. (6), that is the oscillation field of the electron, will have a modified form of time-dependency with respect to the applied USCP. In order to define the modified function x(t), we developed a new time domain technique that we call “Modifier Function Approach”. In this approach, we define the oscillation field of the electron as the multiplication of the applied USCP with the modifier function:
x(t)=xo(t)E(t),
(7)
where xo(t) is the modifier function. It has a unit of (meter)2/volt which is equivalent to Coulomb*meter/Newton. So physically, modifier function defines dipole moment per unit force. Plugging Eq. (7) into Eq. (6), we obtain
med2(xo(t)E(t))dt2+meγod(xo(t)E(t))dt+ko(xo(t)E(t))=eE(t).
(8)
Performing the necessary calculations in Eq. (8), we obtain Eq. (10):
med2xo(t)dt2E(t)+2medxo(t)dtdE(t)dt+mexod2E(t)dt2+meγodxo(t)dtE(t)+meγoxo(t)dE(t)dt+koxo(t)E(t)=eE(t),
(9)
meE(t)d2xo(t)dt2+me(2dE(t)dt+γoE(t))dxo(t)dt+me(d2E(t)dt2+γodE(t)dt+komeE(t))xo(t)=eE(t)
d2xo(t)dt2+(2E(t)dE(t)dt+γo)dxo(t)dt+(1E(t)d2E(t)dt2+γoE(t)dE(t)dt+kome)xo(t)=eme.
(10)
We can briefly write Eq. (10) as:
d2xo(t)dt2+P(t)dxo(t)dt+Q(t)xo(t)=eme,
(11)
where
P(t)=2E(t)dE(t)dt+γo,
(12)
Q(t)=1E(t)d2E(t)dt2+γoE(t)dE(t)dt+kome.
(13)
It is seen at Eq. (11) that it has a similar form with a Hill type equation where for a regular Hill equation, P(t) and Q(t) terms are periodic and the right side is zero. A linear equation of this type occurs often when a system exhibiting periodic motion is perturbed in some way [43

43. L. N. Hand, and J. D. Finch, Analytical Mechanics. Cambridge University Press, 7th edition, Cambridge, 2008.

]. This type of equation was first derived by G.W. Hill to describe the effect of perturbations on the orbit of the Moon, and it occurs in many other places in physics, including the quantum motion of electrons in a periodic potential of a crystal [43

43. L. N. Hand, and J. D. Finch, Analytical Mechanics. Cambridge University Press, 7th edition, Cambridge, 2008.

]. The band theory of solids is based on a similar equation, as is the theory of propagating electromagnetic waves in a periodic structure [43

43. L. N. Hand, and J. D. Finch, Analytical Mechanics. Cambridge University Press, 7th edition, Cambridge, 2008.

]. Other applications include parametric amplifiers. Although P(t) and Q(t) terms are periodic in a Hill equation, in our case they are not. So, in our model, Eq. (11) is a Hill-like equation which has a dc source on its right side and a time-dependent damping coefficient (12) and a time-dependent spring coefficient (13) in terms of a damped forced oscillator model. The objective of Eq. (11) is to find the modifier function which can be then used to define the oscillation field (polarization response) of the material. Due to the time-dependent damping and spring coefficients, the modifier function is totally coupled with the time dependency or time profile of the applied field.

Equation (6) could also have been solved directly in the temporal domain, in which case we would have lost the analogy with the Hill-like equation. But the appropriateness of using the more complicated approach with the modifier function has solid physical reasons. In the case of a USCP excitation, the polarization response of the material is not unique all through the pulse continuance. Due to the shortness of the duration of the applied USCP comparing to the relaxation time of the bound electron, the interaction dynamics and the ability of the material to sense and follow the applied USCP field during its continuance will be completely different than the conventional matter-field interaction approach. In Eq. (6), physical parameters (damping and spring coefficients) are constant. However, the interaction dynamics will not be constant during the USCP excitation. So, in order to penetrate the effect of the applied field into the oscillator model via these physical parameters to have a better understanding of the oscillation response of the material under USCP excitation, we must find the definition of these physical parameters in terms of the applied field and the physical constants of the system (material). Equation (12) and Eq. (13) are these definitons. They are being used in Eq. (11) to find the modifier function which has been embedded into Eq. (6). The physical dimension of the modifier function is a dipole moment per unit force. It frames the time dependency and the phase delay of the oscillation field of the bound electron under USCP excitation.

