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2-kW Average Power CW Phase-Conjugate Solid-State Laser

18 Jun 2007-IEEE Journal of Selected Topics in Quantum Electronics (IEEE)-Vol. 13, Iss: 3, pp 473-479

AbstractWe have demonstrated stable operation of a 2-kW Yb:YAG phase-conjugate master oscillator power amplifier (PC-MOPA) laser system with a loop phase-conjugate mirror (LPCM). This is the first demonstration of a continuous wave (CW)-input LPCM MOPA operating at a power greater than 1 kW with a nearly diffraction-limited output beam. The single-pass beam quality incident on the LPCM varied with the specific operating conditions, but it was typically ~20 times diffraction-limited (XDL). The measured beam quality with an MOPA output power of 1.65 kW was 1.3 XDL.

Topics: Laser beam quality (57%)

Summary (2 min read)

Introduction

  • More recently, the interest in high-power solid-state lasers has broadened to include new applications requiring continuous wave (CW) or quasi-CW operation.
  • A. A. Betin was with Raytheon Space and Airborne Systems, Raytheon, El Segundo, CA 90245 USA.
  • The physical basis of the FWM is the fact that the presence of two interfering high-power laser beams (a signal beam and a reference beam) in the absorbing medium produces a spatially varying temperature distribution, and consequently, a spatially varying refractive index or hologram in the nonlinear medium.
  • First, an LPCM can function over a wide peak- and average-power dynamic range.

II. SYSTEM ARCHITECTURE

  • The signal beam originates from a commercial Yb:YAG master oscillator [12].
  • Relay-imaging telescopes are an important element of the MOPA system, and they are used throughout the amplifier chain and also within the LPCM.
  • The amplifiers employ zigzag signal propagation, which has long been known to mitigate the effects of fast-axis thermal lensing in face-cooled laser slabs.
  • Following the nonlinear cell (NC) is a Faraday isolator favoring propagation in the counterclockwise direction, but that is slightly detuned to allow a few percent of the initial beam to pass through in the clockwise direction toward the LPCM amplifier A4.
  • Beams 1 and 3 are made to overlap in the nonlinear medium, where the interference between the beams produces a spatially varying refractive index pattern (i.e., a hologram) in the nonlinear medium.

III. LPCM

  • The basic operation of an LPCM has been described earlier [10], [11], and a detailed description of the present LPCM is also available [13].
  • The LPCM amplifier provides the gain required to compensate the resonator losses at the outcoupler and the other optical elements.
  • The third term indicates how the refractive index responds to the intensity grating formed by the two writing beams, including the time dependence of the thermal gratings that is governed by the thermal diffusivity of the nonlinear medium, χ. Equation (1) shows that, for a given absorption, the two key material parameters are (dn/dT ) and χ.
  • Additional medium-selection parameters include a sufficiently high boiling temperature, a low chemical reactivity, and preferably a minimal health hazard.
  • So far, this discussion has focused on the energetics of the LPCM.

IV. EXPERIMENTAL RESULTS

  • The fully integrated PC-MOPA system was operated for extended time periods ∼30 min or more, exhibiting stable outputbeam parameters and excellent beam quality.
  • During these measurements, the near-field intensity distribution approximately filled a rectangular aperture having dimensions of 5.5× 4.5 mm2.
  • Each power amplifier was represented by an exponential dependence of the gain G on extracted power Pex as given by G = G0 exp(−Pex/Psat), using measured values for the small- signal gain G0 and the saturation power Psat.
  • The functional dependence of the reflected power for the LPCM on its operating conditions was derived from a separate model that matched all of their LPCM data rather well.

V. CONCLUSION

  • The output beam quality was quite good, and the authors present data showing a beam quality of ∼1.3 XDL.
  • The output power achieved in this research was primarily limited by the performance of the power amplifiers and not by the LPCM.
  • Hence, the authors believe scaling to significantly higher powers ∼25 kW or more will be possible with improved amplifiers.

