Si può desiderare di provare un trattamento naturale disfunzione erettile come un diverso per i problemi di costruzione. Al giorno d oggi ci sono diverse terapie sul mercato, ma un trattamento naturale disfunzione erettile è stato confermato qualche ora e ora di nuovo per dare risultati efficienti e permanenti. Cos è la disfunzione sessuale? L incapacità di sviluppare o sostenere una costruzione abbastanza lungo per fare l amore è chiamato disfunzione erettile, ED https://farmacia-senzaricetta.it/ o (maschio) problemi di erezione. Tutti gli uomini possono avere problemi di costruzione di volta in volta e gli scienziati considerano ED essere presenti se si verificano problemi di costruzione almeno il 25% del tempo. Alcuni fatti duri: ED Può essere dovuto a problemi emotivi. Stress, pressione, giltiness, depressione, bassa autostima e ansia prestazioni può essere la causa dei vostri problemi di costruzione. La ricerca ha confermato che il 90 per cento della disfunzione erettile è fisica in origine, non emotiva. L impotenza colpisce la maggior parte degli uomini durante la loro vita e può essere dovuto a troppo colesterolo, problemi cardiaci, diabete, ipertensione, fumo o alcol. Alcuni rimedi possono essere la ragione. Le questioni legate al movimento sono collegate. Se ti occupi dei tuoi problemi di movimento, hai piu possibilita di risolvere questo problema. Qui ci sono 5 consigli facili su come aumentare la circolazione: 1. Mangia i pasti giusti. Questo ti rendera il flusso sanguigno ovvio. Una grande parte di rimanere sani e anche mantenere il flusso sanguigno ovvio è legato al vostro piano di alimentazione quotidiana e quello che si mangia. Una buona cura per la disfunzione erettile è mangiare un piano a basso contenuto di grassi e grande alimentazione di fibre. Mangiare fibre tutti i giorni e questo viene scoperto in prodotti cerealicoli cereali integrali, frutta e verdura. Evitare il più possibile pasti pronti o pasti non sani. 2. Wonder herbal rimedi. Molti rimedi vegetali per ED eseguire bene come possono migliorare il movimento. Hanno molto meno reazioni avverse rispetto ai farmaci convenzionali e si svolgono in modo efficiente per migliorare hardons e la forza, troppo. Erbe naturali come Ginkgo Biloba sono utilizzati come una strategia per ED. Gli specialisti di erboristeria credono anche che le spezie o le erbe come noce moscata, portano al movimento intorno al corpo, tra cui il pene. 3. Vitamine naturali vitali. Gli scienziati sanitari hanno scoperto che una mancanza di supplemento è tipico tra gli uomini con ED in particolare vitamina A. Se si ha una mancanza del nutriente ossido di zinco, Questo è stato confermato per portare alla disfunzione erettile. Queste inadeguatezze derivano dal fatto che molti valori nutrizionali in quello che mangiamo piano non sono sufficienti. Aggiungere al vostro fabbisogno di nutrienti aumenterà la circolazione del sistema e migliorare questa condizione. Gli integratori alimentari sono completamente naturali, quindi non dovrete preoccuparvi dei rischi di reazioni avverse. Inoltre, queste vitamine naturali sono utili per il vostro benessere over-all. Oltre a questi vantaggi benessere, disfunzione erettile vitamine naturali e integratori costano molto meno di farmaci rimedi. 4. Esercitare. Fai una mossa e non un tablet vibrante. Camminare farà di più per migliorare e sostenere hardons di qualsiasi altra compressa chimica nel lungo periodo. Il fitness fisico manterrà bassi livelli di pressione e mantenere grandi stadi di movimento. Andando per un 20-30 minuti di movimento rapido ogni giorno, può affrontare questo problema e può sostenere la vostra libido senza l uso di qualsiasi farmaco. 5. Sottolineare. Questo è il peggior attaccante per problemi di erezione. Scopri diversi metodi per riposare. Alcuni metodi tipici per riposare includono la lettura di un libro, la meditazione, un bagno rilassante o allenamenti di respirazione. Sto solo imparando alcuni semplici allenamenti di respirazione che possono migliorare significativamente il movimento nel reparto pantaloni. Una naturale disfunzione erettile soluzioni di trattamento stanno diventando sempre più popolare con gli uomini. Questi rimedi a base di erbe sono preferiti perché non hanno reazioni avverse e sono confermati essere efficiente come il farmaco. La maggior parte degli uomini combattere parlano dei loro problemi, in particolare la disfunzione erettile come c è poca discussione sui problemi di erezione. La verita e che ED ha un impatto su piu di dieci milioni di uomini solo negli Stati Uniti. Non siete soli e l aiuto è disponibile.
