Generation of Complex Optical Pulse
Sequences by Multiple Comb Shaping
Dmitry Pestov, Vadim V. Lozovoy and Marcos Dantus
Optical pulse sequences, with con- trollable time delays and shapes,
are an important class of waveforms
used for autocorrelation and cross-correlation measurements, pump-probe
and coherent control experiments,
multidimensional nonlinear spectroscopy, etc. Arbitrary waveform generation requires the modulation of phase,
amplitude and even polarization of the
field. ;ere has been a growing interest
in simplifying pulse-train synthesis using limited degrees of freedom to control the spectral phase and amplitude of
the field by shapers with a single-mask
spatial light modulator (SLM). 1-3
Here, we introduce an intuitive and
versatile technique, called multiple independent comb shaping (MICS), which
enables generation of complex optical
pulse sequences via phase-only shaping
of the input laser spectrum. 4 Rather
than trying to reconstruct the Fourier
spectrum, which requires both phase
and amplitude modulation, we interlace
the spectral phase functions for each of
the sub-pulses.
For example, the technique allows
us to obtain intensity and interferometric autocorrelation traces without
splitting and overlapping beams. It also
enables straightforward and independent manipulation of the spectral phase
for every sub-pulse in the programmed
waveform. A pulse train consisting of
three di;erently shaped pulses is easily
obtained using phase-only MICS. ;e
interferometric cross-correlation of such
a pulse train is obtained by generating
an additional (fourth) transform-limited
pulse, which is scanned in time while
the second harmonic generation signal
is recorded. ;e time delay tuning is
accomplished through pulse shaping by
changing the slope of the linear phase
function for the fourth pulse.
(a)
Comb 1
Comb 2
ϕ = (ω-ωc)τ
Comb 1 + Comb 2
Phase
ϕ = 0
+
Phase
Phase =
0
Frequency
Frequency
0
Frequency
(b)
Wavelength [nm]
430
MICA
405
380
- 40 - 20 0 20 40
Delay [fs]
Delay [fs]
- 40 - 20 0 20
(c)
Intensity [arb. units]
1.0
0.5
0.0
- 40 40
i-MICA
MICA i-MICA
21. 8 fs
Delay [fs]
- 20 0 20 40
0.0
(d)
Intensity [arb. units]
-300
1.0
0.5
-200
-100
Delay [fs]
0
100
200
300
(a) Multiple independent comb shaping (MICS) concept applied to the generation of a pair of
delayed optical pulses. The two pulses, one at zero delay and the other at delay τ, are created by encoding a piecewise phase mask across the spectrum. This phase is an alternating
superposition of continuous phase functions applied to two independent combs that sample
the spectrum. (b) Intensity and interferometric autocorrelation spectrograms. (c) Spectrally
integrated intensity and interferometric autocorrelations. (d) Complex waveform generation: a
3+ 1 pulse sequence, with the ;rst pulse having third-order dispersion of -5000 fs3, the second
with second-order dispersion of +200 fs2, and the third transform limited (TL). The fourth TL
pulse is scanned to produce a cross-correlation trace. The data shown in (b-d) were acquired
using a Ti:sapphire femtosecond oscillator, producing 15-fs pulses (central wavelength, 810
nm), and a 4f-shaper with a one-dimensional single-mask 640-pixel liquid-crystal SLM. Phase
distortions in the original pulse were eliminated using MIIPS. 5
To summarize, MICS allows the
straightforward design of pulse trains
for which the time delay, spectral
phase function and relative phase are
determined, even using a shaper with a
single-mask, one-dimensional SLM. ;is
last point is especially valuable for amplified laser systems, when the pulse shaper
is placed before a regenerative amplifier
and therefore amplitude modulation of
the seeded spectrum is undesirable.
Dmitry Pestov, Vadim V. Lozovoy and Marcos Dantus ( dantus@msu.edu) are with the department of
chemistry, Michigan State University, East Lansing,
Mich., U.S.A.
References
1. A. M. Weiner et al. J. Opt. Soc. Am. A 10, 1112-20 (1993).
2. J. C. Vaughan et al. Opt. Lett. 30, 323-5 (2005).
3. E. Frumker and Y. Silberberg. J. Opt. Soc. Am. B 24,
2940-7 (2007).
4. D. Pestov et al. Opt. Express 17, 14351-61 (2009).
5. Y. Coello et al. J. Opt. Soc. Am. B-Opt. Phys. 25, A140-
A150 (2008).
