V:YAG saturable absorber for flash-lamp
and diode pumped solid state lasers
Jan Šulca , Helena Jelínkováa , Michal Němeca
Karel Nejezchlebb , Václav Škodaba Czech Technical University, Faculty of Nuclear Sciences and Physical EngineeringBřehová 7, 115 19 Prague 1, Czech Republicb Crytur, Ltd. Turnov, Palackého 175, 511 01 Turnov, Czech Republic

ABSTRACT
V:YAG saturable absorber was used for efficient Q-switching and mode-locking of Nd:YAG and Nd:YAP flashlamp or diode pumped lasers operating in 1.3 µm region. Crystals of Yttrium-Aluminum Garnet (YAG) dopedwith three-valence vanadium V3+ in tetrahedral position (V:YAG) were grown using of Czochralski method
in reducing protective atmosphere. High purity oxides were used for crystal growth (Y2 O3 (5N), Al2 O3 (5N),V2 O5 (4N)). Concentration of V2 O5 in the melt reached up to 1 wt. %. Discs of the diameter 5 or 10 mm and ofvarious thickness were machined from grown V:YAG crystals. The discs were both sides polished and AR coated
so that minimum reflectivity at 1.08 and 1.34 microns was reached. The initial transmission of the saturable
absorber was dependent on the sample’s thickness and its annealing process. We report stability improvementof passively mode-locked (by these V:YAG crystals) Nd:YAP flash-lamp pumped lasers. The maximum output
energy 53 mJ at wavelength 1340 nm was obtained for Nd:YAP flash-lamp pumped laser operating at repetition
rate 5 Hz. Mode-locked train envelope width was measured to be 22 ns (FWHM). Individual pulses inside thetrain were shorter than 1 ns. Also results with composite Nd:YAG rod Q-switched by V:YAG crystal and with
Nd:YAG/V:YAG monolith rod under CW longitudinal diode pumping was obtained and compared. These laser
systems represent new powerfull sources in the near infrared region.
Keywords: V:YAG saturable absorber, Nd:YAP laser, passive Q-switching, passive mode-locking, monolith
crystal1. INTRODUCTION
In the past few years, the target of many investigations has been generation of radiation with the wavelength
in the vicinity of 1.5 µm — so called “eye safe” radiation. These wavelengths can be generated using of Ramanor parametric conversion in nonlinear crystals excited by the radiation ∼ 1.3 µm.1, 2 Threshold intensity needed
for the initialization of those nonlinear effects suppose the higher power it means that the primary laser could
work in Q-switched or mode-locked regime with an active or passive Q-switch. The passive Q-switch — saturable
absorbers — has some advantages in comparison with the active one: they are compact, inexpensive and easyto-operate. In the past, they were mostly formed by dyes dissolved in various solvent. As the saturable dyes
have to fulfill the requirement that they can absorb quanta of generated laser radiation resulting in bleaching,no such dyes are available for every type of laser. On the other hand if the absorbers with proper saturable
absorption exist, mostly they have disadvantages of liquid substances — temperature and long-term instability.3
Therefore solid-state materials possessing reliable saturable absorption, good chemical and physical properties
are the object of constant interest of researchers. Many bulk passive Q-switched lasers use the Cr4+ :YAG asa saturable absorber.4, 5 The saturable absorption of Cr4+ ions in the near infrared extends from 0.8 µm up
Further author information: (Send correspondence to J.Š.)J.Š.: E-mail: sulc@troja.fjfi.cvut.cz, Tel.: +420 221 912 240, Fax: +420 221 912 252
H.J.: E-mail: hjelin@troja.fjfi.cvut.cz, Tel.: +420 221 912 243, Fax: +420 221 912 252
M.N.: E-mail: nemecm@troja.fjfi.cvut.cz, Tel.: +420 221 912 259, Fax: +420 221 912 252
K.N.: E-mail: nejezchleb@crytur.cz, Tel.: +420 481 319 511, Fax: +420 481 322 323
V.Š.: E-mail: skoda@crytur.cz, Tel.: +420 481 319 511, Fax: +420 481 322 323