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IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 13, NO. 3, MAY/JUNE 2007 473
2-kW Average Power CW Phase-Conjugate
Solid-State Laser
Yuri A. Zakharenkov, Todd O. Clatterbuck, Vladimir V. Shkunov, Alexander A. Betin, David M. Filgas,
Eric P. Ostby, Friedrich P. Strohkendl, David A. Rockwell, Member, IEEE, and Robert S. Baltimore
Abstract—We have demonstrated stable operation of a 2-kW
Yb:YAG phase-conjugate master oscillator power amplifier (PC-
MOPA) laser system with a loop phase-conjugate mirror (LPCM).
This is the first demonstration of a continuous wave (CW)-input
LPCM MOPA operating at a power greater than 1 kW with a
nearly diffraction-limited output beam. The single-pass beam qual-
ity incident on the LPCM varied with the specific operating condi-
tions,butitwastypically20 times diffraction-limited (XDL). The
measured beam quality with an MOPA output power of 1.65 kW
was 1.3 XDL.
Index Terms—Beam quality, continuous wave (CW) high-energy
laser, laser amplifiers, phase-conjugate mirror (PCM), power in the
bucket, solid-state laser.
I. INTRODUCTION
O
VER THE PAST 25 years, it has been clearly established
that fairly simple devices based on nonlinear optical phase
conjugation (NOPC) are capable of eliminating many problems
arising from thermal loads in high-peak power pulsed solid-state
lasers [1]–[3]. Present purposes can be served by simply stating
that reciprocal phase aberrations induced in an optical beam by
any medium can, in principle, be compensated by reflecting the
aberrated beam off a phase-conjugate mirror (PCM) and passing
the beam back through the aberrating medium. The output beam
will have the same beam quality as the initial unaberrated beam.
More recently, the interest in high-power solid-state lasers
has broadened to include new applications requiring continuous
wave (CW) or quasi-CW operation. Single-rod [4] and multiple-
disk [5] configurations have been reported with output powers
>1 kW (but with significantly reduced power for operation with
M
2
< 10). Two-rod [6] and slab [7] lasers operating at greater
than 400 W have also been described. Finally, the “heat capacity
laser” [8] reached record power of 31.3 kW, but only for 1–2 s of
continuous operation, while operation for much longer times [9]
was reported at 19 kW.
These CW or quasi-CW systems are not very compatible with
stimulated Brillouin scattering (SBS) phase conjugation (which
Manuscript received December 5, 2006; revised March 21, 2007. This work
was supported in part by High Energy Laser Joint Technology Office and in part
by Space and Airborne Systems, Raytheon, El Segundo, CA 90245.
Y. A. Zakharenkov, T. O. Clatterbuck, V. V. Shkunov, D. M. Filgas,
F. P. Strohkendl, D. A. Rockwell, and R. S. Baltimore are with Raytheon
Space and Airborne Systems, El Segundo, CA 90245 USA (e-mail:
yuri_a_zakharenkov@raytheon.com).
E. P. Ostby is with Raytheon Space and Airborne Systems, El Segundo, CA
90245 USA and also with California Institute of Technology, Pasadena, CA
91125 USA.
A. A. Betin was with Raytheon Space and Airborne Systems, Raytheon, El
Segundo, CA 90245 USA. He is now with the General Atomics, San Diego, CA
92121 USA.
Digital Object Identifier 10.1109/JSTQE.2007.896565
has been utilized in the vast majority of pulsed phase-conjugate
(PC) solid-state lasers) for two main reasons. First, their output
powers are much lower than the peak powers achieved by even
modest pulsed solid-state lasers, making it difficult to reach the
SBS threshold. Second, even very low absorption coefficients in
the nonlinear medium can produce unacceptably high thermal
loads at required operational power levels.
In view of these limitations to the applicability of SBS phase
conjugation, we began developing an alternative NOPC archi-
tecture approximately 10 years ago. This alternative architec-
ture is called a loop phase-conjugate mirror (LPCM), and this
name is derived from the fact that the nonlinear medium is in-
corporated into a loop resonator [10]. Our LPCM exploits a
thermal nonlinearity, whereby four-wave mixing (FWM) oc-
curs in an absorbing medium. The physical basis of the FWM
is the fact that the presence of two interfering high-power laser
beams (a signal beam and a reference beam) in the absorbing
medium produces a spatially varying temperature distribution,
and consequently, a spatially varying refractive index or holo-
gram in the nonlinear medium. This hologram can be “read” by
a third beam, thereby producing PC replica of the input signal
beam.
This LPCM offers several important advantages over SBS
in high-average power laser applications. First, an LPCM can
function over a wide peak- and average-power dynamic range.
This allows operation at power levels ranging from low values of
a few watts to high values of many kilowatts. Second, an LPCM
offers broad wavelength coverage, and finally, it is compatible
with lasers producing short coherence lengths (1 cm or less).
Several low-power experimental LPCM demonstrations have
been reported [10], [11]; these demonstrations are consistent
with the advantages asserted earlier. However, to our knowl-
edge, there have been no prior reports of LPCMs that might
be used in high-power CW phase-conjugate master oscillator
power amplifier (PC-MOPA) laser systems.
This paper represents the first successful demonstration of
a quasi-CW solid state PC-MOPA laser system producing a
nearly diffraction-limited beam with power >1 kW. Section II
describes the overall system architecture, while Section III de-
scribes the LPCM, and Section IV summarizes our experimental
results.
II. S
YSTEM ARCHITECTURE
Fig. 1 shows a schematic diagram of our double-pass PC-
MOPA. The signal beam originates from a commercial Yb:YAG
master oscillator [12]. The master oscillator (MO) output passes
through a Faraday isolator and an outcoupler into the amplifier
1077-260X/$25.00 © 2007 IEEE