Pii: s0925-3467(02)00003-4
Y. Kalisky a,*, C. Labbe a, K. Waichman a,b, L. Kravchik a, U. Rachum a,
a ‘‘Arava’’ Laser Laboratory, Rotem Industrial Park, D.N. Arava, Mishor Yamin 86800, Israel
b Laser Department, NuclearResearch Centre Negev, P.O. Box 9001, Beer Sheva 89140, Israel
c Crystal Laboratory, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences,
Received 29 June 2001; received in revised form 15 October 2001; accepted 26 November 2001
We investigate the repetitive modulation in the kHz frequency domain of a passively Q-switched, diode-pumped
Yb:YAG laser, by Cr4þ:YAG, Cr4þ:LuAG, and Cr4þ:GSGG saturable absorbers. The results presented here are fo-cused towards the design of a passively Q-switched Yb:YAG microlaser. The free-running performance of both rod anda diskYb:YAG is characterized and experimental parameters such as gain and loss are evaluated. These values, to-gether with the value of the stimulated emission cross-section, e.g. rem ¼ 3:3 Â 10À20 cm2 were found to fit between ourexperimental results and an existing numerical model which relates the experimental and physical parameters to theminimal threshold pumping power. Q-switched pulses with maximum peakpower of %10.4 kW, with energy of %0.5mJ/pulse, were extracted with 30% extraction efficiency. Ó 2002 Elsevier Science B.V. All rights reserved.
Keywords: Diode pumped lasers; Passive Q-switching; Yb:YAG laser
and microsurgery. Most commonly, systems pres-ently used are based on Nd:YAG or Nd:YVO4
Passively Q-switched, diode pumped solid state
lasers, passively Q-switched by Cr4þ:YAG, where
lasers are currently being used as miniature or
the unique characteristics of Cr4þ garnets as sat-
microlasers capable of delivering high peakoutput
power at high repetition rates and short nanosec-
Similarly to the Nd3þ/Cr4þ:YAG system, it is
ond (ns) temporal pulsewidth. These lasers are of
anticipated that the Yb3þ/Cr4þ laser system will
great interest due to their potential applications in
posses significant advantages related to micro-
micromachining, remote sensing, target ranging,
lasers and their applications. During the last severalyears there are convincing indications pertain-ing the Yb3þ-based diode-pumped lasers and their
possibility to replace the currently used Nd3þ-
Corresponding author. Tel.: +972-7-655-6301; fax: +972-7-
based systems, in particular the diode-pumped
E-mail address: [email protected] (Y. Kalisky).
0925-3467/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 3 4 6 7 ( 0 2 ) 0 0 0 0 3 - 4
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
Solid state lasers based on Yb3þ doped solid
nonradiative processes among excited states,
hosts emit coherent radiation peaking at 1030 nm
or quenching of excited state luminescence.
=2ðA1Þ ! 2F7=2ðZ3Þ, levels, where A1 and Z3
Pumping wavelengths of 940 or 970 nm––utiliza-
are the J-Starkcomponents located at 10,327 and
tion of the reliable Al-free InGaAs diode lasers
612 cmÀ1, respectively [2]. Yb-based solid-state
• Yb is capable of energy storage due to its long
lasers have several advantages over Nd-doped la-
lifetime––in the 0.95–1.2 ms temporal domain,
sers. The advantages of Yb laser can be summa-
• Finally, there is significant advantage in using
the YAG as laser host since both Yb and Nd
• Low quantum defect e.g. 91% quantum effi-
ciency, hence low fractional heating (<11% as
chanical properties of the hosting YAG.
compared to 37–43% in Nd3þ:YAG) [3], andsmaller thermal load on the crystal.
The main physical and optical characteristics of
• Broad absorption bandwidth of about 10 nm
Yb3þ:YAG are summarized in Table 1.
and 940 nm ð2F7=2 ! 2F5=2Þ, that implies more
The main disadvantage of Yb doped host is its
flexibility on the pumping diode wavelength
quasi-three-level nature due to the thermal popu-
control within the absorption band of the gain
lation of the highest J splitting of the 4F7=2 lower
medium, and on the diode temperature. (This
terminating lasing level, which is about 612 cmÀ1
absorption bandwidth is five times broader than
above the ground level. This thermal population
the 808-nm absorption transition in Nd:YAG.)
has deleterious effects of resonant re-absorption of
• Broad emission bandwidth which results in
the laser emission from the ground terminal Stark
tunability and the ability to generate short
state, which is thermally populated at 300 K by
about 5% of the 4F7=2 population. Therefore, it is
• High doping levels––up to 20 at.% and even
difficult to obtain population inversion at room
higher levels, without concentration quenching
temperature, and therefore, the lasing threshold is
high and its efficiency is consequently low. Efficient
• Due to the simple 4f13 electronic configuration
population inversion is achieved by either pump-
of Yb3þ ion, there are no relevant higher lying
ing at high pump power densities at 300 K (1.5–10
excited states, and therefore, there is no excited
kW/cm2) [4], or by depopulation of the highest
state absorption, upconversion phenomena,
Starkcomponents. The latter option is achieved by
Table 1Main physical characteristics of Yb:YAG crystal
Change of refraction index with temperature
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
cooling down the system to low temperatures,
used to study the repetitive modulation and
where only the lowest Starklevels are thermally
passively Q-switching of Yb laser. The Yb:YAG
laser rod, (sample #1) supplied by VLOC (FL,
For several applications, mainly industrial, Q-
USA), was / ¼ 2 mm in diameter and l ¼ 4 mm
switched nanosecond pulses are the preferred
in length, and was doped with 10 at.% of Yb3þ.