to 1.2 µm, making it suitable for the 0.946 µm and 1.064 µm Nd3+ transitions. However, it is not suitable forlonger wavelength transitions, such as 1.34 µm transitions of Nd3+ ions. More recently the use of quantum wells
in semiconductor saturable absorber mirror (SESAM) has produced ultrashort pulses at longer wavelengths at
1.342 µm or 1.53 µm.6, 7 These SESAM devices however have relatively high loss, giving low pulse energies, andtheir low damage threshold limits their scalability.
As reliable Q-switch for 1.3 µm spectral region, solid state crystal V:YAG (Yttrium-Aluminum Garnet (YAG)
doped with three-valence vanadium V3+ ) has appeared.8–14 This saturable absorber was studied in many arrangements: for switching of Nd:YAP, Nd:YAG, Nd:YVO4 or Nd:KGW laser (λ ∼ 1.3 µm) with the flashlamp14, 15
or diode16–20 pumping. In flash-lamp pumped systems, the maximum energy obtained with the train of mode
locked pulses reported in those works were 4.5 mJ14 for the combination Nd:YAG/V:YAG, and 8 mJ for the combination Nd:YAP/ V:YAG. In diode pumped laser systems, the maximum reported20 average power, peak power,
and pulse energy were 2.1 W (Nd:YVO4 / V:YAG), 2.8 kW (Nd:YAP/ V:YAG) and 79 µJ (Nd:YAG/ V:YAG),
respectively.
In our previous study15 we have obtained as maximum 10 mJ and 27 mJ in 20 ns long (FWHM) train of pulses
for Nd:YAP flash-lamp pumped oscillator, and oscillator-amplifier arrangements, respectively. In this paper weprolonged our study with the goal of obtaining the higher energy from the oscillator only.
In this paper we also report new results obtained with V:YAG Q-switched diode end-pumped laser. Composite
Nd:YAG rod Q-switched by V:YAG crystal and with Nd:YAG/V:YAG monolith rod under CW longitudinal diodepumping was obtained and compared.

2. V:YAG PASSIVE SATURABLE ABSORBER
2.1. Material properties of V:YAG crystal
Matrix of pure garnet is optically neutral in the range of ultraviolet to far infrared, so that all optical effectsof doped garnet are dependent on dopant properties and ligands field symmetry. Oxygen sub-lattice of garnet
matrix is formed by dodecahedrons with the point symmetry D2 and coordination number eight populated by
Y3+ ions, octahedrons of the symmetry C3 and coordination number six, populated by Al3+ and tetrahedronsof the symmetry S4 and coordination number four, populated also by Al3+ ions. It was found, that vanadiumions V3+ substitute only Al3+ in octahedral and tetrahedral centers.18
Absorption bands at 430 nm and 600 nm are related to V3+ ion in octahedral position.13 The tetrahedrally
coordinated V3+ ion contributes to the peaks at 720 – 900 nm (max. 825 nm) and 0.9 – 1.5 µm (max. 1330 nm).
Therefore tetrahedral coordination of the ions is important for passive Q-switch at 1.064 and 1.342 µm.18 On
the other hand, the fraction of V3+ ions in tetrahedral coordinated position of V:YAG crystals grown in iridium
crucibles is less than 1 %. It was also found, that the post-growth thermal annealing in reducing atmosphere
increases the concentration of optically active V3+ ions.13 Major characteristics of V:YAG saturable absorberin comparison are summarized in Table 1. The dependence of V:YAG crystal absorption coefficient on the
wavelength is in Figure 1.
Table 1. Summary of V:YAG characteristics

V:YAG (at 1.34 µm)
9, 18

σgsa = (7.2 ± 2.6) × 10−18 cm2

Excited state absorption cross-section9, 18

σesa = (7.4 ± 2.8) × 10−19 cm2

Recovery time8, 9, 18

τr = 5 − 22 ns

Ground state absorption cross-section

11, 20Saturation intensity

Absorption coefficient18, 20

Isat = 10 − 30 MW.cm−2
α = 0.5 − 2.2 cm−1

Figure 1. Measured dependence of used V:YAG crystals absorption coefficient on the wavelength.