474 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 13, NO. 3, MAY/JUNE 2007
Fig. 1. Schematic diagram of the PC MOPA system.
beamline that comprises one or more Yb:YAG amplifier slabs
(A1–A3).
Relay-imaging telescopes are an important element of the
MOPA system, and they are used throughout the amplifier chain
and also within the LPCM. In addition, high-power variable
apertures are located at the foci of the relay optics to function as
spatial filters. Each of these imaging telescopes is schematically
shown as a single pair of lenses in the figure, but in some cases,
a telescope can also contain cylindrical optics (not shown) that
might be used to change the aspect ratio of the beam.
The imaging optics and their spatial-filtering capability play
an important function in the MOPA system. First, the optics
reimage the pupil from one stage to the next, ensuring that
the beam exiting one amplifier is delivered to the next amplifier
with high efficiency. Consequently, during the initial signal pass
through the amplifiers, the imaging telescopes avoid any signif-
icant loss of aberration information at the hard apertures that
are distributed along the beam path. Such loss of information
would degrade the possible phase conjugation fidelity.
Second, during both passes through the amplifier chain, the
spatial-filtering capability prevents a large fraction of the highly
divergent amplified spontaneous emission (ASE) from entering
successive amplification stages and extracting power from the
amplifiers or causing a parasitic oscillation.
The amplifier transverse dimensions correspond to an aspect
ratio of 18:1, which approximately matches the far-field diver-
gence (10
×0.6
) of typical fast-axis-collimated laser diode
arrays. This allows coupling the output from a 2-D laser diode
array into the slab with a single lens. At the required power
levels, the thermal lensing in the thin (fast) axis of a slab is very
high if light would be traveling along the axis of the slab. The
amplifiers employ zigzag signal propagation, which has long
been known to mitigate the effects of fast-axis thermal lensing
in face-cooled laser slabs.
The high aspect ratio amplifier slabs induce only slight de-
polarization during operation. Hence, we can achieve the out-
coupling function by inserting a Faraday rotator (FR) into the
amplifier/LPCM path (for example, between A1 and A2, as
shown in the figure). This rotator is double-passed by the sig-
nal beam. Consequently, the second-pass output polarization is
orthogonal to that of the first-pass beam. A common polarizing
beam splitter then separates the MOPA output beam from the
orthogonally polarized oscillator input beam.
The LPCM is also schematically shown in Fig. 1. The aber-
rated first-pass beam, denoted as beam 1, enters the LPCM
and passes through the cell that contains the nonlinear medium.
Fig. 2. Schematic diagram of nonlinear cell (NC) indicating labels on the four
interacting beams.
Following the nonlinear cell (NC) is a Faraday isolator favor-
ing propagation in the counterclockwise direction, but that is
slightly detuned to allow a few percent of the initial beam to
pass through in the clockwise direction toward the LPCM am-
plifier A4. This amplifier raises the power of the beam, now
denoted as beam 3, to the same level as beam 1. This attenu-
ation of beam 1 is important to ensure that beam 1 does not
extract too much power from A4—system efficiency is greatly
enhanced if the counterpropagating beam extracts most of the
power from the amplifiers. Beams 1 and 3 are made to over-
lap in the nonlinear medium, where the interference between
the beams produces a spatially varying refractive index pattern
(i.e., a hologram) in the nonlinear medium.
This hologram provides the feedback necessary to initiate
oscillation in the counterclockwise direction for the loop laser
resonator, which is formed by the amplifier A4, the hologram
as a resonator mirror, and several folding mirrors, as shown in
Fig. 1. The beam generated by this laser oscillation is denoted
as beam 2 in the vicinity of the NC and as beam 4 just after it
is diffracted back into the loop by the dynamic hologram of the
NC (see Fig. 2). Under a wide range of operating conditions,
the loop output beam 2 is the conjugate of the loop input beam
1. Most of beam 2 passes through the NC to form the LPCM
output, thereby functioning as the conjugate seed that initiates
the second pass through the amplifier chain.
III. LPCM
The basic operation of an LPCM has been described ear-
lier [10], [11], and a detailed description of the present LPCM
is also available [13]. The key components of the LPCM are
the NC, the LPCM amplifier A4, and the isolator (see Fig. 1).
Diffraction by the hologram grating in the NC allows it to func-
tion simultaneously as a resonator mirror, a transverse-mode
selector, and an outcoupler. For typical operating conditions,
the hologram diffraction efficiency is designed to be low, ap-
proximately a few percent, so, the Q-factor of the ring-laser
resonator is low. The LPCM amplifier provides the gain re-
quired to compensate the resonator losses at the outcoupler and
the other optical elements. It also provides power for the PC
output beam. The isolator prohibits ring-laser oscillations in the
forward (clockwise) direction, preserving the optical power for
the backward (counter-clockwise) PC beam.
A variety of nonlinear processes can be used in the LPCM NC.
In this paper, we employ a thermal nonlinearity, and the nonlin-
ear medium is an absorbing liquid. The hologram arises from