choice over the high peakpower, sub picosec-
ond mode-locked Yb:YAG laser system [5]. It is
sample #2 (/ ¼ 28 mm, thickness of 1.95 mm),
therefore necessary to optimize the conditions,
was supplied by Gospel. The Yb3þ concentration
which allow the passively Q-switched operation of
in the diskwas calculated from the absorption
Yb:YAG laser towards applications that require
spectra to be 8.5 at.%. Both laser crystals had
mid-levels of average power or alternatively, me-
flat/flat surfaces, where the laser rod was HT/HR
dium peakpower level at 300 K, utilizing a com-
@ 940/1030 nm, respectively, on the pump side
and AR @1030 nm on the other side, and the
The ytterbium laser is currently regarded as a
diskhad an AR/AR coating @ 1030 nm on both
suitable candidate to generate pulses having rela-
tively high peakpower, due to the long lifetime of
the excited level 2F5=2 of Yb3þ ion. This charac-
Yb:YAG samples used are presented in Table 2.
teristics, coupled with the ability to obtain high
The pumping transition peakat 940 nm is utilized
Yb3þ doping levels (up to 20 at.% without con-
for diode pumping using InGaAs diode arrays,
centration quenching), make the ytterbium doped
which are more robust than the AlGaAs diodes
solids an ideal candidate as a microlaser in the
1030–1050 nm spectral range. This laser is pas-
sively Q-switched by saturable absorbers such as
pumped by two types of conductively cooled fiber
Cr4þ:YAG and other quadrivalent chromium
coupled diode array lasers. The first one, an OPC-
doped garnets, yielding repetitive modulation and
B030-940-FC, with a nominal maximum fiber dia-
meter of 1.55 mm, NA of 0.22 and an output
In the present paper, we investigate the optimal
power of 30 W, and a second diode model OPC-
parameters of an efficient operation of a micro-
D060-940-FC, 1.5 mm, 0.1 NA, with a nominal
laser based on a passively Q-switched diode-pumped
output power of 60 W. The diode laser emission
Yb:YAG laser, using several Cr4þ-doped garnets
was centered at 940 nm at normal operating tem-
perature of 20 °C with an emission spectralbandwidth (full width at half maximum, FWHM)of less than 4 nm. The temperature and hence the
wavelength of the pumping diode were regulatedby a chiller (Neslab-CFT-33). The pump radiation
The laser experimental set-up is presented
was collimated and focused on the front surface of
in Fig. 1. Two types of Yb:YAG crystals were
the crystal with a focusing lens (OPC-ORU-03) to
Fig. 1. Schematic of the passively Q-switched diode pumped Yb:YAG laser set-up.
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
Table 2Experimental parameters of Yb:YAG crystals used in this paper
pumped at 300 K, and which affects the laser
crystalline rod was inserted inside a water-cooled
For the CW operating mode, we used an Ophir
controlled by a thermoelectric re-circulating solid-
power meter, (Ophir 30A-SH) to monitor the
state chiller (Melcor MLA 270). In order to obtain
a good thermal contact between the crystal and the
For the pulsed passively Q-switched operation,
heat sink, the Yb:YAG crystal was wrapped by a
we have inserted inside the cavity, perpendicular
thin (0.1 mm) indium foil and then attached to the
to the optical axis one of the crystalline samples
either Cr4þ:YAG, Cr4þ:LuAG (Lu3Al5O12), or
In the case of the Yb-crystal disk, it was sand-
Cr4þ:GSGG, all with nominal concentration of the
wiched between a water-cooled, ring-shaped, cir-
chromium ion in the range 0.15–0.3 at.%. The
cular heat sinkand a copper ring (5 mm aperture).
Cr4þ:YAG, Cr4þ:LuAG samples were kindly sup-
The copper ring pressed the diskagainst an indium
plied by Dr. M. Kokta of Bicron Crystals Products
foil, to achieve a good thermal contact of the
(USA), and that of Cr4þ:GSGG by Dr. Igor Iva-
crystal disksurface to the copper heat sinkunit.
nov, of the Research of Material Science and
We assume that the heat sinkand the crystal sur-
Technology (Russia). Some important experi-
face are always in thermal equilibrium.