3. EXPERIMENTAL ARRANGEMENT
3.1. Flash-lamp pumped Nd:YAP laser
Flashlamp pumped Nd:YAP crystal rod with 5 mm diameter and 90 mm long was used as laser active media. The
both ends of the crystal were cut at angle 1◦ and were antireflection coated for both wavelength 1.08 and 1.34 µm.
The 45 cm long optical cavity was composed of concave rear mirror M1 (r = −7 m, a maximum reflectivity forthe 1.34 µm and a minimum reflectivity for 1.08 µm) and a plane output mirror M2 with the minimum reflection
on the wavelength 1.08 µm. The output mirror reflectivity R2 for the generated wavelength 1.34 µm was varied
from 40 % up to 60 % to optimize energy Eout and duration ∆τ of the output laser pulse (FWHM).
For flash-lamp pumped Nd:YAP laser switching discs of the diameter 10 mm and of the thickness 2.08 mm,
5.10 mm, 7.14 mm, and 8.0 mm were machined from V:YAG crystals. The initial transmission of used V:YAG
crystal samples was 68 %, 38 %, 28 %, and 23 %. The discs were both sides polished and AR/AR coated so that aminimum reflectivity on 1.08 and 1.34 µm was reached. The studied V:YAG saturable absorber was placed near
the rear mirror. The initial transmission of this crystal was also optimized with the regard to the output energy
and length of generated train of pulses.

Figure 2. Flash-lamp pumped Nd:YAP laser system. Nd:YAP crystal (5 mm diameter and 90 mm long) pumped in
LMI difusive reflection cavity by Xe-flash-lamp. M1 – concave rear mirror (r = −7 m) with maximum reflectivity for the
1.34 µm and a minimum reflectivity for 1.08 µm; M2 – plane output mirror with the minimum reflection on the wavelength
1.08 µm.

3.2. CW Diode pumped Nd:YAG laser – Nd:YAG composite rod
The active medium of first tested diode pumped laser was end-pumped composite Nd:YAG crystal. This YAG
crystal consists of 8 mm long active part doped by Nd3+ ions (1 at. %) and of 4 mm long undoped part – see
Figure 3. The diameter of this crystal was 5 mm. The outer frontal part of the laser crystal had broadband
antireflection coatings (AR) for the 1064 nm wavelength. The undoped part was bounded to the pumping faceof the crystal doped part. In our previous study21 we have confirmed that using of such undoped part of laser
rod enlarges the active material cooling surface and improves a laser active media thermal field uniformity andheatsink. Laser crystal was mounted in adjustable water-cooled cupreous ring. Temperature of cooling water was
not a specially stabilized and it was moving in range from 12 to 14 ◦ C.

Figure 3. Active and passive crystals used in diode pumped Nd:YAG laser. Composite Nd:YAG crystal (undoped part
4 mm, Nd3+ doped part 8 mm) and separated passive saturable absorbers (#1, d = 330 µm, T0 = 93 %;#2, d = 420 µm,
T0 = 91 %; #3, d = 520 µm, T0 = 89 %).

The pumping source used was a CW operating laser diode HLU20F400 (LIMO Laser Systems) emitting
radiation at wavelength 808 nm with the maximum output power 20 W at the end of the fiber (fiber core diameter:
400 µm; numerical aperture: 0.22). The diode radiation was focused into the active Nd:YAG crystal by two
achromatic doublet lenses with the focal length f = 75 mm. The measured diameter of pumping beam focus
inside the crystal was 360 µm. The active part of laser crystal absorbed approximately 95 % of pumping radiation.
The 80 mm long resonator of the Nd:YAG laser was formed by a planar dielectric mirror R1 with hightransmission for the pumping radiation (T > 98 % @ 808 nm) together with the high reflectance for the generated
radiation (R1 = 100 % @ 1340 nm), and by a concave (100 mm or 146 mm) dielectric mirror R2 serving as an(1)
output coupler – see Figure 4. As this coupler five various dielectric reflectors was proved: R2 = 98 % @ 1340 nm,
(4)
(3)
(2)
r = 146 mm; R2 = 94 % @ 1340 nm, r = 100 mm; R2 = 91 % @ 1340 nm, r = 146 mm; R2 = 86 % @ 1340 nm,(5)
r = 146 mm; and R2 = 82 % @ 1340 nm, r = 146 mm.

