yvo4/nd:yvo4/yvo4 self-raman laser at 1,764 nm

YVO4/Nd:YVO4/YVO4 self-Raman laser at 1,764 nm

Chenlin Du • Xiaohua Xie • Yufeng Zhang •

Guoxi Huang • Yongqin Yu • Dongdong Wang

Received: 31 May 2013 / Accepted: 21 November 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract A diode-end-pumped composite YVO4/

Nd:YVO4/YVO4 crystal self-Raman laser at the second-

Stokes wavelength of 1,764 nm is demonstrated. The

maximum average output power of second-Stokes radiation

was up to 0.99 W at a pump power of 34 W and a pulse

repetition frequency of 20 kHz, corresponding to an optical

conversion efficiency of 2.9 %. The highest peak power

and the shortest pulse duration were 21.5 kW and 1.92 ns,

respectively.

1 Introduction

Stimulated Raman scattering (SRS) in crystal materials has

been shown to be an efficient method to extending the laser

wavelengths from the ultraviolet to the near infrared. Self-

Raman lasers, in which the laser crystal acts as the Raman-

active medium simultaneously, can provide multiple

advantages of small scale, low loss and high efficiency.

Nowadays, the materials most commonly used in Raman

lasers include YVO4, GdVO4, LiNbO3, Ba(NO3)2, BaWO4,

KGd(WO4)2 and SrWO4. Of the Raman-active media, the

neodymium-doped yttrium orthovanadate crystal

(Nd:YVO4) was considered as a wonderful Raman medium

due to its high Raman gain (4.5 cm/GW) [1] and large

emission cross section.

In 2001, Kaminskii et al. [1] predicted that Nd:YVO4

and Nd:GdVO4 would be promising self-Raman laser

media. Before long, it was first experimentally proved by

Chen [2, 3]. In recent years, solid-state Raman lasers

based on Nd:YVO4 crystal has been widely developed

[4–7]. In those studies, major attention was focused on

the generation of the first-Stokes laser or the visible laser

combining with frequency-doubling technology. In 2012,

Chen et al. [8] investigated second-Stokes YVO4/

Nd:YVO4/YVO4 self-Raman laser operating at the

wavelength of 1,313 nm for the first time. However, as

far as we know, to date there has been no relevant report

on second-Stokes self-Raman laser at 1.76 lm with

Nd:YVO4. The other methods for generating 1.7 lm laser

include solid-state laser with Er3?-doped crystal or in-

tracavity optical parametric oscillators based on KTiO-

AsO4 or periodically poled lithium niobate media [9–11].

The disadvantages of the later approach are either the

complex experimental setup or the necessary special

crystal temperature control. The laser sources operating

at the eye-safe region of the spectrum (1.5–1.8 lm) are of

great interest for various potential applications such as

laser ranging, remote sensing and active imaging. The

self-Raman laser with the advantages of compact struc-

ture and high efficiency will attract more and more

attention.

The thermal effects, which are caused by the absorption

of pump light and the SRS cascading frequency conversion

C. Du (&) � X. Xie � Y. Zhang � G. Huang � D. Wang

College of Electronic Science and Technology, Shenzhen

University, Shenzhen 518060, People’s Republic of China

e-mail: [email protected]

C. Du � X. Xie � Y. Zhang � G. Huang � Y. Yu � D. Wang

Shenzhen Key Laboratory of Laser Engineering,

Shenzhen 518060, People’s Republic of China

C. Du � X. Xie � Y. Zhang � G. Huang � Y. Yu � D. Wang

Key Laboratory of Advanced Optical Precision Manufacturing

Technology of Guangdong Higher Education Institutes,

Shenzhen University, Shenzhen 518060,

People’s Republic of China

Y. Yu

College of Physics Science and Technology, Shenzhen

University, Shenzhen 518060, People’s Republic of China

123

Appl. Phys. B

DOI 10.1007/s00340-013-5735-4

process in the Nd:YVO4 crystal, are the most important

factors affecting the overall performance of the self-Raman

laser. To reduce the influence of the thermal effects, one

effective method is using the composite Nd:YVO4 crystal

as the laser gain medium [12]. Therefore, a 30-mm-long

double-end diffusion-bonded composite Nd:YVO4 crystal

was employed in our work that not only mitigated the

thermal effects but also increased the Raman interaction

length for the SRS frequency conversion.

In this paper, an all-solid-state self-Raman second-

Stokes laser at 1,764 nm is demonstrated with a diode-

pumped actively Q-switched composite YVO4/Nd:YVO4/

YVO4 crystal laser. With the incident power of 34 W at a

repetition rate of 20 kHz, the maximal average output

power of second-Stokes radiation at 1,764 nm was up to

0.99 W, corresponding to an optical conversion efficiency

of 2.9 %. The shortest pulse width was 1.92 ns, and the

maximal peak power was 21.5 kW.