mental parameters [1,6] of the Cr4þ doped satu-
The laser resonator consisted of an output
rable absorbers used in these experiments are
presented in Table 3. The Q-switch crystal surfaces
ROC ¼ 150 mm, with various reflectivities ranging
were polished, without coating, and therefore their
from R ¼ 85% to 98% @ 1030–1060 nm. A front
transmission spectra are accounted for Fresnel
flat mirror, with high transmission coating at 940
nm and high-reflectivity (HR) coating at 1030 nm,
The Q-switched output laser signal was detected
was utilized with the diskcrystal. The length of the
by a fast silicon photodiode (risetime <1 ns, col-
diskand rod laser cavities, was lc ¼ 52 mm, which
lected by a digital oscilloscope (Tektronix TDS
yielded thermally undistorted waist xc % 150 lm,
724A), and further analyzed by commercial data
where xc is the radius (1=e2) of the fundamental
processing software. For laser pulse frequency
mode size on the backmirror. This length ac-
measurements, a detector with a slower risetime
counts for the thermal lensing which results from
(3.5–18 ls) was employed, followed by an FFT
the high pumping power densities when the laser is
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
Table 3Physical and optical parameters of Cr4þ:YAG samples used as saturable absorbers in diode-pumped Yb:YAG laser
The thickness of the sample is l, a is the absorption coefficient, and T0 is the small signal transmission.
and 15.7 at.%. The saturable absorbers used inthese cases was sample (a) (e.g. la ¼ 0:85 mm). The
3.1. Passively Q-switched operation––results and
average output power for the 10 and 12 at.% was
in the hundreds of mW, in the pumping rangeof 26–37 W. The pulsewidths (FWHM) in this
pumping power regime were 46 and 34 ns and
3.1.1.1. Medium pump power level (up to 30 W).
the modulation frequency of 4.6 and 5.65 kHz,
We passively Q-switched several Yb:YAG laser
respectively. We did not test the diskwith CYb ¼
disks with two uncooled, polished Cr4þ:YAG sam-
15:7 at.% for passive Q-switching due to poor
ples denoted by (a) and (b). See Table 3 for details.
free running laser performance especially above
In these experiments an output coupling mirror
Pin ¼ 40 W. This will be discussed further in Sec-
with a reflectivity of R ¼ 95% was used. Also, in
the first set of Q-switching experiments we limitedthe input pumping power (pin) to levels of up to
3.1.1.2. High pump power level (up to 60 W). We
tested both Yb:YAG rod (as will be described in
The Q-switched Yb:YAG (8.5 at.%) laser per-
the following section) and Yb:YAG diskfor Q-
formance produced about 650 mW average output
switching under higher pumping load. For that
power at 30 W input pumping power. At this
purpose we used a fiber coupled diode array of 60
pumping level, the Q-switching element surface
W output power at 940 nm. The optimal output
was damaged and the laser performance degraded
coupling of the laser resonator was R ¼ 85%, and
by 50%. The pulsewidth, s (denoted by the
the Cr4þ:YAG was sample (a). The performance of
FWHM), was of the value s % 30 ns both at low
both Yb:YAG rod and diskwas degraded due to
and maximum input pumping power, for samples
damage at the Cr4þ:YAG surface. When the pas-
(a) and (b) of the saturable absorbers.
sively Q-switched Yb:YAG disk(28 Â 1:95 mm)
For Yb:YAG disklaser with the saturable ab-
was pumped in the range of 20–51 W, it produced
sorber sample (a), the modulation frequency of the
an average output power of 3 W at 31 W pumping
1030–1048 nm laser emission varied from f % 4 to
power. At that point the performance was de-
12 kHz at input pumping levels of Pin ¼ 21 and
graded and the system was realigned, which re-
Pin ¼ 31 W, respectively. Although there are slight
sulted-in 4.2 W average output power @ 51 W
differences between the two samples of the satu-
rable absorbers, we cannot draw any comparative
In a separate experiment at Pin ¼ 51:8 W, using
conclusions pertaining their quality as passive Q-
saturable absorber samples (a) and (b) we obtained
switches, since the Cr4þ samples were not fabri-
pulses of temporal widths of 43.4 and 54.4 ns
(FWHM), respectively, and modulation frequency
Q-switching operation was applied to Yb-disk
of 9.6 and 16 kHz, respectively. All these mea-
geometry with Yb3þ concentrations: CYb ¼ 10, 12,
surements were carried out using output coupling
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
reflectivity of R ¼ 95% and keeping the laser
of Pin ¼ 28 W we observed damage to the saturable
absorber and degradation in the performance by%25%. The maximum average output power after
3.1.2. Laser rod configuration (sample #1)
realignment was Pout ¼ 4:2 W @ Pin ¼ 43:5 W
3.1.2.1. Low pump power level (up to 30 W). Op-
input power and the curve was slightly saturated.
