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.

200mmRR 32 41 RR

10mmL1 125mmL2 225mmL3

60mmL4 15mmL5

The paramerers of the Z-shape cavity：

Half angle is 15o

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 freq

uency 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

。o

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Parameters :

o90 o5.23The KTP cutting angle:

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%

(a)

B: LD-side-pumped Nd:YAG all-solid-state EO (Electro-Optic) Q-switched laser

polarizer

Nd ： YAG side-pump

KD*P crysral

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

102mm

14mm

164mm

Fig. 5 the experimental setup of the LD-side-pumped Nd:YAG all-solid-state EO Q-switched laser

Fig.6 the shape of the optical pulse when the repeated frequency is 200Hz

Single pulse energy 9.37mJPulse width 14.39nsPeak power 651.51kW

Nd:YAG

KD*P crystal polarizer

Side-pump system

KTPcrystal

Plat miror R=100%@1064nm

Plat mirrorHR@808nm ，1064nmT=40%

10mm

164mm

Plat mirrorHR@1064nm ，T=85%532nm

Fig. 7 the experimental setup of the LD-side-pumped Nd:YAG  all-solid-state extra-cavity frequency-doubled laser

Fig. 8 the shape of the frequency-doubling optical pulse

Single pulse energy 0.82mJPulse width 8nsPeak power 90kW the light-light transfer efficiency is 17.98%

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

Light emission: A temperature-tunable random laser, D Wiersma and S Cavalieri 2001 Nature 414 708.

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.

Action of a temperature-tunable random laser The phenomenon is caused by the change of liquid crystal phase with temperature.

Random lasing in human tissues, Randal C. Polson and Z. Valy Vardenya, APPLIED PHYSICS LETTERS VOLUME 85, NUMBER 7 16 AUGUST 2004

Random laser used in disease diagnosis

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-partic

les 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 c

ell-casting of 1ml of the solution.

SEM and SPM micrograph of PMMA nano-composite film

Particles and clusters are existed in film

Experimental Results

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particles with a pumping energy density (a) 1.9mJ/cm2, (b) 95mJ/cm2. a is scaled up by a factor of 10.

(a) (b)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.

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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.

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.

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Optical fiber fabricated by the above nanocomposites. They can be used in Random fiber laser with low threshold or without threshold.