3. Numerical results and discussions

In Fig. 4
Fig. 4 Bounded electron motion under Laguerre USCP excitation ((a), (c), (e), (g), (i)) and Hermitian USCP excitation ((b), (d), (f), (h), (j)) for various values of spring constant (ko) with a fixed damping constant (δo=1x1014).
, different interaction characteristics of Laguerre and Hermitian pulses are shown for a fixed, relatively low value of damping constant (δo=1x1014). Due to the definition: w0=kome, (me is the mass of electron, ko is the spring constant for bound electron), t he free oscillation frequency of material is in UV range for spring constant values of 4 N/m, 9 N/m, 325 N/m, 525 N/m [Figs. 4(a), 4(b), 4(c), 4(d), 4(e), 4(f), 4(g), 4(h)], 650 N/m [Fig. 8(b)
Fig. 8 Hermitian pulse excitation oscillations for damping constant: δo=1x1017
] and 750 N/m [Figs. 5(b)
Fig. 5 Laguerre pulse excitation oscillations for damping constant: δo=1x1016
, 8(c)]. For spring constant values of 1500 N/m [Fig. 5(c)], 2500 N/m [Figs. 4(i), 4(j)] and 7500 N/m [Fig. 8(d)], the free oscillation frequency is in X-ray range. As it is clearly seen in Fig. 4, the Hermitian interaction has a more tendency to oscillation than the Laguerre interaction for relatively low values of spring constant [see Figs. 4(a), 4(b), 4(c), 4(d)]. As the spring constant is increased, Laguerre interaction gains a more oscillatory profile [see Figs. 4(e), 4(g)] while the oscillation due to the Hermitian pulse interaction stabilizes and its time profile settles down into the inverted phase time profile of the excitation pulse (inverted Mexican Hat) [see Figs. 4(f), 4(h), 4(j)]. Here, the amplitude of oscillation or the amplitude of trembling-like motion of the electron is in the range of 10−20 m – 10−21 m which is in the scale of electron radius length. Finally, as the spring constant is increased to relatively higher values, the Laguerre interaction settles down into the inverted phase time profile of the excitation pulse, too (inverted Laguerre pulse) [see Fig. 4(i)]. Figure 4 shows a very clear distinction between the interaction characteristics of Laguerre and Hermitian USCPs until the spring constant is 2500 N/m (after this value, we obtain only the inverted phase time profile of the excitation source for the oscillation). The oscillation characteristics of bound electron under different single USCP sources originates from modifier function approach. The Hill-like equation, which is the result of the modification on the classic Lorentz damped oscillator model with the modifier function approach, causes the time varying physical parameters to come into play during the interaction process. Since these physical parameters (time varying damping and spring coefficients) are absolutely source dependent, they behave differently in the pulse duration of each different USCP source. As a result of this, we see different oscillation profiles for a bound electron under a single Laguerre and Hermitian USCP excitations.