erating passively Q-switched Yb:YAG laser rod
In the pumping range of 20–51 W, the pulsewidths
for both Cr4þ samples (a) and (b) at 30 W pumping
ranged from 48 to 38 ns, respectively, and the laser
power, produced pulses having temporal pulse-
pulse frequency varied from 2 to 23.4 kHz, re-
width (FWHM) of s % 16 ns, at an average mod-
ulation frequency of f % 4 kHz. The average
To improve the Q-switching performance, we
output power of Yb:YAG laser rod was lower
placed the Cr4þ:YAG inside a water cooled heat
than the diskgeometry, namely Pout % 100 mW,
sinkat 15 °C. In this configuration (R ¼ 85%), the
due to damage to the Q-switching surface. Signif-
maximum average output power was Pout ¼ 4:5 W
icant improvement in the Q-switched laser per-
at an input pumping power of Pin ¼ 32:5 W. Fur-
formance was obtained using an output coupler
ther increase in the pumping power, up to 53 W,
with a reflectivity of R ¼ 85%. We obtained max-
led to saturation with maximum average output
imum average output power of 1.32 W, with a
power, namely, Pout % 4:8 W. Under the same
slope efficiency of g ¼ 12:8%. For the 1.32 W
experimental conditions, the free-running output
average output power (@ 31 W input pumping
power was %16 W, therefore the extraction effi-
power), the modulation frequency was f % 13
kHz, with an average pulsewidth of 22 ns. This
switched pulsewidth and the modulation frequency
implies that the pulse energy is %100 lJ/pulse and
on the input pumping power is presented in Fig. 2.
the peakpower is %4.5 kW. At present the results
From this figure we observe that in the pumping
with R ¼ 85% are preliminary and no attempt was
range of 16–33 W, the repetition rate changed
made to optimize the Q-switched performance
significantly from 1.2 to 9.2 kHz, respectively. The
with other output couplers. All the Q-switched
change in the pulsewidth in this range was from
measurements were performed with Cr4þ:YAG
54.3 to 48 ns, respectively. This configuration
sample (a). The maximum error in the pulsewidth
yields pulse energy of 0.5 mJ/pulse and peakpower
measurements is in the range of Æ10%. The free
running average output power was Pout ¼ 5:3 Wunder
pumping power and output coupling reflectivity,(31 W, Theat sink ¼ Tcrystal ¼ 15 °C, and R ¼ 85%,respectively). The fraction of the Q-switchedpower relative to the free-running output power isdefined by g
experimental conditions. We should note here thatdue to the surface damage on the Q-switching el-ement and consequently, the output power de-gradation at about Pin % 26–30 W, the pumpingpower did not exceed this value.
3.1.2.2. High pump power level (up to 60 W). Wealso tested for Q-switching the laser rod (2 Â 4mm) using Cr4þ:YAG sample (a) under higher
Fig. 2. The repetition frequency and output pulsewidths versus
pumping load similarly to what have been per-
pumping power of a passively Q-switched, diode-pumped
formed with Yb:YAG disk. The output coupler
Yb:YAG/Cr4þ:YAG. The output coupling reflectivity is
used was also R ¼ 85%. At input pumping power
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
Finally, we used the relatively high peak
Cr4þ:YAG when operated as saturable absorbers
power to obtain frequency doubling at 525 nm by
for Yb:YAG laser. With Cr4þ:LuAG (l ¼ 1:43
using KTP or BBO nonlinear crystals. Both crys-
mm), we obtained an average output power of
tals generated a modulated green light with a
Pout % 235 mW, at Pin % 46 W. The modulation
repetition rate in the kHz frequency regime, with
frequency in the pumping range 30–46 W changed
pulsewidths of about 20–40 ns (FWHM). At pre-
from f % 0:6 to 1.7 kHz, respectively. The pulse-
sent, the output power of the green laser emission
width (FWHM) exhibited a small change namely,
is low due to the optical system, which is not op-
s % 26:2 to 24.7 ns, which is within the experi-
mental error. For the Cr4þ:GSGG (l ¼ 0:2 mm),we obtained average output power of Pout % 220
3.2. Passive Q-switching with Cr4þ:LuAG and
mW, with f % 2:7 k Hz and s % 16 ns at Pin % 60 W.
We have conducted preliminary experiments
with two additional saturable absorbers based on
In order to characterize the working parameters
Cr4þ-doped garnets. For these preliminary testing
and optimal conditions for passively Q-switched
we used Yb:YAG disk(sample #1) with Yb3þ
ytterbium laser, free-running operation mode has
doping of 8.5 and 10 at.% The optimal output
been studied extensively, as well. The free-running
couplers used in all the experiments were of
mode was operated first, in order to characterize
Rout ¼ 99% and 85% for both Cr4þ:LuAG and
the working parameters and optimal conditions
Cr4þ:GSGG, respectively. The Cr4þ:LuAG and
for an efficient passive Q-switching operation of
Cr4þ:GSGG were polished, uncoated, with small
Yb:YAG laser (using samples #1 and #2), in two
signal transmission of T0 % 66% and 85%, respec-
different geometries and at several heat sinktem-
tively. The Cr4þ:LuAG is of special interest due to
peratures, ranging from 5 to 20 °C. The diode-
its highest ratio of rgsa=resa values relative to other
pumped Yb:YAG laser performance for Yb:YAG
garnets, where rgsa and resa are the ground state
rod and diskat 15 °C is presented in Fig. 3(a).
and the excited state absorption cross-sections,
Since the experimental results at different temper-
atures behave similarly, we present only the per-
formance at 15 °C. The Yb concentration in the
much lower average output power relative to
rod used is CYb ¼ 10 at.% (/ ¼ 2 mm, l ¼ 4 mm)
Fig. 3. (a) Laser output power of a free-running CW Yb:YAG laser rod (CYb ¼ 10 at.%) and disk(CYb ¼ 8:5 at.%) versus incidentpumping power at 940 nm, at heat sinktemperature of 15 °C. (b) Laser output power of a free-running CW Yb:YAG laser rod(CYb ¼ 10 at.%) versus incident pumping power at 940 nm, at different heat sinktemperatures. The various slope efficiencies are in-dicated in the figure.