2 Experimental setup

The diode-pumped second-Stokes self-Raman laser

experiments were carried out in a plano-concave resonator,

as shown in Fig. 1. The pump source was a commercially

available high-power fiber-coupled diode-laser-array at

808 nm. The core diameter and numerical aperture (N.A.)

of the fiber were 0.4 mm and 0.22, respectively. The pump

beam from the fiber end at the wavelength of 808 nm was

focused into the laser crystal with the spot size of 0.4 mm

in diameter by an optical imaging system with the imaging

ratio of 1:1. The composite YVO4/Nd:YVO4/YVO4 crystal

was a 0.3 at % Nd3?-doped 10-mm-long a-cut Nd:YVO4

crystal bounded with a 2-mm-long pure YVO4 at the

pumped end and a 18-mm-long pure YVO4 at another end.

It was anti-reflection (AR) coated at 808, 1,064 and

1,342 nm on both of its faces. And the transmittances of

the laser crystal at 1,524 and 1,764 nm were measured to

be 91 and 70 %, respectively. The absorption efficiency of

the incident pump power was measured to be about 95 %.

To remove the heat generated in the laser crystal, it was

wrapped with indium foil and mounted in a water-cooled

Fig. 1 Schematic diagram of

the composite Nd:YVO4 crystal

second-Stokes self-Raman laser

16 20 24 28 32 360

200

400

600

800

1000

Ave

rage

out

put

pow

er a

t 17

64 n

m (

mW

)

Incident pump power (W)

20 kHz

25 kHz

30 kHz

Fig. 2 Average output power at 1,764 nm versus the incident pump

power for PRFs of 20, 25 and 30 kHz

Fig. 3 The optical spectrum of the actively Q-switched composite

YVO4/Nd:YVO4/YVO4 self-Raman laser

C. Du et al.

123

copper block heat sink. And the water temperature

was maintained around 18 �C during the experiments.

A compact resonator with a total length of 108 mm was

designed for second-Stokes light generation. The front

mirror M1 was a concave mirror with a radius of curvature

of 250 mm, high-transmittance (HT) coated at 808 nm and

high-reflection (HR) coated at 1,342, 1,524 and 1,764 nm.

A flat output coupler M2 was HR coated at 1,342 and

1,524 nm, and HT coated at 1,764 nm. A 46-mm-long

acousto-optic Q-switch (AOS, Gooch & Housego Co.) was

AR coated at 1,342 and 1,524 nm. And its transmittance at

1,764 nm was measured to be 90 %. To suppress parasitic

oscillations at the 1.06 lm region, all of the elements in the

cavity were high-transmittance (HT) coated at 1.06 lm.

3 Results and discussion

With the above-mentioned experimental configuration, the

second-Stokes average output power at 1,764 nm with

respect to the incident pump power has been investigated at

different pulse repetition frequencies (PRFs) of 20, 25 and

30 kHz, as shown in Fig. 2. Since the second-Stokes output

power was very sensitive to the duty cycle of the Q-switch,

the duty cycle was optimized first of all. At the PRF of

20 kHz with the duty cycle of 0.79 % for Q-switch opera-

tion, the maximum second-Stokes average output power was

up to 0.99 W with an incident power of 34 W and a corre-

sponding optical conversion efficiency of 2.9 %. The max-

imum pulse energy was calculated to be 49.5 lJ. The

16 20 24 28 32 36

2

4

6

8

10

12

14 1342 nm 1524 nm 1764 nm

Pul

se d

urat

ion

(ns)


(a)

(b) (c)

(d)

Fig. 4 a Pulse duration for

fundamental (1,342 nm), first-

(1,524 nm) and second-Stokes

radiation (1,764 nm) with

respect to the incident pump

power at PRF of 20 kHz;

b–d typical temporal pulse

profiles for three wavelengths at

pump power of 24 W and the

PRF of 20 kHz


123

threshold pump powers of first- and second-Stokes radiation

were measured to be 8 and 12.3 W, respectively. At the

pump power from 9 to 16 W, the major portion of the output

radiation was the first-Stokes output. When the pump power

was over 17 W, the second-Stokes line increased rapidly to

be the major portion of the output radiation due to the effi-

cient conversion from first-Stokes line. At the PRFs of 25

and 30 kHz, the maximum second-Stokes average output

powers were up to 0.863 and 0.607 W, respectively.