ZAKHARENKOV et al.: 2-KW AVERAGE POWER CW PHASE-CONJUGATE SOLID-STATE LASER 475
the fact that the spatially varying intensity distribution produced
by the interference of beams 1 and 3 (the two beams incident
from the right-hand side in Fig. 2) induces a spatially varying
temperature distribution in the absorbing liquid, which leads to
a spatially varying index distribution through the temperature
dependence of the refractive index.
The choice of an optimum liquid is essential and is based on
the trade study reported in [14]. Consider the situation in which
a pair of plane waves propagating in an absorbing medium
forms a refractive index grating having a spatial period Λ.The
steady-state diffraction efficiency η for such a thermal grating
follows from the model presented in [14], [15], and for the
approximation of weak diffraction, the diffraction efficiency is
given by
η =(αL)
2
Λ
2
2πλ
2
2

dn
dT
2
I
1
I
3
(1)
where α is the liquid absorption coefficient at the signal wave-
length, L is the thickness of the absorbing layer in the direction
of the beam propagation, λ is the signal wavelength, and I
1
and I
3
are intensities of the writing beams. The first term in (1)
combined with the final terms (the beam intensities) represent
the total power absorbed in the medium, while the second term
(in square brackets) implicitly embodies the system geometry
(beam-crossing angle) within the grating spatial period. The
third term indicates how the refractive index responds to the
intensity grating formed by the two writing beams, including
the time dependence of the thermal gratings that is governed by
the thermal diffusivity of the nonlinear medium, χ. Equation (1)
shows that, for a given absorption, the two key material param-
eters are (dn/dT ) and χ. These parameters drive the material
selection. Additional medium-selection parameters include a
sufficiently high boiling temperature, a low chemical reactiv-
ity, and preferably a minimal health hazard. Typical candidate
nonlinear media include acetone, toluene, carbon tetrachloride,
benzene, and carbon disulfide.
We have developed a model to predict the LPCM per-
formance under typical operating conditions. The model as-
sumes that, for a broad range of extracted optical powers
P
ext
, the loop amplifier gain G, follows exponential saturation
G = G
0
exp(P
ext
/P
sat
), characterized by a saturation power
P
sat
. The model further assumes that the grating reflectivity η
obeys (1), specifically that it is proportional to the product of
the powers of two writing beams as η = νP
1
P
3
. The effective
parameters for the loop amplifier—the small signal gain G
0
and the saturation parameter P
sat
—depend on the diode pump
power and the input beam alignment. The slope ν for the grating
efficiency is controlled by the sizes of the writing beams as well
as the cell geometry and operating conditions.
By simply invoking power balance per round-trip for both
propagation directions, one can derive explicit relations for the
output power P
2
and a threshold P
thr
with respect to the input
power P
1
; for the limit of interest, corresponding to a low grating
efficiency η 1, these expressions can be simplified to
P
2
P
sat
T ln
P
1
P
thr
,P
thr
=
exp
τ
F
P
2
sat
G
0
T
τ
F
ν
(2)
where T is the loop round-trip transmission and τ
F
is the Fara-
day transmission of beam 1 in the forward (clockwise) direc-
tion. The loop reflectivity reaches a maximum for an input sig-
nal power P
1
= eP
thr
2.71P
thr
, yielding a reflected power
P
max
2
= TP
sat
, which is determined by only two parameters—
the amplifier saturation power and the linear round-trip loss.
Experiments demonstrate excellent agreement between the pre-
dictions of (2) and measured data [13].
So far, this discussion has focused on the energetics of the
LPCM. However, given that the function of the LPCM is to
achieve phase conjugation, it is appropriate to consider how
the loop resonator can be optimized such that the dominant
transverse mode of the resonator is the PC replica of the input
signal beam. Detailed studies indicate that the grating in the
NC possesses a fine-structured fringe pattern that preferentially
reflects the PC portion of beam 2 back into the loop resonator,
thereby allowing the PC mode to have the lowest threshold.
Several measures can be taken to discriminate in favor of the PC
mode against noise components [16]–[20] including reducing
the size of beam 3 relative to beam 1 and inserting a spatial filter
that efficiently transmits the input signal beam but blocks much
of the spatial noise.
IV. E
XPERIMENTAL RESULTS
The fully integrated PC-MOPA system was operated for ex-
tended time periods 30 min or more, exhibiting stable output-
beam parameters and excellent beam quality. Fig. 3 shows the
calculated and measured far-field intensity distributions in the
focal plane of a 530-mm lens while the PC-MOPA system was
producing 1.65-kW output power. The corresponding gains
and extracted powers of the individual power amplifiers are
summarized in Table I.
During these measurements, the near-field intensity distri-
bution approximately filled a rectangular aperture having di-
mensions of 5.5 ×4.5 mm
2
. The left-hand side of Fig. 3 in-
dicates the calculated far-field intensity distribution for such
a near-field aperture, assuming a uniform near-field intensity
and planar phase over the entire aperture. The measured far-
field intensity distribution is also shown for comparison, and
it is obvious that the two distributions are very similar. This
is quantified in the power-in-the-bucket (PIB) curves shown in
Fig. 3. The blue curve represents the calculated PIB curve for
the uniform intensity/phase distribution, while the red curve
represents the experimental measurements. At the 50% power
level, the experimental curve is 1.3 XDL. Note that far-field
power measurements through a series of hard apertures show
that >90% of the total PC-MOPA output power is contained
within the field of view of the video camera and analysis system
that was used to generate the far-field data in Fig. 3.