For a damping constant value of 1x1017 (Fig. 8), very different oscillation behaviors are seen than the previuos cases (Fig. 4) of Hermitian pulse excitation. The most prominent feature in Figs. 8(a), 8(b) and 8(c) is the high frequency oscillation profile with a phase delay wrt. excitation pulse. In Fig. 8, spring constant is increased gradually from 8(a) to 8(c) while keeping the damping value constant. For a relatively low value of spring constant in Fig. 8(a), the main lobe and the trailing tail of the excitation pulse have almost no effect on the oscillation of the electron. The bound electron starts sensing the leading tail of the Hermitian excitation after a phase delay of 5 fs. In Fig. 9
Fig. 9 Hermitian pulse excitation modifier functions for damping constant: δo=1x1017
, the modifier function solutions for the Hermitian pulse excitation for Fig. 8 is shown. As it is clearly seen in Fig. 9(a), modifier function suppresses the interaction effect of main lobe and the trailing tail of Hermitian function. As a result of this, the bound electron starts sensing the excitation pulse with a phase delay [Fig. 8(a)] associated with the modifier function. Same behaviour of the modifier function is seen in Figs. 9(b) and 9(c), too. As a result of this, approximately 2fs phase delay occurs in Figs. 8(b) and 8(c). In Fig. 9(d), the type of modifier function is seen that gives a completely phase inverted time profile of the excitation pulse for the oscillation of the bound electron. In Fig. 8(d), the stabilized oscillation profile is seen as a result of this modifier function.

4. Conclusion

The results of this work indicate that if the applied field is a USCP, then it is not possible to separate the field into pieces to find the polarization effect of each part of the applied field on a bound electron since the USCP cannot be further broken down into separate pieces of the applied field. The traditional Fourier method of multiplying the Delta function response with the applied field and integrating (superposing) this product in time can only be used for SVE approximation which is not realistic for single cycle pulses of unity femtosecond and attosecond applied fields. In a USCP case, the Lorentz oscillator model must be modified in order to find the polarization effect of a single USCP. Since a USCP is extremely broadband, it is not realistic to use a center frequency in the calculations as is done in the Fourier series expansion approach. Results in this work are presented on the transient response of the system during the USCP duration without switching to frequency domain. In order to accomplish this mathematically, we developed a new technique we label as the “Modifier Function Approach”. The modifier function is embedded in the classic Lorentz damped oscillator model and by this way, we upgrade the oscillator model so that it is compatible with the USCP on its right side as the driving force. Results of this work also provide a new modified version of the Lorentz oscillator model for ultrafast optics. The results also indicate that the time response of the two models used to represent the USCP can alter the time dependent polarization of the material as it interacts with a single cycle pulse.

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J. Itatani, J. Levesque, D. Zeidler, H. Niikura, H. Pépin, J. C. Kieffer, P. B. Corkum, and D. M. Villeneuve, “Tomographic imaging of molecular orbitals,” Nature 432(7019), 867–871 (2004). [CrossRef] [PubMed]

7.

G. Krauss, S. Lohss, T. Hanke, A. Sell, S. Eggert, R. Huber, and A. Leitenstorfer, “Synthesis of a single cycle of light with compact erbium-doped fibre technology,” Nat. Photonics 4(1), 33–36 (2010). [CrossRef]

8.

A. Couairon, M. Franco, A. Mysyrowicz, J. Biegert, and U. Keller, “Pulse self-compression to the single-cycle limit by filamentation in a gas with a pressure gradient,” Opt. Lett. 30(19), 2657–2659 (2005). [CrossRef] [PubMed]

9.

Y. Yan, E. B. Gamble Jr, and K. A. Nelson, “Impulsive stimulated scattering: General importance in femtosecond laser pulse interactions with matter, and spectroscopic applications,” J. Chem. Phys. 83(11), 5391 (1985). [CrossRef]

10.

G. Steinmeyer, D. H. Sutter, L. Gallmann, N. Matuschek, and U. Keller, “Frontiers in Ultrashort Pulse Generation: Pushing the Limits in Linear and Nonlinear Optics,” Science 286(5444), 1507–1512 (1999). [CrossRef] [PubMed]

11.

K. Akimoto, Properties and Applications of ultrashort electromagnetic mono- and sub- cycle waves. Journal ofthe Physical Society of Japan, Vol. 65, No. 7, 2020–2032, 1996.

12.

R. M. Joseph, S. C. Hagness, and A. Taflove, “Direct time integration of Maxwell’s equations in linear dispersive media with absorption for scattering and propagation of femtosecond electromagnetic pulses,” Opt. Lett. 16(18), 1412–1414 (1991). [CrossRef] [PubMed]

13.

