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					   All-solid-state Q-switched laser
   and Random laser

A: LD-single-end-pumped all-solid-state AO Q-switched Nd:YVO4 laser

B: LD-side-pumped Nd:YAG all-solid-state EO Q-switched laser

C: Random laser


                         Prof. Sun XiaoHong

     Henan Key Laboratory of Laser and Opto-Electric Information
          Technology, Zhengzhou University, Henan, China
Laser-diode (LD) pumped solid-state laser is a new
laser device with advantages of compactness, good
stabilization, high efficiency and long lifetime. It is
widely used in the fields of laser radar, material
processing, fiber communication and medical health. It
has become one of the international key development
direction.
A: LD-single-end-pumped all-solid-state AO
(Acousto-Optic) Q-switched Nd:YVO4 laser




              Fig. 1 The Z-shape cavity A-Q switched system

The advantages of Z-shape cavity are separation of the laser crystal
and Q-switched crystal, flexible adjustment of model parameters and
decrease of the laser size.
The paramerers of the Z-shape cavity:
       R 2  R 3  200mm     R1  R 4  

Half angle is 15o
       L1  10mm
       L 2  125mm           L 3  225mm

       L 4  60mm            L5  15mm
Fig. 2 the shape of the optical pulse when the repeated frequency is 5KHz
Experimental results:
When the pump power is 23W and the repeated
  frequency is 5KHz

 The max single puls energy output at
  1064nm is 0.74mJ
 The max peak power at 1064nm is 16.44kW
 The min pulse width is 35ns
Fig.3 the experimental setup of the LD-end-pumped CW Nd:YVO4
        all-solid-state inner-cavity frequency-doubled laser
Parameters :

            L11 = 15mm ;
           L12 = 125mm ;
            L 2 = 225mm ;
            L 3 = 115mm ;
               θ = 15 o。
The KTP cutting angle:     90   23 .5 o
                                o
   (a)
Fig. 4 the relationship of the output power at 532nm and
the input power at 1064nm, the max output is 4.44W and
        the light-light transfer efficiency is 19.06%
B: LD-side-pumped Nd:YAG all-solid-
state EO (Electro-Optic) Q-switched laser
                                                                           14mm



                                                  Nd:YAG side-pump
                               164mm

        KD*P crysral
                                   polarizer




                               102mm

   Platmirror: R=100%@1064nm                                 Plat mirror :T=40%@1064nm




             Fig. 5 the experimental setup of the LD-side-pumped
                   Nd:YAG all-solid-state EO Q-switched laser
                                               Single pulse energy 9.37mJ
                                               Pulse width 14.39ns
                                               Peak power 651.51kW




Fig.6 the shape of the optical pulse when the repeated frequency is 200Hz
                                            Side-pump system        10mm
         KD*P crystal           polarizer
                                                                             KTPcrystal




                                            Nd:YAG




                        164mm
                                                                                      Plat mirror
Plat miror                                                     Plat mirror            HR@1064nm,
R=100%@1064nm                                                  HR@808nm,              T=85%532nm
                                                               1064nmT=40%




   Fig. 7 the experimental setup of the LD-side-pumped Nd:YAG
          all-solid-state extra-cavity frequency-doubled laser
                                            Single pulse energy 0.82mJ
                                            Pulse width 8ns
                                            Peak power 90kW
                                            the light-light transfer
                                            efficiency is 17.98%




Fig. 8 the shape of the frequency-doubling optical pulse
 C. Random laser in laser dye-doped
     nano-composite PMMA film


1. Introduction
2. Characteristics and Recent Development
3. Our Experimental Results
   Introduction
   Lasers are now commonplace. They can be used in different
fields, for example, laser weapons in the military fields, laser
diagnosis and treatment in hospitals, bar-code scanners,
compact-disc players and display in daily life, especially high
power laser. Random laser is a kind of “thresholdless” laser
without an external cavity. According to the material composition,
random laser can be classified to three types. One is polymer
based laser including dye-doped PMMA nano-composites and
conducting polymer. The second is laser based on laser crystal
powders and semiconductor powders. The third is temperature-
tunable laser composite of laser dyes, liquid crystal and glass
powder. According to the difference of pumping source, they
include photoluminescence and electroluminescence.
Characteristics of random laser
   Spatial profiles of random laser emission intensity.
With the increase of pumping power, the light spot is
decreased. The light emission transfers from incoherent
Amplified Spontaneous Emission (ASE) to coherent laser.
Recent development

                                     They filled a porous glass
                                     structure with laser dye dissolved
                                     in a liquid crystal. Liquid crystals
                                     are chain-like molecules that
                                     align to a different degree
                                     depending on their temperature.
                                     As the degree of alignment
                                     changes, so does the diffusion
                                     coefficient of the overall structure.