We noted that the PRFs could affect the characteristics of

the second-Stokes average output power directly. At the

smaller PRF, there had been enough time for the population

inversion reaching its peak value during two adjacent pulses.

Hence, the extremely high peak power of the fundamental

pulse could be generated, which enhanced the SRS cascaded

conversion efficiency and resulted in the greater second-

Stokes average output power eventually. For this reason, we

obtained the maximum second-Stokes average output powers

at the PRF of 20 kHz. The output power tended to saturate at

the maximum level due to the resonator instability caused by

strong thermal lens effect resulting from the SRS conversion

process [13, 14]. There were several reasons for the low

optical conversion efficiency. Firstly, the stimulated emission

cross section of the Nd:YVO4 crystal at 1,342 nm was smaller

compared with that at 1,064 nm. Secondly, the laser crystal

and the Q-switcher were not AR coated at 1,764 nm, which

resulted in more loss in the cavity. Finally, the optimization of

the output coupling would be beneficial to the higher con-

version efficiency. The fundamental radiation was measured

to be linearly polarized along the p-direction, so did the first-

and second-Stokes radiation. The polarized output has the

advantage that it avoids undesirable thermally induced bire-

fringence [15] and improves the Raman conversion efficiency

[16, 17]. The laser average output power instability was

measured to be 1.95 % for 36 min with an incident power of

34 W and the PRF of 20 kHz.

The spectrum information of the second-Stokes laser

was monitored by an optical spectrum analyzer (Yokogawa

AQ6375). As shown in Fig. 3, the optical spectrum was

recorded at the incident pump power of 34 W and a PRF of

20 kHz. The central wavelengths of the fundamental, first-

and second-Stokes radiation were measured to be 1,342.43,

1,524.67 and 1,764.24 nm, with the corresponding line

widths of 0.16, 0.18 and 0.27 nm, respectively. It can be

seen that the frequency shift of each adjacent wavelengths

interval was about 890 cm-1, which was the optical

vibration modes of the tetrahedral VO43- ionic groups

(890 cm-1). The optical spectrum indicates that very small

residual of fundamental emission and first-Stokes Raman

emission was present in the output.

A grating monochromator was applied to separate the

fundamental, first- and second-Stokes output radiation. The

temporal pulse behavior was recorded by a mixed signal

oscilloscope (Tektronix MSO 4032) with a fast photodiode

detector (EOT ET-3500). The pulse widths of the funda-

mental, first- and second-Stokes radiation, as shown in

Fig. 4a, were measured as a function of the incident pump

power at the PRF of 20 kHz. The shortest pulse width of

second-Stokes was measured to be 1.92 ns with a pump

power of 24 W corresponding to the fundamental and the

first-Stokes pulse width of 9.8 and 5.83 ns, respectively, as

shown in Fig. 4b–d. The pulse shortening was due to the

cascading nonlinear frequency conversion process of SRS

[18, 19]. It can also be seen that the pulse width of higher-

order Stokes radiation is shortened much more.

The second-Stokes output beam profiles were measured

by a CCD camera (Spiricon PY-III), as shown in Fig. 5a.

1600 1760 1920 2080 22400

800

1600

2400

3200

4000

4800

Width X - Horizontal directionWidth Y - Vertical directionFitted Curve - Horizontal directionFitted Curve - Vertical direction

Bea

m w

idth

(µ

m)

Z location along the axis of propagation (mm)

M2x = 1.43

M2y = 1.45

(b)

(a)

Fig. 5 a Measured beam profile of second-Stokes emission at

1,764 nm; b measured beam widths and the resulting curve fits of

the beam propagation equation

C. Du et al.

123

The beam quality factor (M2) of the second-Stokes was

measured to be 1.43 9 1.45 in the horizontal and vertical

directions at the incident pump power of 30 W and the PRF

of 20 kHz. It indicated that the second-Stokes radiation

was mainly contributed by TEM00 mode. As shown in

Fig. 5b, the artificial X and Y beam widths plotted against

their Z-axis sample locations. The beam widths were

plotted in micrometers (lm) and the Z values in millimeters

(mm). The solid lines were the resulting curve fits of the

beam propagation equation according to the plotted data.

Figure 6 shows the peak power of second-Stokes radiation

as a function of the incident pump power at different PRFs.

The highest peak power was up to 21.5 kW at the pump

power of 34 W and PRF of 20 kHz, with the corresponding

single pulse energy of 49.5 lJ. At the same incident pump

power, we can see that the single pulse energy and the peak

power with a PRF of 20 kHz are both greater than that with

PRFs of 25 and 30 kHz.