Figure 4. Longitudinaly diode pumped Nd:YAG laser system Q-switched by independent V:YAG crystal. M1 – rear(pumping) resonator flat mirror, M2 – curved output coupler.

For the Q-switching three samples of V:YAG crystals with different initial transmission were used. The
diameter of used discs was 7 mm and the thickness was 320, 410 and 520 µm. Corresponding initial transmissionof used V:YAG crystal samples was 93 %, 91 %, and 89 %. These discs were also both sides polished and AR/ARcoated to obtain a minimum reflectivity on 1.08 and 1.34 µm. This crystals were fixed in adjustable air-cooled
cupreous ring and placed in the laser resonator between laser crystal and output coupler – see Figure 4.

3.3. CW Diode pumped Nd:YAG/V:YAG monolith laser
For the construction of longitudinally diode pumped Q-switched Nd:YAG laser operating at wavelength 1340 nm
a specially developed sandwich crystal was tested. This crystal combine in one piece cooling undoped part
(undoped YAG crystal), active laser part (YAG crystal doped with Nd3+ ions) and saturable absorber (YAG
crystal doped with V3+ ions) – see Figure 5. The undoped YAG and Nd3+ doped part of this crystal is exactly
the same like in the previous case described in subsection 3.2, that means that the diameter of this crystal, thelengths of undoped, and the lengths of Nd3+ doped part was 5 mm, 4 mm, and 8 mm, respectively. The thickness.
of the V:YAG part was 530 µm and its initial transmission was approximately T0 = 88 %. This value was set upon the base of previous experiment results to be sure, that the system reach the threshold. The outer frontal
part of the laser crystal had broadband antireflection coatings (AR) for the wavelength 1064 nm and 1340 nm.
The undoped part was bounded to the pumping face of the crystal doped part.
This combination of active crystal and saturable absorber in one monolithic part allows us to realize morecompact resonator. The shortest tested resonator, limited by the optics and crystal mount, was only 33 mm long
– see Figure 6. The pumping laser diode, cooling system, and laser output couplers were the same like in previous
case.

Figure 5. Nd:YAG/V:YAG monolith crystal used in diode end-pumped laser: undoped part 4 mm, Nd3+ doped part
8 mm and V3+ doped part 530 µm (T0 = 88 %).

Figure 6. Longitudinaly diode pumped Q-switched laser based on Nd:YAG/V:YAG monolith crystal. M1 – rear (pumping)resonator flat mirror, M2 – curved output coupler.

3.4. Methods of characterization
The time characteristics were measured with the help of a fast vacuum photodiode. With this photodiodeTektronix oscilloscope TDS 3052B (500 MHz, 5 GS/s) or the S7-19 oscilloscope (7 GHz) were used. A computeroperated two channel Molectron JD 2000 Joulemeter with two thermal detectors (Gentec ED-200LA, voltage
responsivity 1.87 V/J; Molectron J25, voltage responsivity 8.59 V/J) was used for the energy measurements. The
output power was obtained by Molectron energy/power meter EMP 2000 with two Molectron PowerMax probes(PM10 and PM3). A spectrum of the generated radiation was investigated with the help of an IR wavelength
meter (StellarNet EPP 2000).

4. EXPERIMENTAL RESULTS
4.1. Flash-lamp pumped Nd:YAP laser
Four V:YAG samples were investigated in order to maximize output power and to obtain the best pulse stabilityof flash-lamp pumped Nd:YAP mode-locked/Q-switched laser. The initial transmissions of available samples at
1.34 µm were T0 = 68 %, 38 %, 28 %, and 23 %. The lamp driving power was chosen for just-above-thresholdoperation in order to generate the single Q-switched/mode-locked pulse train. The dependence of the output
energy and of the mode-locked pulse train duration on the initial transmission of the V:YAG saturable absorber
was measured.
A full modulation was observed with three samples with initial transmission in the range of 28 – 68 %.
The initial transmission of the fourth samples (T0 = 23 %) was to low to obtained laser emission with used laser
pump source. The highest energy for one generated train of pulses was reached for the initial V:YAG transmission
T0 = 28 %. For this initial transmission the output oscillator energy, and the corresponding pulse train duration
was 53 mJ, and 17 ns, respectively. The train of pulses corresponding to T0 = 28 % is in Figure 7, left. For themeasurement of the individual pulse duration in train the vacuum photodiode (CTU) and 7 GHz oscilloscope
S7-19 with a CCD readout was used — Figure 7, right. The value measured is around 1 ns.