476 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 13, NO. 3, MAY/JUNE 2007
Fig. 3. Calculated and measured far-field intensity profiles at the focal plane of
a lens with an effective focal length of 530 mm. Calculation assumes a uniform
intensity and phase over an entire 5.5 ×4.5 mm
2
aperture. Power-in-the-bucket
curve shows that the measured PC MOPA output beam quality is 1.3 XDL at
the 50% power level. The beam size, or D value, used in the calculated PIB is
5 mm.
TABL E I
G
AIN AND TOTAL DOUBLE-PASS EXTRACTED POWER FROM THE
NONOPTIMIZED YB:YAG POWER AMPLIFIERS WHILE OPERATING THE
OVERALL SYSTEM AT 1.65-KWOUTPUT POWER
Subsequent data were taken at higher powers. Fig. 4 shows a
temporal record of the MOPA output power 2 kW over a time
period of approximately 10 min.
In addition to the overall system, we quantified the perfor-
mance of the LPCM [13]. It suffices here to note that the ex-
perimental characterization of the two nonlinear components
of the operating LPCM—the thermal cell and the saturated
amplifier—both performed as expected, based on the aforemen-
tioned model.
We compared the performance of the overall PC-MOPA sys-
tem with the predictions of a model that uses measured charac-
teristics for each element and the transmission losses between
elements to calculate the power for both the first and second
pass, between each pair of amplifiers, and at the final output
beam. Each power amplifier was represented by an exponential
dependence of the gain G on extracted power P
ex
as given by
G = G
0
exp(P
ex
/P
sat
), using measured values for the small-
Fig. 4. PC MOPA operation with output power exceeding 2 kW.
Fig. 5. Experimental points and model (curve) results for MOPA output power
versus master oscillator input power.
signal gain G
0
and the saturation power P
sat
. Although this
gain-saturation equation is identical to the one discussed earlier
in connection with the LPCM amplifier, the quantitative values
of the parameters G
0
and P
sat
are different, as they are also
for the various power amplifiers. This approximation provides
a good match with the empirical data for limited intervals of
extraction, and it is consistent with a more rigorous standard
saturation model for the gain media. The functional dependence
of the reflected power for the LPCM on its operating condi-
tions was derived from a separate model that matched all of our
LPCM data rather well.
Fig. 5 compares the PC-MOPA model with experimental re-
sults, where the overall output power is plotted against the input
power E
0
of the master oscillator light incident on the outcou-
pler. For these experiments, E
0
was varied by a factor of 5
with relatively minor changes in overall system performance.
For these calculations, the polarization outcoupler transmission
is taken as 95% both ways, and the transmission between the
amplifiers is taken as 80% for the first pass and 90% for the
second pass; the first and second pass spatial filter transmis-
sions between A3 and the LPCM were taken as 75% and 100%,
respectively.
V. C
ONCLUSION
We have generated up to 2 kW of quasi-CW average laser
power with a nearly diffraction-limited beam quality using a
double-pass PC-MOPA architecture incorporating an LPCM.
The output beam quality was quite good, and we present data