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
and for the disk8.5 at.%. (The cavity character-
was calculated to be T ðr ¼ r0Þ ¼ 15 °C. This per-
istics of this set-up were similar to previous ex-
formance is similar (although different in beam
periments, namely, cavity length of 52 mm, output
quality) to the results of Giesen et al. [8] for Yb(8
coupling mirror of ROC ¼ 150 mm and a reflec-
at.%):YAG, under similar pump power level, and
tivity of R ¼ 95%.) Thermal gradients result in
at ambient temperature. Under these experimental
thermal lensing and efficiency reduction due to the
conditions, Giesen et al. obtained free-running
high temperature and subsequently, an increase in
output power of about 18 W by using a thin disk
the lower Starklevel population of the terminal
laser (0.3 mm thickness) with four double-passes
lasing level. In order to minimize the thermal load
of the pump light. Furthermore, improvement in
on the crystal we reduced the radial temperature
the output power and in the total optical efficiency
gradients by employing a diskshaped geometry for
were obtained by Karszewski et al. [9] (to values of
the laser medium. In this geometry, the thermal
47–45%), in the same temperature range, however,
gradients are collinear with the laser beam and the
with eightfold passes of the pumping light through
axial heat removal is easier due the thinner di-
the crystal. Our total optical efficiencies at 54 W
mension of the disk. In the case of the disk con-
pumping input power (single-pass) obtained at
figuration, the laser output power showed linear
heat sinktemperatures of, T ¼ 5, 10, and 20 °C,
dependence on the incident input power at same
are 39%, 36.6%, and 34.7%, respectively.
heat sinktemperature range, while the laser rod
The beam quality factor, M 2, of Yb:YAG was
performance deviated from linearity.
measured in both the rod and diskgeometries. The
The slope efficiency, g , was calculated from the
values of M 2 yield further indication as to the in-
linear dependence of the output power on the
fluence of the thermal gradients on the laser per-
formance. The beam quality was measured byusing the knife-edge technique. The beam size DðzÞ
was measured between 13.5% and 86.5% clip-level
where Pout is the laser output power, Pin is the in-
[10]. The measured values of DðzÞ were fitted to the
put pumping power and Pth is the extrapolated
threshold power. The maximum output power
obtained at an operating temperature of T
Tcrystal ¼ 5 °C in the above pumping scheme is
where D0 is the width of the beam waist located at
Pout ¼ 22:2 W, with a slope efficiency of g ¼ 56%.
a position z0, and h is the divergence angle. By
When the crystal temperature was increased up
using these parameters, the values of M 2 were
to 20 °C, the Yb:YAG output power degraded
slightly to Pout ¼ 19 W, with a slope efficiency,
g ¼ 53:6%. The free-running performance of
Yb:YAG rod at different operating temperatures ispresented in Fig. 3(b). In all the experiments, the
where k is the laser wavelength. For Yb:YAG rod
laser was pumped around the maximum absorp-
(CYb ¼ 10 at.%) and Yb:YAG disk(CYb ¼ 8:5
tion peak(941 nm), where most of the pump light
at.%), the beam quality factors at 53 W input
was absorbed. The temperature effects on the laser
power are 3.15 and 2.51, respectively. This con-
performance are clearly observed at high pumping
firms our assumption of better thermal manage-
load, where deviation from linear fitting in the
input–output curves are observed. The radialtemperature gradient inside the laser rod (relative
to the heat sinktemperature) was calculated usingthe formula of Innocenzi et al. [7]. In the rod
The concentration of Yb3þ active ion is a cru-
center r ¼ 0, the relative temperature, T ðr ¼ 0Þ
cial factor in the proper performance of Yb laser.
was calculated as 140 °C, while at the crystal sur-
This stems from the quasi-three level nature of
face, namely, at r ¼ r0 ¼ 1 mm, the temperature
ytterbium laser and the reabsorption of the laser
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
emission. We tested several samples of Yb:YAG
Only the 10 at.% samples of this set performed
with different doping levels in order to establish a
similarly to Yb:YAG rod (samples #3), in the
relationship between the laser performance and
output coupling range of R ¼ 99–95%, and with
the active ion concentration. All the experiments
were performed at crystal heat sinktemperature,Theat sink % Tcrystal ¼ 16 °C. The lengths of the 5 and
10 at.% laser rods were adjusted for %87% and%95% absorption of the pumping power, respec-
The total round-trip losses in the Yb:YAG laser
tively. The laser performance tests for samples #3
system were estimated by using the Findlay–Clay
and #4 were made on samples from the same
method. This is done by measuring the various
vendor and under the same experimental condi-
pumping input power at threshold versus the out-
tions, which implies similar growth and coating
put coupling mirror reflectivities [11]. The follow-
conditions. By using set samples #3 of Yb:YAG
ing equation provides the relation between the
rods with CYb ¼ 10 and 5 at.%, we obtained
slope efficiencies of 37% and 25.5%, respectively.