Figure 7. Flash-lamp pumped Nd:YAP laser modelocked by V:YAG absorber — train of pulses (left, 5 ns/div, 0.5 GHz)and single pulse (right, 1 ns/div, 7 GHz) temporal development. Resonator length 45 cm, V:YAG initial transmission
T0 = 28 %, output coupler reflectivity ROC = 60 % .

4.2. CW Diode pumped Nd:YAG laser – Nd:YAG composite rod
In free-running regime (without passive Q-switch inside the resonator) constructed Nd:YAG laser was operatingwith all five available output couplers (ROC = 82, 86, 91, 94, and 98 % – see subsection 3.2). From measured
dependencies of generated output power at wavelength 1342 nm (pump power at 808 nm) it was found that
optimum output coupler reflectivity is between 87 and 90 %. The maximum output power 1.6 W @ 1340 nm(absorbed pumping power 10 W) was reached in CW free-running regime with output coupler reflectivity 91 %.
The differential efficiency was better than 20 %.
For Q-switching regime there were tested 15 possible combinations of the output coupler reflectivity (fiveoutput couplers) and passive Q-switch initial transmissions (3 V:YAG samples), but only for the eight combinations the laser emission was reached. For these cases following parameters of Nd:YAG laser output radiation in
dependence on pumping power were measured: a mean output power, generated giant pulse width (FWHM), andrepetition rate of generated pulses. From obtained values, single pulse energies and peak powers were calculated.
Results are summarized in Table 2. Examples of generated Q-switched pulses are shown on Figure 8.
It was found, that the shortest pulses (21 ns) are generated when the saturable absorber with the lowest
initial transmission (88 %) was used. This absorber was operating only together with the output coupler having
the reflectivity 94 % and the corresponding peak mean power, single pulse energy and peak power were 215 mW,
64 µJ, and 3.1 kW, respectively. Longer but more powerful pulses were generated when the output coupler having

close optimal reflectivity 91 % was used. The generated pulse lengths were 30 ns and 25 ns for V:YAG saturable
absorbers with T0 = 93 %, and T0 = 91 %, respectively. In these cases, the higher mean power (525 mW for
T0 = 93 %, and 365 mW for T0 = 91 %) was reached which corresponds to higher pulse energy (118 µJ for
T0 = 93 %, and 126 µJ for T0 = 91 %) and higher peak power (4.3 kW for T0 = 93 %, and 4.8 kW for T0 = 91 %).
Table 2. CW diode pumped Nd:YAG laser parameters – Nd:YAG composite rod, separated V:YAG saturable absorber.
Dependence of generated radiation parameters on the output coupler reflectivity ROC and saturable absorber initialtransmission T0 .

Mirror

V:YAG

Mean

Pulse

Pulse

Peak

Pulse

reflectivity

transmission

power

width

energypower

frequency

ROC [%]

T0 [%]

P [mW]

FWHM [ns]E [µJ]

Ppeak [kW]f [kHz]

98

93

188

36

64

1.7

16.0

98

91

186

28

68

2.4

7.8

94

93

308

37

22

0.6

14.0

94

91

270

26

53

2.0

7.1

94

89

215

21

64

3.1

5.6

91

93

525

30

126

4.3

11.0

91

91

365

25

118

4.8

5.3

86

93

306

31

84

2.7

4.9

Figure 8. CW Diode pumped Nd:YAG laser parameters – Nd:YAG composite rod, separated V:YAG saturable absorber. Time structure of generated radiation in large scale and in detail. Output coupler reflectivity 94 %, V:YAG initialtransmission T0 = 89 %, resonator length 80 mm.