ZAKHARENKOV et al.: 2-KW AVERAGE POWER CW PHASE-CONJUGATE SOLID-STATE LASER 477
showing a beam quality of 1.3 XDL. The output power
achieved in this research was primarily limited by the perfor-
mance of the power amplifiers and not by the LPCM. Hence, we
believe scaling to significantly higher powers 25 kW or more
will be possible with improved amplifiers.
A
CKNOWLEDGMENT
The authors would like to thank N. P. Davis, J. J. Ichkhan,
R. G. Hegg, T. Matsuoka, S. McGanty, R. A. Reeder, D. Reinard,
S. Sorbel, R. Zamudio, and R. Zhou for their excellent support.
R
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with controllable nonlinear mirrors,” Bull. Acad. Sci. USSR Phys. Series,
vol. 53, no. 8, pp. 52–59, 1989.
[20] A. A. Betin and A. V. Kirsanov, “Selection of phase conjugate wave in an
oscillator based on a four-wave interaction with feedback in an extended
nonlinear mirror,” Sov. J. Quantum Electron., vol. 24, no. 3, pp. 219–222,
1994.
Yuri A. Zakharenkov was born in Moscow, Russia,
on April 9, 1948. He received the M.Sc. degree in
physics from Moscow State University, Moscow, in
1972, and the Ph.D. degree in quantum radiophysics
from Lebedev Physical Institute, Moscow, in 1978.
During 1972–1991, he was a Senior Research As-
sociate and a Group Leader at the Lebedev Physi-
cal Institute, Moscow. During 1991–1992, he investi-
gated laser-produced plasma at Laser Facility Vulcan,
Rutherford Appleton Laboratory, Oxford, U.K. From
1993 to 1999, he was an Associate Researcher at
Short Pulse Laser Facility, Lawrence Livermore National Laboratory, Univer-
sity of California, where he was engaged in laser beam characterization. He has
designed and assembled focusing optics and plasma diagnostics for 100-TW
laser and investigated laser beam propagation through powerful high-aperture
laser amplifier. During 1999–2002, he was a Team Leader in telecom indus-
try, developing novel high-speed all-optical transceiver module for fiber optical
communication network. He joined Raytheon Space and Airborne Systems, El
Segundo, CA, as a Senior Principal Physics Engineer in November 2002 to take
part in high-power laser programs. He is the holder of two U.S. patents. He has
Authored/Coauthored two monographs on laser-produced plasma diagnostics,
65 publications in the field of lasers and nonlinear optics, and over 30 reports
in published conference proceedings.
Dr. Zakharenkov is a member of the Optical Society of America
Todd O. Clatterbuck was born in Columbus, OH,
in 1973. He received the B.A. degree in physics from
Wittenberg University, Springfield, OH, in 1996, and
the Ph.D. degree in atomic physics from the State Uni-
versity of New York (SUNY), Stony Brook, in 2003.
He is currently with the Raytheon Space and Air-
borne Systems, El Segundo, CA, where he performs
advanced development work in diode-pumped solid-
state laser systems. He has developed a number of
continuous-wave kilowatt-class laser systems based
mostly on diode-pumped Yb:YAG. His current re-
search interests include defense applications of diode-pumped ultrashort laser
systems. He has Authored/Coauthored numerous papers published in journal
and conference proceedings.
Vladimir V. Shkunov was born in Moscow, Russia,
on July 11, 1953. He received the M.S. and Ph.D.
degrees in physics from Moscow Institute of Physics
and Technology, Dolgoprudny, Russia, in 1977 and
1979, respectively.
During 1979–1997, he was a Junior Research As-
sociate, and then a Team Leader in the Institute for
Problems in Mechanics, Russian Academy of Sci-
ences, Moscow, studying basic aspects of nonlin-
ear optical phase conjugation, speckles, and dynamic
holographic gratings. During 1997–2000, he worked
on photorefractive optics and RF photonics as a Visiting Fellow, and then as
a Research Associate at JILA, University of Colorado, Boulder. From 2000 to
2003, he was a Senior Physicist in Trans Photonics, Chicago, IL, where he con-
tributed to developing direct writing techniques for polymer-based integrated
optics. In 2003, he joined the High-Energy Laser Team, Raytheon Space and
Airborne Systems, El Segundo, CA, as a Senior Principal Physics Engineer. He
has coauthored three monographs on phase conjugation and laser speckles, and
has published over 120 papers in the field of nonlinear optics and lasers.
Dr. Shkunov is a member of the Optical Society of America.