S. L. Dvorak, D. G. Dudley. Propagation of ultrawideband electromagnetic pulses through dispersive media. IEEE Transaction of Electromagnetic Compatibility, Vol. 37. No. 2, May 1995.

14.

S. A. Kozlov and S. V. Sazanov, “Nonlinear propagation of optical pulses of a few oscillations duration in dielectric media,” Sov. Phys. JETP 84(2), 221–228 (1997). [CrossRef]

15.

H. Wilkelmsson, J. H. Trombert, and J. F. Eloy, “Dispersive and dissipative medium response to an ultrashort pulse: A green’s function approach,” Phys. Scr. 52(1), 102–107 (1995). [CrossRef]

16.

P. Kinsler and G. H. C. New, “Few-cycle pulse propagation,” Phys. Rev. A 67(2), 023813 (2003). [CrossRef]

17.

J. F. Eloy, and F. Moriamez, Spectral analysis of EM ultrashort pulses at coherence limit. Modelling. SPIE Intense Microwave and Particle Beams III, Vol. 1629, 1992.

18.

J. F. Eloy and H. Wilhelmsson, “Response of a bounded plasma to ultrashort pulse excitation,” Phys. Scr. 55(4), 475–477 (1997). [CrossRef]

19.

M. Pietrzyk, I. Kanattsikov, and U. Bandelow, “On the propagation of vector ultrashort pulses,” J. Nonlinear Math. Phys. 15(2), 162–170 (2008). [CrossRef]

20.

B. Macke and B. Segard, “Propagation of light pulses at a negative group velocity,” Eur. Phys. J. D 23, 125–141 (2003). [CrossRef]

21.

Q. Zou and B. Lu, “Propagation properties of ultrashort pulsed beams with constant waist width in free space,” Opt. Laser Technol. 39(3), 619–625 (2007). [CrossRef]

22.

H. Xiao and K. E. Oughstun, “Failure of the group velocity description for ultrawideband pulse propagation in a casually dispersive, absorptive dielectric,” J. Opt. Soc. Am. B 16(10), 1773 (1999). [CrossRef]

23.

A. L. Gutman, “Electrodynamics of short pulses for pulse durations comparable to relaxation times of a medium,” Dokl. Phys. 43(6), 343–345 (1998).

24.

D. Hovhannisyan, “Propagation of a femtosecond laser pulse of a few optical oscillations in a uniaxial crystal,” Microw. Opt. Technol. Lett. 36(4), 280–285 (2003). [CrossRef]

25.

A. B. Shvartsburg, Single-cycle waveforms and non-periodic waves in dispersive media (exactly solvable models). Physics – Uspekhi, Vol. 41, No. 1, 77–94, 1998.

26.

Z. Wang, Z. Zhang, Z. Xu, and Q. Lin, “Space-time profiles of an ultrashort pulsed Gaussian beam,” IEEE J. Quantum Electron. 33(4), (1997).

27.

A. B. Shvartsburg, Time-Domain Optics of Ultrashort Waveforms. Clarendon Press, Oxford, 1996.

28.

A. B. Shvartsburg, Impulse Time-Domain Electromagnetic of Continuos Media. Birkhauser Verlag, Boston, 1999.

29.

J. E. Rothenberg, “Space-time focusing: Breakdown of the slowly varying envelope approximation in the self-focusing of femtosecond pulses,” Opt. Lett. 17(19), 1340 (1992). [CrossRef] [PubMed]

30.

H. Kumagai, S. H. Cho, K. Ishikawa, K. Midorikawa, M. Fujimoto, S. Aoshima, and Y. Tsuchiya, “Observation of the comples propagation of a femtosecond laser pulse in a dispersive transparent bulk material,” J. Opt. Soc. Am. 20(3), (2003).

31.

M. D. Crisp, “Propagation of small-area pulses of coherent light through a resonant medium,” Phys. Rev. A 1(6), 1604–1611 (1970). [CrossRef]

32.

B. K. P. Scaife, Principles of Dielectrics, Oxford University Press, Oxford, 1989.

33.

