1. Ken-Chia Chang, and Ming-Dar Wei* * mdwei@mail.ncku.edu.tw
Generation and transformation of azimuthal and radial polarization in a typically three-element Nd:GdVO4 laser
Ken-Chia Chang, and Ming-Dar Wei*
Department of Photonics, National Cheng Kung University, No.1, University Road, Tainan City 701, Taiwan *
AUG. 19, 2014

2. Outline What is the Cylindrical Vector (CV) beam and its applications
An overview of Developments of CV beam
Previous studies of CV beam under different cavity
configurations in our laboratory
Intra-cavity axicon (hemispherical cavity)
The pulse laser with CV polarization by designing resonator
(three-element cavity)
Pump profile shaping with axicon and lens (microchip laser)
Experiment setup and results
Discussion and conclusion
Outline

3. What is the CV beam and its applications
Unique Properties ：
Strong and localized longitudinal field
component
Small spot size by using tightly focused
Phys. Rev. Lett. 91, (2003).
Opt. Commun. 179, 1 (2000).
Applications ：
High-Resolution Imaging
Plasmon Excitation
Laser Machining
Nanoparticle Manipulation
Adv. Opt. Photon. 1, 1 (2009).
Radial polarization
Azimuthal Polarization
Electric vector field

4. Reviews Cylindrical vector beam Passive Superposition
Special-fabricated devices
Active
Birefringence
Inherent
Form birefringence
Thermal-induced
Brewster axicon
Polarization selector
Reviews

5. Plano-concave cavity configuration with intra-cavity axicon
azimuthal polarization (Zo)
radial polarization (Ze)
K. -C. Chang, T. Lin, and M. -D. Wei*, Opt. Express, 21, (2013).

6. The characteristics of AP ring with pulsed output in a three-element cavity configuration
Condition ： z1 = 20 cm
z2 = 12.3 cm
Cr4+:YAG
K. -C. Chang, D. -L. Li and M. -D. Wei*, JOSA B 31, 382 (2014).

7. Schematic of microchip laser
Z0 = 83 mm
△Z = 5.91 mm
M. -D. Wei*, Y. S. Lai and K. -C. Chang, Opt. Lett. 38, 2443 (2013).

8. Experiment setup and the analysis of stable region with a fixed z1
Laser crystal ： 3*3*8 mm3，
1 at.% -doped， nm
M1 nm ; nm
L ：f = 75 nm
M2(OC) ：R = 91%
z1=20 cm
12.148 ≦ z2 ≦  cm
Prefer generating AP
34.248 ≦ z2 ≦34.754cm
Prefer generating RP
12.148 ≦ z2 ≦  cm

9. The results of pattern formation
z1 = 20 cm
Pump power = 4W

10. Intensity distributions of ring patterns generated from the cavity when the z2 was changed
(c) z2= cm
(b) z2= cm
(a) z2= cm N
12.175
12.235
z2 (cm) AP
UnP RP
12.280
12.300
12.335
12.385

11. Measurement method 30° Degree of Polarization (DOP) 60° 90°
Power meter
Polarizer
slit 300 mm
30°
60°
90°
1. Selecting the measured portion of
the pattern
2. Passing through the polarizer
3. Measuring the power by using the
power meter
4. Determining the polarization direction and
degree of polarization by using the fitting curve
Degree of Polarization (DOP)
define： (Imax - Imin) / (Imax + Imin)
The orientation of the slit is −30°
The red line is the fitting curve with
the sin2 function

12. The characteristics of AP and RP ring
Case: AP
Case: RP
Slope = 1.019 ± 0.005
Average DOP = 92.20% ± 1.99%
Slope = 0.999 ± 0.006
Average DOP = 96.30% ± 0.87%

13. The quality of CV polarization
The position of z2 (cm)
Mode type
  Degree of Polarization
(DOP)
Slope efficiency
Lasing threshold
12.200 AP
96.30% ± 0.87%
39.0%
1.61W
12.290 RP
92.20% ± 1.99%
38.6%
1.45W
12.360
93.70% ± 1.46%
36.7%
1.31W
Why the polarization transformation can be observed?

14. Considering extraction efficiency for both rays
12.175
12.235
z2 (cm) AP
UnP RP
12.280
12.30
12.335
12.385

15. Conclusion
We have generated the cavity-length-dependent variation of polarization states from the unstable to stable region in a diode-pumped Nd:GdVO4 laser with a three-element cavity.
By considering the extraction efficiency from pump energy and the variation of spot size in the gain medium for o-ray and e-ray, mechanism of polarization transformation is discussed.

16. Thanks for
your attention!!