4.3. CW Diode pumped Nd:YAG/V:YAG monolith laser
On the base of previous experiments, a special crystal monolith based on YAG combining in one block undoped
cooling part, Nd3+ doped active laser crystal, and V3+ passive saturable Q-switch, was designed and realized(Figure 5). The initial transmission of used saturable absorber was set to 88 %. This crystal was tested withall possible output couplers (ROC = 94 %, 91 %, 86 %, and 82 %) except of output coupler with reflectivity
98 % to prevent dielectric coatings damage. Constructed longitudinally diode CW pumped laser was operatingwith all these mirrors. More compact system allows us to use shorter laser resonator – three different lengths

were tested: 54 mm, 42 mm, and 33 mm. Like in previous case, following parameters of Nd:YAG laser output
radiation in dependence on pumping power were measured: a mean output power, generated giant pulse width(FWHM), and repetition rate of generated pulses. From obtained values, single pulse energies and peak powers
were calculated. Results are summarized in Table 3. Examples of generated Q-switched pulses are shown on
Figure 9.
From results it follows, that in case of this compact laser more stable CW Q-switched output at wavelength
1340 nm was obtained. Generated pulse lengths were in range between 11 na 20 ns and depends mainly on
resonator lengths – it did not changed significantly with pumping power and with output coupler reflectivity.
Duration of shortest pulses obtained with resonator length 33 mm was only 11 ns. Maximum obtained mean
power, peak power, and pulse energy at wavelength 1340 nm was 0.7 W, 6.1 kW, and 97 µJ, respectively.
Table 3. CW diode pumped Nd:YAG laser parameters – Nd:YAG/V:YAG monolith rod. Dependence of generated
radiation parameters on the output coupler reflectivity ROC and resonator length L.

OutputResonator

Mean

Pulse

Peak

Pulse

Pulse

couplerlength

power

width

power

energyfrequency

ROC

L [mm]

P [mW]

FWHM [ns]Ppeak [kW]E [µJ]

f [kHz]

94 %

54

360

19.6 ± 0.7

4.3

78

4.6

91 %

54

570

19.3 ± 0.4

4.8

96

5.9

86 %

54

500

19.7 ± 0.3

5.0

97

5.2

82 %

54

510

19.6 ± 1.5

4.7

90

5.7

91 %

42

700

14.7 ± 0.5

4.6

67

10.4

82 %

42

580

14.4 ± 0.6

4.9

68

8.5

82 %

33

500

12.0 ± 0.5

4.9

58

8.6

82 %

33

430

11.0 ± 0.4

6.1

67

6.4

Figure 9. CW diode pumped Nd:YAG laser parameters – Nd:YAG/V:YAG monolith rod. Time structure of generated
radiation in large scale and in detail. Output coupler reflectivity 82 %, V:YAG initial transmission 88 %, resonator length
33 mm.

5. DISCUSSION
5.1. Flash-lamp pumped Nd:YAP laser
The laser oscillator optimal performance of the flash-lamp pumped Nd:YAP laser Q-switched/mode-locked by
V:YAG saturable absorber was found by varying the initial saturable absorber transmission and the resonator
length. The highest energy for one generated train of pulses was reached for the initial V:YAG transmission
T0 = 28 %. The output oscillator energy was 53 mJ, the corresponding pulse train duration was 17 ns. The lengthof single pulse in train was around 1 ns (FWHM).