A. L. Gutman, Passage of short pulse throughout oscillating circuit with dielectric in condenser. Ultra-Wideband, Short-Pulse Electromagnetics 4, Kluwer Academic / Plenum Publishers, New York, 1999.

34.

V. V. Daniel, Dielectric Relaxation. Academic Press, New York, 1967.

35.

A. B. Shvartsburg, Optics of nonstationary media, Physics – Uspekhi, Vol. 48, No. 8, 797–823, 2005.

36.

A. B. Shvartsburg, G. Petite. Progress in Optics, Vol. 44 (Ed. E Wolf), p. 143, Elsevier Sci, 2002.

37.

K. S. Cole and R. H. Cole, “Dispersion and absorption in dielectrics,” J. Chem. Phys. 9(4), 341–351 (1941). [CrossRef]

38.

A. B. Djurišic and E. H. Li, “Modeling the index of refraction of insulating solids with a modified Lorentz oscillator model,” Appl. Opt. 37(22), 5291 (1998). [CrossRef]

39.

S. P. Blanc, R. Sauerbrey, S. C. Rae, and K. Burnett, “Spectral blue shifting of a femtosecond laser pulse propagating through a high-pressure gas,” J. Opt. Soc. Am. 10(10), (1993).

40.

G. P. Agrawal and N. A. Olsson, “Self-phase modulation and spectral broadening of optical pulses in semiconductor laser amplifiers,” IEEE J. Quantum Electron. 25(11), 2297–2306 (1989). [CrossRef]

41.

C. B. Schaffer, Interaction of femtosecond laser pulses with transparent materials, Ph.D. Thesis. Harvard University, May 2001.

42.

K. E. Oughstun and G. C. Sherman, “Uniform asymptotic description of electromagnetic pulse propagation in a linear dispersive medium with absorption (the Lorentz medium),” J. Opt. Soc. Am. A 6(9), 1394–1420 (1989). [CrossRef]

43.

L. N. Hand, and J. D. Finch, Analytical Mechanics. Cambridge University Press, 7th edition, Cambridge, 2008.

OCIS Codes
(000.3860) General : Mathematical methods in physics
(260.5430) Physical optics : Polarization
(320.2250) Ultrafast optics : Femtosecond phenomena
(320.5550) Ultrafast optics : Pulses
(320.7090) Ultrafast optics : Ultrafast lasers
(320.7120) Ultrafast optics : Ultrafast phenomena

ToC Category:
Ultrafast Optics

History
Original Manuscript: May 6, 2010
Revised Manuscript: June 17, 2010
Manuscript Accepted: June 18, 2010
Published: June 30, 2010

Citation
Ufuk Parali and Dennis R. Alexander, "Interaction of a single-cycle laser pulse with a bound electron without ionization," Opt. Express 18, 15155-15168 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-14-15155