The results were recorded for a variety of out-
put couplers, ranging from R ¼ 92% to 99% (at
where R is the reflectivity of the output mirror,
Tcrystal ¼ 16 °C). We also used a mechanical chop-
and K is the pumping coefficient defined as the
per (duty cycle of 50%) to minimize thermal effects
product of all the coefficients that lead to the
and possible damage to the crystals. For the laser
population of the upper lasing state. Eq. (1) is
rods with CYb ¼ 10 and 5 at.%, the laser per-
valid for only a four-level system. We use it for
formed best with output coupler of R ¼ 95%. For
Yb3þ assuming that under proper thermal man-
CYb ¼ 5 at.% we observed a variation of %20% in
agement the system is a quasi-three-level. This
the maximum output power among different
point, will be verified later in the text. The incident
samples from the same boule. Also we noticed
pumping power at threshold is defined by Pth, and
instabilities in the output power above 20 W ab-
L represents the total round-trip losses, defined as:
sorbed power, probably due to thermal effects in-
L ¼ 2dl þ LM. Here, l is the crystal length, and d
side the Yb:YAG crystal. We should note here the
are the passive losses per unit length. The value of
effect of pumping wavelength variation with the
LM represents various losses [12], such as absorp-
diode current on the Yb laser performance, for
tion or scattering losses at the back(HR) mirror,
both CYb ¼ 10 and 5 at.% While the optimal
or diffraction losses of the resonator and is esti-
wavelength at the maximum current is k ¼ 942
mated as LM % 1%. The laser was operated for
nm, there is a significant blue shift at lower diode
optimal performance using different output cou-
currents, and this affects the amount of the ab-
pler reflectivities ranging from 85% to 98%. The
sorbed power. With the CYb ¼ 10 at.% the insta-
best performance obtained for both the Yb:YAG
bilities of output power with time were much
rod and the disk(samples #1 and #2) were at
higher and in some cases led to 20% degradation of
R ¼ 95%. The values of L and K can be extracted
the initial power after 25 min of CW operation.
from the linear plot of À lnðRÞ vs. Pth according to
We should mention here that unlike other re-
Eq. (1). The values for the total round-trip losses
ports, no lasing action was observed under the
are, L ¼ 8% and the factor K ¼ 6:725 Â 10À3 WÀ1
same experimental conditions and at ambient
for 10 at.% ytterbium laser rod. For the 8.5 at.%
temperature with samples #4, namely, CYb ¼ 20
Yb3þ laser disk, the total round trip losses are,
and 30 at.% (set samples #4), either when pumped
L ¼ 9:3%, and the factor K is, K ¼ 7:15 Â 10À3
at the absorption peak(941 nm) or at the shoulder
WÀ1. The experimental measurement error is
of the absorption (935 nm). This is attributed to
Æ10%. The passive losses per unit length extracted
the strong ground state re-absorption at the lasing
from our results (assuming that LM % 1%) are
wavelength. All the samples were of diskshape
8.75% and 21% per cm for the ytterbium laser rod
and adjusted for 60–63% absorption at 941 nm.
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
The small signal gain at threshold is calculated
In the present paper, we report the results of
optimizing the working parameters of an effi-
cient operation of a microlaser, based on a passiveQ-switched diode-pumped Yb:YAG laser. The
From this expression, the small signal gain at
resonator optimization accounts for the thermal
threshold (with 95% reflectivity of the output
lensing which results from the high pumping
coupler) is obtained: gthðYb-rodÞ % 0:132 cmÀ1
power densities when the laser is pumped at 300 K,
and gthðYb-diskÞ % 0:4 cmÀ1. From the values of
and which affects the laser performance and its
gain at threshold and the known values of stimu-
lated emission cross-section, the population in-
The usefulness of tetravalent chromium-doped
version at threshold can be estimated using the
garnets as saturable absorbers is demonstrated by
achieving repetitive modulation of a CW Yb:YAGlaser operation. By using Yb:YAG/Cr4þ:YAG
crystals, it produces modulated light in the kHz
frequency range with pulsewidths in the 16–48 ns
temporal regime. Maximum peakpower of 10.4
2th ¼ N2ðj¼1Þth is the lowest Starkcompo-
is reported. The optimization yields extraction
of Q-switched pulses of %0.5 mJ/pulse, with
j ¼ 3 Starkcomponent of the ground state (2F
extraction efficiency of %30% relative to the free-
cmÀ1 above the ground state. The stimulated
conditions. Our experimental results of aver-
age output power, modulation frequency, and
pulsewidth in Yb:YAG/Cr4þ:YAG system are in
that at threshold, the ground state population
agreement with the recent results of Patel and
depletion due to ground state absorption is small,
Beach [15]. The performance of Cr4þ:YAG as a
saturable absorber is superior relative to that of
1 ( NT (N1 is the ground state ion density
Cr4þ:LuAG or Cr4þ:GSGG. By utilizing the sig-
nificant advantages of Yb3þ ion, we are currentlydeveloping a compact diode-pumped Yb:YAG
and it follows that gain at threshold is given by
This workwas supported by the ‘‘MAGNET’’
th is the population inversion at thresh-
program of the Chief Scientist Office at the Israeli
5:7 Â 1018 and 1:74 Â 1019 cmÀ3, for Yb:YAG rod
Ministry of Industry and Trade, Consortium of
and disk, respectively. The differences in gain,
Diode Pumped Solid State Lasers (LESHED).