Citations
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Journal ArticleDOI
TL;DR: This phase-conjugated laser amplifier system consisting of two thermally-edge-controlled zigzag slab amplifiers and a stimulated Brillouin scattering mirror produces an average power of 213 W at 10 Hz with an optical-to-optical conversion efficiency of 11.7% and a near-diffraction-limited beam.
Abstract: We report a high-average-power and high-pulse-energy diode-pumped Nd:glass laser amplifier system consisting of two thermally-edge-controlled zigzag slab amplifiers and a stimulated Brillouin scattering mirror. This phase-conjugated system produces an average power of 213 W at 10 Hz in a 8.9 ns pulse (2.4 GW peak power) with an optical-to-optical conversion efficiency of 11.7% and a near-diffraction-limited beam. To the best of our knowledge, this is the highest performance from a Nd:glass-based laser amplifier system ever built.

94 citations


Book
05 Jan 2011
Abstract: Part 1: Gas, Chemical, and Free-Electron Lasers 1. Carbon Dioxide Lasers 2. Excimer Lasers 3. Chemical Lasers 4. High-Power Free-Electron Lasers Part 2: Diode Lasers 5. Diode Lasers 6. High-Power Diode Laser Arrays Part 3: Solid-State Lasers 7. Introduction to High-Power Solid-State Lasers 8. Zigzag Slab Lasers 9. Nd:YAG Ceramic ThinZag High-Power Laser 10. Thin-Disc Lasers 11. Heat-Capacity Lasers 12. Ultrafast Solid-State Lasers 13. Ultrafast Lasers in Thin-Disk Geometry 14. The National Ignition Facility Laser Part 4: Fiber Lasers 15. Introduction to Optical Fiber Lasers 16. Pulsed Fiber Lasers 17. High-Power Ultrafast Fiber Laser Systems 18. High-Power Fiber Lasers for Industry and Defense Part 5: Beam Combining 19. Beam Combining Index

80 citations


Book ChapterDOI
01 Jan 2008
Abstract: This chapter presents a study on stimulated light scattering resulting from induced density variations of a material system. The chapter discusses the basic concepts associated with stimulated Brillouin and stimulated Rayleigh scattering. A light-scattering process is said to be stimulated if the fluctuations are induced by the presence of the light field. Stimulated light scattering is typically more efficient than spontaneous light scattering. The chapter demonstrates that when the intensity of the incident light is sufficiently large, essentially 100% of a beam of light can be scattered in a 1-cm path as the result of stimulated scattering processes. The chapter presents a theoretical model that can treat both stimulated Brillouin and stimulated Rayleigh scattering. These two effects can conveniently be treated together because they both entail the scattering of light from inhomogeneities in thermodynamic quantities. The chapter explains electrostriction process as the tendency of materials to become compressed in the presence of an electric field. Electrostriction is of interest both as a mechanism leading to a third-order nonlinear optical response and as a coupling mechanism that leads to stimulated Brillouin scattering.

16 citations


Journal ArticleDOI
TL;DR: A numerical simulation of the amplifier implied values for the laser transition saturation intensity, the small-signal intensity gain coefficient and the gain bandwidth of 10.0 kW cm(-2), 1.6 cm(-1), and 3.7 nm respectively, and identified gain-narrowing as the dominant pulse-shaping mechanism.
Abstract: We report the demonstration of a high-power single-side-pumped Yb:YAG planar waveguide amplifier seeded by an Yb:KYW femtosecond laser. Five passes through the amplifier yielded 700-fs pulses with average powers of 50 W at 1030 nm. A numerical simulation of the amplifier implied values for the laser transition saturation intensity, the small-signal intensity gain coefficient and the gain bandwidth of 10.0 kW cm−2, 1.6 cm−1, and 3.7 nm respectively, and identified gain-narrowing as the dominant pulse-shaping mechanism.

12 citations


Journal ArticleDOI
TL;DR: The adaptive beam pointing concept has been revisited for the purpose of controlled transmission of laser energy from an optical transmitter to a target and results show that a reflectivity of R(A-PCM)>1000 could be obtained by improving the self-pumped PCM's efficiency.
Abstract: The adaptive beam pointing concept has been revisited for the purpose of controlled transmission of laser energy from an optical transmitter to a target. After illumination, a bidirectional link is established by a retro-reflector on the target and an amplifier-phase conjugate mirror (A-PCM) on the transmitter. By setting the retro-reflector’s aperture smaller than the diffraction limited spot size but big enough to provide sufficient amount of optical feedback, a stable link can be maintained and light that hits the retro-reflector’s surrounded area can simultaneously be reconverted into usable electric energy. The phase conjugate feedback ensures that amplifier’s distortions are compensated and the target tracked accurately. After deriving basic arithmetic expressions for the proposed system, a section is devoted for the motivation of free-space laser power transmission which is supposed to find varied applicability in space. As an example, power transmission from a satellite to the earth is described where recently proposed solar power generating structures on high-altitudes receive the power above the clouds to provide constant energy supply. In the experimental part, an A-PCM setup with reflectivity of about RA-PCM = 100 was realized using a semiconductor optical amplifier and a photorefractive self-pumped PCM. Simulation results show that a reflectivity of RA-PCM>1000 could be obtained by improving the self-pumped PCM’s efficiency. That would lead to a transmission efficiency of η>90%.