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References

  1. A. Couairon, J. Biegert, C. P. Hauri, W. Kornelis, F. W. Helbing, U. Keller, and A. Mysyrowicz, “Self-compression of ultrashort laser pulses down to one optical cycle by filamentation,” J. Mod. Opt. 53(1–2), (2006).
  2. M. A. Porras, “Nonsinusoidal few-cycle pulsed light beams in free space,” J. Opt. Soc. Am. B 16(9), 1468 (1999). [CrossRef]
  3. P. B. Corkum and F. Krausz, “Attosecond science,” Nat. Phys. 3(6), 381–387 (2007). [CrossRef]
  4. A. Zewail, “Femtochemistry: atomic-scale dynamics of the chemical bond,” J. Phys. Chem. A 104(24), 5660–5694 (2000). [CrossRef]
  5. H. Niikura, F. Légaré, R. Hasbani, A. D. Bandrauk, M. Y. Ivanov, D. M. Villeneuve, and P. B. Corkum, “Sub-laser-cycle electron pulses for probing molecular dynamics,” Nature 417(6892), 917–922 (2002). [CrossRef] [PubMed]
  6. J. Itatani, J. Levesque, D. Zeidler, H. Niikura, H. Pépin, J. C. Kieffer, P. B. Corkum, and D. M. Villeneuve, “Tomographic imaging of molecular orbitals,” Nature 432(7019), 867–871 (2004). [CrossRef] [PubMed]
  7. G. Krauss, S. Lohss, T. Hanke, A. Sell, S. Eggert, R. Huber, and A. Leitenstorfer, “Synthesis of a single cycle of light with compact erbium-doped fibre technology,” Nat. Photonics 4(1), 33–36 (2010). [CrossRef]
  8. A. Couairon, M. Franco, A. Mysyrowicz, J. Biegert, and U. Keller, “Pulse self-compression to the single-cycle limit by filamentation in a gas with a pressure gradient,” Opt. Lett. 30(19), 2657–2659 (2005). [CrossRef] [PubMed]
  9. Y. Yan, E. B. Gamble, and K. A. Nelson, “Impulsive stimulated scattering: General importance in femtosecond laser pulse interactions with matter, and spectroscopic applications,” J. Chem. Phys. 83(11), 5391 (1985). [CrossRef]
  10. G. Steinmeyer, D. H. Sutter, L. Gallmann, N. Matuschek, and U. Keller, “Frontiers in Ultrashort Pulse Generation: Pushing the Limits in Linear and Nonlinear Optics,” Science 286(5444), 1507–1512 (1999). [CrossRef] [PubMed]
  11. K. Akimoto, Properties and Applications of ultrashort electromagnetic mono- and sub- cycle waves. Journal ofthe Physical Society of Japan, Vol. 65, No. 7, 2020–2032, 1996.
  12. R. M. Joseph, S. C. Hagness, and A. Taflove, “Direct time integration of Maxwell’s equations in linear dispersive media with absorption for scattering and propagation of femtosecond electromagnetic pulses,” Opt. Lett. 16(18), 1412–1414 (1991). [CrossRef] [PubMed]
  13. S. L. Dvorak, D. G. Dudley. Propagation of ultrawideband electromagnetic pulses through dispersive media. IEEE Transaction of Electromagnetic Compatibility, Vol. 37. No. 2, May 1995.
  14. S. A. Kozlov and S. V. Sazanov, “Nonlinear propagation of optical pulses of a few oscillations duration in dielectric media,” Sov. Phys. JETP 84(2), 221–228 (1997). [CrossRef]
  15. H. Wilkelmsson, J. H. Trombert, and J. F. Eloy, “Dispersive and dissipative medium response to an ultrashort pulse: A green’s function approach,” Phys. Scr. 52(1), 102–107 (1995). [CrossRef]
  16. P. Kinsler and G. H. C. New, “Few-cycle pulse propagation,” Phys. Rev. A 67(2), 023813 (2003). [CrossRef]
  17. J. F. Eloy, and F. Moriamez, Spectral analysis of EM ultrashort pulses at coherence limit. Modelling. SPIE Intense Microwave and Particle Beams III, Vol. 1629, 1992.
  18. J. F. Eloy and H. Wilhelmsson, “Response of a bounded plasma to ultrashort pulse excitation,” Phys. Scr. 55(4), 475–477 (1997). [CrossRef]
  19. M. Pietrzyk, I. Kanattsikov, and U. Bandelow, “On the propagation of vector ultrashort pulses,” J. Nonlinear Math. Phys. 15(2), 162–170 (2008). [CrossRef]
  20. B. Macke and B. Segard, “Propagation of light pulses at a negative group velocity,” Eur. Phys. J. D 23, 125–141 (2003). [CrossRef]