4 Conclusions

In summary, the second-Stokes self-Raman radiation at

1,764 nm was achieved in a diode-end-pumped actively

Q-switched composite YVO4/Nd:YVO4/YVO4 crystal

laser. At the pump power of 34 W and PRF of 20 kHz, the

maximum average output power was obtained to be

0.99 W, corresponding to the optical conversion efficiency

of 2.9 %. The shortest pulse width was 1.92 ns, and the

highest peak power and pulse energy were 21.5 kW and

49.5 lJ, respectively. Note that the laser crystal and the

Q-switcher are not AR coated at 1,764 nm. Thus, it is

expected that a higher output power of second-Stokes

radiation can be achieved with 1,764 nm HT-coated laser

crystal and the Q-switcher.

Acknowledgments This work was supported by the National Nat-

ural Science Foundation of China (No. 10804074, No. 61308055), the

Science and Technology Project of Shenzhen (No. JCYJ201303261

13421781, JCYJ20120613105141482, JC201005280473A), and the

Specialized Research Fund for the Doctoral Program of Higher

Education (No. 20124408120004).

References

1. A.A. Kaminskii, K. Ueda, H.J. Eichler, Y. Kuwano, H. Kouta,

S.N. Bagaev, T.H. Chyba, J.C. Barnes, G.M.A. Gad, T. Murai, J.

Lu, Opt. Commun. 194, 201 (2001)

2. Y.F. Chen, Opt. Lett. 29, 1915 (2004)

3. Y.F. Chen, Appl. Phys. B 78, 685 (2004)

4. S.H. Ding, X.Y. Zhang, Q.P. Wang, F.F. Su, P. Jia, S.T. Li, S.Z.

Fan, J. Chang, S.S. Zhang, Z.J. Liu, IEEE J. Quantum Electron.

42, 927 (2006)

5. Y.T. Chang, K.W. Su, H.L. Chang, Y.F. Chen, Opt. Express 17,

4330 (2009)

6. H.Y. Zhu, Y.M. Duan, G. Zhang, C.H. Huang, Y. Wei, H.Y.

Shen, Y.Q. Zheng, L.X. Huang, Z.Q. Chen, Opt. Express 17,

21544 (2009)

7. C.L. Du, L. Zhang, Y.Q. Yu, S.C. Ruan, Y.Y. Guo, Appl. Phys. B

101, 743 (2010)

8. W.D. Chen, Y. Wei, C.H. Huang, X.L. Wang, H.Y. Shen, S.Y.

Zhai, S. Xu, B.X. Li, Z.Q. Chen, G. Zhang, Opt. Lett. 37, 1968

(2012)

9. N.P. Barnes, R.E. Allen, L. Esterowitz, E.P. Chicklis, M.G.

Knights, H.P. Jenssen, IEEE J. Quantum Electron. QE-22, 337

(1986)

10. K.C. Burr, C.L. Tang, M.A. Arbore, M.M. Fejer, Opt. Lett. 22,

1458 (1997)

11. X.Y. Peng, L. Xu, A. Asundi, IEEE J. Quantum Electron. 41, 53

(2005)

12. Y.T. Chang, Y.P. Huang, K.W. Su, Y.F. Chen, Opt. Express 16,

21155 (2008)

15 18 21 24 27 30 33 360

8

16

24

32

40

48

Sing

le p

ulse

ene

rgy

at 1

764

nm (

µJ)


20 kHz

25 kHz

30 kHz

(a)

16 20 24 28 32 360

3

6

9

12

15

18

21

Pea

k po

wer

at

1764

nm

(kW

)


20 kHz

25 kHz

30 kHz

(b)

Fig. 6 a Single pulse energy and b peak power at 1,764 nm versus the incident pump power for different PRFs


123

13. A.J. Lee, H.M. Pask, P. Dekker, J.A. Piper, Opt. Express 16,

21958 (2008)

14. A.J. Lee, J.P. Lin, H.M. Pask, Opt. Lett. 35, 3000 (2010)

15. W. Koechner, Solid-state laser engineering, chap 10, 5th edn.

(Springer, New York, 1999)

16. J.J. Zayhowski, C. Dill, Opt. Lett. 20, 716 (1995)

17. R.A. Fields, M. Birnbaum, C.L. Fincher, Appl. Phys. Lett. 51,

1885 (1987)

18. Y.B. Band, J.R. Ackerhalt, J.S. Krasinski, D.F. Heller, IEEE J.

Quantum Electron. 25, 208 (1989)

19. H.M. Pask, Prog. Quantum Electron. 27, 3 (2003)

C. Du et al.

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yvo4/nd:yvo4/yvo4 self-raman laser at 1,764 nm

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