9 citations


References
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Book
06 May 1985
Abstract: 1. Introduction to Optical Phase Conjugation.- 2. Physics of Stimulated Scattering.- 3. Properties of Speckle-Inhomogeneous Fields.- 4. OPC by Backward Stimulated Scattering.- 5. Specific Features of OPC-SS.- 6. OPC in Four-Wave Mixing.- 7. Nonlinear Mechanisms for FWM.- 8. Other Methods of OPC.- References.

483 citations


Journal ArticleDOI
Abstract: Phase conjugation by stimulated Brillouin scattering represents a fundamentally promising approach for achieving power scaling of solid-state lasers. Following a summary of the power scaling problem and an overview of phase conjugation concepts, a review is presented of the application of phase conjugation to solid-state lasers. The author describes power scaling using demonstrated techniques for compensating static and thermally induced aberrations and depolarizations, as well as energy scaling by coherent coupling of multiple-gain media. Applications to diode-pumped lasers are discussed, as is a novel approach for power scaling of diode lasers themselves. Future research directions are indicated regarding conjugation fidelity at increasingly higher energies or with short-pulse and/or broadband lasers. >

181 citations


Journal ArticleDOI
TL;DR: A scalable architecture for a high-power, high-brightness, solid-state laser based on coherent combinations of master oscillator power amplifier chains and Adaptive optics correct the wavefront of each amplified beamlet.
Abstract: We demonstrate a scalable architecture for a high-power, high-brightness, solid-state laser based on coherent combinations of master oscillator power amplifier chains. A common master oscillator injects a sequence of multikilowatt Nd:YAG zigzag slab amplifiers. Adaptive optics correct the wavefront of each amplified beamlet. The beamlets are tiled side by side and actively phase locked to form a single output beam. The laser produces 19 kW with beam quality <2x diffraction limited. To the best of our knowledge, this is the brightest cw solid-state laser demonstrated to date.

173 citations


"2-kW Average Power CW Phase-Conjuga..." refers background in this paper

  • ...Finally, the “heat capacity laser” [8] reached record power of 31.3 kW, but only for 1–2 s of continuous operation, while operation for much longer times [ 9 ] was reported at 19 kW....

    [...]


Journal ArticleDOI
Abstract: We describe a diode-pumped Yb:YAG laser that produces 1080 W of power cw with 275% optical optical efficiency and 532 W Q-switched with M2=22 and 17% optical–optical efficiency The laser uses two composite Yb:YAG rods separated by a 90° quartz rotator for bifocusing compensation A microlensed diode array end pumps each rod, using a hollow lens duct for pump delivery By changing resonator parameters we can adjust the fundamental mode size and the output beam quality Using a flattened Gaussian intensity profile to calculate the mode-fill efficiency and clipping losses, we compare experimental data with modeled output power versus beam quality

134 citations


"2-kW Average Power CW Phase-Conjuga..." refers background in this paper

  • ...Two-rod [ 6 ] and slab [7] lasers operating at greater than 400 W have also been described....

    [...]


Journal ArticleDOI
TL;DR: A diode-pumped Yb:YAG laser with a novel end-pumping zigzag slab architecture has been developed that provides uniform transverse pump profiles, conduction cooling of the laser crystal, mechanical robustness, and ready scalability to higher powers.
Abstract: A diode-pumped Yb:YAG laser with a novel end-pumped zigzag slab architecture has been developed. This architecture provides uniform transverse pump profiles, conduction cooling of the laser crystal, mechanical robustness, and ready scalability to higher powers. At room temperature the laser emits 415 W of cw power with 30% optical conversion efficiency. An image-inverting stable resonator permits a high-brightness output of 252 W with linear polarization and an average M2 beam quality of 1.45. Q-switched pulse energies of as much as 20 mJ and average Q-switched powers of as much as 150 W were obtained while M2 was maintained at <1.5.

93 citations


"2-kW Average Power CW Phase-Conjuga..." refers background in this paper

  • ...Two-rod [6] and slab [ 7 ] lasers operating at greater than 400 W have also been described....

    [...]


Frequently Asked Questions (1)
Q1. What have the authors contributed in "2-kw average power cw phase-conjugate solid-state laser" ?

The authors have demonstrated stable operation of a 2-kW Yb: YAG phase-conjugate master oscillator power amplifier ( PCMOPA ) laser system with a loop phase-conjugate mirror ( LPCM ).