5.2. Diode pumped Nd:YAG lasers
V:YAG saturable absorber was also tested for Q-switching of diode end-pumped Nd:YAG laser with short cavity.
Two similar configurations, mainly differing in active crystal and saturable absorber position, were tested andcompared.
In the first configuration as an active medium the composite Nd:YAG crystal was used. This crystal consists
of YAG undoped cooling part and Nd3+ ion doped gain part – Figure 3). Used V:YAG saturable absorber wasplaced in the laser resonator separately in its own holder – see Figure 4.
In the second configuration specially prepared Nd:YAG/V:YAG monolith crystal was tested as the active
medium. This crystal interconnect the Nd:YAG laser gain medium, YAG undoped cooling part and V:YAG
saturable absorber in one compact piece – Figure 5).
The first configuration (separated gain medium and saturable absorber) allow us to change simply the initialtransmission of used saturable absorber and to optimize the laser configuration. Several suitable conbinationsof saturable absorber initial transmissions and output coupler reflections were found. For resonator length of
80 mm (limited by mounting elements), the shortest obtained pulses were 21 ns long (FWHM) (the output
coupler reflectivity and V:YAG initial transmission was ROC = 94 %, and T0 = 89 %, respectively). In this case,mean power, peak power, and pulse energy was 215 mW, 3.1 kW, and 64 µJ, respectively. The highest mean power(525 mW) and pulse energy (126 µJ), but longer pulses (30 ns) were obtained for ROC = 91 % and T0 = 93 %.
The highest peak power (4.8 kW) reached in this configuration was obtained for ROC = 91 %, and T0 = 91 %.
The second configuration of diode pumped laser system, based on Nd:YAG/V:YAG monolith crystal, allowed
us to use shorter external resonator (up to 33 mm), but low level signal transmission of saturable absorber
was fixed to value T0 = 88 %. This value (as was explained in subsection 3.3) was set on the base of results
obtained in experiment made with separated V:YAG saturable absorbers. This initial transmission is a little bit
lower than the lowest value of tested separated V:YAG crystal (T0 = 89 %). While the laser Q-switched by thisseparated V:YAG absorber was operating together with output coupler with reflectivity ROC = 94 % only, the
Nd:YAG/V:YAG monolith crystal was operated in the laser resonator designed with all tested output couplers(ROC = 82 − 94 %). The generated pulse parameters depends mainly on resonator length and it did not changed
significantly with pumping power and with output coupler reflectivity. These parameters affect mainly the mean
power and the pulse repetition rate. Duration of shortest pulses obtained with resonator lengths 33 mm was only
11 ns. Maximum obtained mean power, peak power, and pulse energy at wavelength 1340 nm was 0.7 W, 6.1 kW,
and 97 µJ, respectively.

6. CONCLUSION
Passive Q-switching provides a successful and compact means of generating short, high-intensity laser pulses.
V:YAG crystals grown in reducing atmosphere have higher concentration of V3+ tetrahedrally coordinated ions,that effect in more intense absorption bands and lower parasitic nonsaturable losses in comparison to V:YAG
crystals grown in iridium crucibles. Various samples of the saturable absorbers were grown and experimental
observations were given with the goal of finding the optimal laser system configuration.
It could be summarized that the laser oscillator optimal performances were found for flashlamp as well as diodepumped laser Q-switched by V:YAG saturable absorber. From the point of the applications both systems areuseful. The highest energy – 50 mJ – in Nd:YAP flashlamp pumped laser oscillator obtained with the transmission
T0 = 28 % of V:YAG could be useful in the system of Raman laser which can generate eye safe 1.5 µm wavelength.

Diode pumped laser can be used in the future for the technological laser systems. Comparing the the
Nd:YAG/V:YAG monolith system with the same but “non-contact” configuration case (when the saturable
absorber is separately from the active medium) some significant advantages of monolith arrangement for all
future applications are seen:• Simplest Q-switched laser system construction and adjustment, shorter laser resonator ⇒ more compact
laser system, smaller sensitiveness to all mechanical disturbance, rugged and low-maintenance system,
generation of shorter pulses.
• Contact of V:YAG saturable absorber with the rest of the monolith crystal inherently increase its coolingand improve thermal stability of all system ⇒ higher temporal stability of generated radiation (mean power
and pulse frequency stability, pulse-to-pulse stability.)• The simple arrangement of laser active-passive medium (the connection of two originally independent
optical elements) result in the reduction of the inside resonator losses ⇒ lower obtained threshold, possibilityof using the output mirror with lower reflection, higher power done by shorter length of generated pulse.
• Other improvement of monolith scheme can be expected in the case when the resonator mirrors will be
implemented directly on the crystal faces ⇒ microchip laser based system.

ACKNOWLEDGMENTS
This research has been supported by the Czech Ministry of Education – Grant No. 210000022, and by the Czech
Ministry of Industry and Trade – Project No.: FF–P/125.

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