losses, and hence, in the population inversion atthreshold are attributed the different crystal qual-ity and the presence of impurities which are pre-
sent in small amounts in the Yb:YAG samples andwhich contributes to degradation in laser perfor-
[1] Y. Kalisky, A. Ben Amar-Baranga, Y. Shimony, M.R.
Y. Kalisky et al. / Optical Materials 19 (2002) 403–413
[2] K.S. Bagdasarov, G.A. Bogomolova, D.N. Vylegzhanin,
[10] A.E. Siegman, M.W. Sansett, T.F. Johnston, IEEE J.
A.A. Kaminskii, A.M. Kevorkov, A.M. Prokhorov, Sov.
[11] D. Findlay, R.A. Clay, Phys. Lett. 20 (1966) 277.
[3] T.Y. Fan, IEEE J. Quant. Electron. 29 (1993) 1457.
[12] W. Koechner, Solid State Laser Engineering, fifth ed.,
[4] A. Giesen, H. Hugel, A. Voss, K. Wittig, U. Brauch, H.
Opower, Appl. Phys. B 58 (1994) 365.
[13] H.W. Bruesselbach, D.S. Sumida, R.A. Reeder, R.W.
[5] J. Aus der Au, G.J. Spuhler, T. Sudmeyer, R. Paschotta, R.
Byren, IEEE. J. Quant. Electron. 3 (1) (1997) 105.
Hovel, M. Moser, S. Erhard, M. Karszewski, A. Giesen, U.
[14] P. Le Boulanger, S. Levy, Z. Burshtein, Y. Kalisky, S.R.
Rotman, P. Deng, H. Yin, W. Chen, F. Gan, Spectroscopic
[6] Z. Burshtein, P. Blau, Y. Kalisky, Y. Shimony, M. Kokta,
properties of Yb3þ-doped silicate and fluorophosphate
IEEE J. Quant. Electron. 34 (1998) 292.
[7] M.E. Innocenzi, H.T. Yura, C.L. Fincher, R.A. Fields,
[15] F.D. Patel, R.J. Beach, IEEE. J. Quant. Electron. 37 (2001)
Appl. Phys. Lett. 56 (19) (1990) 1831.
[8] A. Giesen, U. Brauch, I. Johannsen, M. Karszewski, C.
[16] R.J. Beach, Opt. Commun. 123 (1995) 385.
Stewen, A. Voss, High-power near diffraction-limited and
[17] L.D. DeLoach, S.A. Payne, L.L. Chase, L.K. Smith, W.L.
single-frequency operation of Yb:YAG thin disklaser, in:
Kway, W.F. Krupke, IEEE J. Quant. Electron. 29 (1993)
S.A. Scheps, C. Pollock(Eds.), OSA Trends in Optics and
Photonics on Advanced Solid State Lasers, vol. 1, Optical
[18] V.V. Ter-Mikirtychev, V.A. Fromzel, Appl. Opt. 39 (27)
Society of America, Washington, DC, 1996, pp. 11–13.
[9] M. Karszewski, U. Brauch, K. Contag, S. Erhard, A.
[19] S.A. Payne, L.K. Smith, L.D. DeLoach, W.L. Kway, J.B.
Giesen, I. Johannsen, C. Stewen, A. Voss, 100-w TEM00
Tassano, W.F. Krupke, IEEE. J. Quant. Electron. 30
operation of Yb:YAG thin disklaser with high efficiency,
in: S.A. Scheps, C. Pollock(Eds.), OSA Trends in Optics
[20] D.C. Brown, IEEE. J. Quant. Electron. 33 (1997) 861.
and Photonics, vol. 19, Advanced Solid State Lasers,
[21] D.S. Sumida, T.Y. Fan, Opt. Lett. 19 (17) (1994) 1343.
Optical Society of America, Washington, DC, 1996,
[22] M.I. Demchuk, N.V. Kuleshov, V.P. Mikahailov, IEEE. J.
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