  21. Q. Zou and B. Lu, “Propagation properties of ultrashort pulsed beams with constant waist width in free space,” Opt. Laser Technol. 39(3), 619–625 (2007). [CrossRef]
  22. H. Xiao and K. E. Oughstun, “Failure of the group velocity description for ultrawideband pulse propagation in a casually dispersive, absorptive dielectric,” J. Opt. Soc. Am. B 16(10), 1773 (1999). [CrossRef]
  23. A. L. Gutman, “Electrodynamics of short pulses for pulse durations comparable to relaxation times of a medium,” Dokl. Phys. 43(6), 343–345 (1998).
  24. D. Hovhannisyan, “Propagation of a femtosecond laser pulse of a few optical oscillations in a uniaxial crystal,” Microw. Opt. Technol. Lett. 36(4), 280–285 (2003). [CrossRef]
  25. A. B. Shvartsburg, Single-cycle waveforms and non-periodic waves in dispersive media (exactly solvable models). Physics – Uspekhi, Vol. 41, No. 1, 77–94, 1998.
  26. Z. Wang, Z. Zhang, Z. Xu, and Q. Lin, “Space-time profiles of an ultrashort pulsed Gaussian beam,” IEEE J. Quantum Electron. 33(4), (1997).
  27. A. B. Shvartsburg, Time-Domain Optics of Ultrashort Waveforms. Clarendon Press, Oxford, 1996.
  28. A. B. Shvartsburg, Impulse Time-Domain Electromagnetic of Continuos Media. Birkhauser Verlag, Boston, 1999.
  29. J. E. Rothenberg, “Space-time focusing: Breakdown of the slowly varying envelope approximation in the self-focusing of femtosecond pulses,” Opt. Lett. 17(19), 1340 (1992). [CrossRef] [PubMed]
  30. H. Kumagai, S. H. Cho, K. Ishikawa, K. Midorikawa, M. Fujimoto, S. Aoshima, and Y. Tsuchiya, “Observation of the comples propagation of a femtosecond laser pulse in a dispersive transparent bulk material,” J. Opt. Soc. Am. 20(3), (2003).
  31. M. D. Crisp, “Propagation of small-area pulses of coherent light through a resonant medium,” Phys. Rev. A 1(6), 1604–1611 (1970). [CrossRef]
  32. B. K. P. Scaife, Principles of Dielectrics, Oxford University Press, Oxford, 1989.
  33. A. L. Gutman, Passage of short pulse throughout oscillating circuit with dielectric in condenser. Ultra-Wideband, Short-Pulse Electromagnetics 4, Kluwer Academic / Plenum Publishers, New York, 1999.
  34. V. V. Daniel, Dielectric Relaxation. Academic Press, New York, 1967.
  35. A. B. Shvartsburg, Optics of nonstationary media, Physics – Uspekhi, Vol. 48, No. 8, 797–823, 2005.
  36. A. B. Shvartsburg, G. Petite. Progress in Optics, Vol. 44 (Ed. E Wolf), p. 143, Elsevier Sci, 2002.
  37. K. S. Cole and R. H. Cole, “Dispersion and absorption in dielectrics,” J. Chem. Phys. 9(4), 341–351 (1941). [CrossRef]
  38. A. B. Djurišic and E. H. Li, “Modeling the index of refraction of insulating solids with a modified Lorentz oscillator model,” Appl. Opt. 37(22), 5291 (1998). [CrossRef]
  39. S. P. Blanc, R. Sauerbrey, S. C. Rae, and K. Burnett, “Spectral blue shifting of a femtosecond laser pulse propagating through a high-pressure gas,” J. Opt. Soc. Am. 10(10), (1993).
  40. G. P. Agrawal and N. A. Olsson, “Self-phase modulation and spectral broadening of optical pulses in semiconductor laser amplifiers,” IEEE J. Quantum Electron. 25(11), 2297–2306 (1989). [CrossRef]
  41. C. B. Schaffer, Interaction of femtosecond laser pulses with transparent materials, Ph.D. Thesis. Harvard University, May 2001.
  42. K. E. Oughstun and G. C. Sherman, “Uniform asymptotic description of electromagnetic pulse propagation in a linear dispersive medium with absorption (the Lorentz medium),” J. Opt. Soc. Am. A 6(9), 1394–1420 (1989). [CrossRef]
  43. L. N. Hand, and J. D. Finch, Analytical Mechanics. Cambridge University Press, 7th edition, Cambridge, 2008.

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