Light emission: A temperature-tunable random laser, D Wiersma and S
Cavalieri 2001 Nature 414 708.
Action of a temperature-
tunable random laser
The phenomenon is caused by
the change of liquid crystal
phase with temperature.
Random laser used in disease diagnosis




  Random lasing in human tissues, Randal C. Polson and Z.
  Valy Vardenya, APPLIED PHYSICS LETTERS VOLUME 85,
  NUMBER 7 16 AUGUST 2004
FIG. 1. (Color) Random laser emission spectra of human
colon tissues infiltrated with a concentrated laser dye,
namely R6G. (a) Two typical random laser emission
spectra from a healthy, grossly uninvolved tissue (blue),
of which microscopic image is shown in (b). The narrow
spectral lines are in fact coherent laser emission modes
(Refs. 10 and 11. The inset shows schematically closed
random laser resonators formed due to scatters in the
gain medium. (c) and (d), same as in (a) and (b),
respectively, but for a malignant colon tissue. There are
more lines in the laser emission spectra in (c) (red) that
are due to more resonators in the tumor; these are
caused by the excess disorder that is apparent in (d).
Experimental results

  Yellow emission in PMMA films

   Material composition
   Rhodamine 590 +PMMA + TiO2 nanoparticles

  Pump Source
  The film was pumped at 532nm by the second
  harmonic of Nd:YAG laser at a 450 angle with
  respect to the normal direction of the film
Material preparation
Rhodamine 590 (Rhodamine 610) and TiO2 nano-
particles were mixed in 2ml of dichloromethane until the
dye was dissolved completely. Then 2ml 13wt% PMMA
dichloromethane solution was added to the above
mixture. The mixture was sonificated until a
homogeneous solution was formed. A PMMA film
containing Rhodamine 590 (Rhodamine 610) and TiO2
particles was formed by cell-casting of 1ml of the
solution.
SEM and SPM micrograph of PMMA nano-composite film
Particles and clusters are existed in film
      Experimental Results
                                   9000
                                   8500
                                   8000
                                   7500
       Emission Intensity (a.u.)



                                   7000
                                   6500
                                   6000
                                                                         a
                                   5500
                                   5000
                                   4500
                                   4000
                                   3500
                                   3000
                                                                         b
                                   2500
                                   2000
                                   1500
                                   1000
                                    500
                                      0
                                          540   560   580     600       620   640   660
                                                      Wavelength (nm)


Emission spectra of PMMA film doped with Rh590 and TiO2
particles with a pumping energy density (a) 1.9mJ/cm2, (b)
95mJ/cm2. a is scaled up by a factor of 10.
                           9000
                                                                                                                                                                             64
                                                                                                                                                                             60
                           8000
                                                                                                                                                                             56
                                        Emission Intensity(a.u.)




                           7000                                                                                                                                              52
                                                                                                                                                                             48
Emission Intensity(a.u.)




                                                                   1000


                           6000                                                                                                                                              44
                                                                                                                                                                             40




                                                                                                                                                             Linewidth(nm)
                                                                                                        2

                           5000                                                Pump Energy Density(mJ/cm )
                                                                                                                                                                             36
                                                                                                                                                                             32
                           4000                                                                                                                                              28
                                                                                                                                                                             24
                           3000
                                                                                                                                                                             20
                                                                                                                                                                             16
                           2000
                                                                                                                                                                             12
                           1000                                                                                                                                              8
                                                                                                                                                                             4
                             0                                                                                                                                               0
                                  -10                              0      10        20          30           40   50   60   70   80       90   100 110 120                        0   20     40    60    80   100   120   140   160
                                                                                                                                      2                                                                             2
                                                                                        Pump Energy Density(mJ/cm )                                                                        Pump Energy Density(mJ/cm )


                                                                (b)                                               (a)
Figure 2 Peak emission intensity (a) and line-width (b) of PMMA film
containing Rhodamine 590 and TiO2 particles plotted against pump energy
density. The inset of (a) is its log-log curve. The laser threshold is 5mJ/cm2.
   Red Emission in PMMA films
Material composition
Rhodamine 610 +PMMA + TiO2 nanoparticles

Pump Source
The pump condition is the same as yellow film.
Material preparation
The film preparation is almost the same as the yellow
film except for substituting Rhodamine 590 with
Rhdamine 610.
                                                                                                                    70
                        8000
                        7500                                                           2                            65
                                                                         0.6mJ/cm *10
                        7000                                                       2                                60
                                                                         52.8mJ/cm
                        6500                                                                                        55
                        6000
Peak Intensity (a.u.)




                                                                                                                    50
                        5500
                                                                                                                    45
                        5000




                                                                                                   Linewidth (nm)
                                                                                                                    40
                        4500                                                 a
                        4000                                                                                        35
                        3500                                                                                        30
                        3000                                                                                        25
                        2500
                                                                                                                    20
                        2000
                                                                                                                    15
                        1500                                       b
                        1000                                                                                        10
                        500                                                                                         5
                          0                                                                                         0
                                                                                                                         -10   0   10   20   30   40   50   60   70   80   90   100
                               540   560   580   600   620   640       660       680   700   720
                                                                                                                                                                  2
                                                 Wavelength (nm)                                                                        Pump Energy Density(mJ/cm )


Figure 4 (left) The emission spectra of PMMA film doped with Rh610 and TiO2
particles pumped at (a) 0.6mJ/cm2 (b) 52.8mJ/cm2 The amplitude of the
spectrum in a has been scaled up by a factor of 10 (right) The line-width Vs.
pump energy density. The laser threshold and line-width are 2mJ/cm2 and
4nm, respectively.
Optical fiber fabricated by the above nanocomposites.
They can be used in Random fiber laser with low
threshold or without threshold.

				
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