CN112945522B - A test method for cavity-free short-pulse polymer fiber random laser - Google Patents

Abstract

The invention discloses a test method for a cavity-free short-pulse polymer fiber random laser. A cylindrical polymer fiber random laser is used as a sample to be tested. A nanosecond pulse laser pumps the cavity-free polymer fiber random laser end face to establish a short-pulse random laser. laser, and evenly divide the random laser into two beams of light. The spectrometer tests one of the light signals to collect the spectral waveform, and the photodetector tests the other light signal to collect the time domain waveform. By testing the changes in the establishment of a random laser in a polymer fiber under different pump energies, the random laser spectrum and time domain information under the current pump energy are obtained in real time, and the establishment of a short pulse random laser is demonstrated from a time domain perspective, so that The narrowing of short pulses varies by an order of magnitude. The present invention can demonstrate the establishment of a short-pulse random laser inside a cavity-free polymer fiber and the laser mode mechanism, and will be of great significance in studying the internal dynamics of a polymer fiber random laser.

Description

A test method for cavity-free short-pulse polymer fiber random laser

Technical field

The invention relates to the technical field of optical fiber random laser testing methods, and in particular to a testing method for a cavity-less short pulse polymer optical fiber random laser.

Background technique

Random laser is a laser that does not require a traditional resonant cavity and obtains light amplification and multiple scattering feedback through a gain medium (such as laser crystal or amorphous powder) and a disordered scattering medium. The pump light and emitted light participate in multiple scattering. The process increases the residence time and interference probability of photons inside the structure, and allows the gain medium to provide sufficient amplification to compensate for the absorption and leakage of light through boundaries. Random lasers have low cost, simple structure, low threshold, good coherence, long life, and tunability and have been widely studied. There are many types of random lasers doped by different types and forms of media, among which polymer fiber random lasers have attracted much attention. V.R. Anand et al. used a 532-nanometer laser to pump a hollow polymer fiber doped with rhodamine B to obtain a temperature-tunable wavelength laser with a sensitivity of 0.09 nanometers/degrees Celsius. M.A. Illarramendi et al. tuned the luminescence properties of rhodamine 6G-doped gradient refractive index polymer fibers through the polarization angle of the pump light. These studies demonstrate that polymer fibers are stable and tunable, demonstrating the bright future of polymer fiber random lasers for use in sensors, optical switches, and full-field imaging.

The study of random laser time domain has always been a hot spot that has attracted widespread attention. The direct manifestation of random laser time domain is the time profile of photoluminescence. The essence of photoluminescence is the dynamic process of photons relaxing from the excited state to the ground state, including the interaction process between light and matter: linear fluorescence and nonlinear stimulated emission. E. Pecoraro et al. used a photomultiplier tube to collect the time emission characteristics of rhodamine-doped diurea hybrid powder, and found that the time distribution narrowed, showing a parallel behavior as a function of pump power density, and the effective emission line width was from 6 nanoseconds. It dropped to 400 picoseconds. The duration of the pulse is limited by the laser dye lifetime, which is reflected in the monoexponential behavior of the attenuation profile. X.Shi proposed a new method to determine the threshold based on time profile measurement. The delay time of establishing the laser and the rising edge time of the time domain were collected. As the pump power increased, both decreased super-linearly and showed two characteristics. The two inflection points correspond to the operating threshold and laser mode conversion respectively. This series of studies shows that the random laser time domain has good research potential and contributes to our understanding of the dynamics of random laser emission.

At present, there are no reports on the time domain research of polymer fiber random lasers, and the experimental demonstration of the establishment of short-pulse random lasers has always been discussed from the perspective of spectral intensity and wavelength changes. Therefore, the content of the present invention adopts a new test method to collect the time domain information of the cavity-free polymer fiber random laser, and demonstrates the establishment of short-pulse random laser from the perspective of the time domain. This invention will pave the way for future cavity-free random lasers. The preparation of short-pulse polymer fiber random lasers and the study of internal dynamics provide a new strategy.

Contents of the invention

The purpose of the present invention is to make up for the shortcomings of the existing technology and provide a test method for a cavity-free short-pulse polymer fiber random laser to obtain the spectrum of the polymer fiber random laser and test the time domain waveform of the current random laser in real time. The establishment of short-pulse random laser is demonstrated from the perspective of time domain.

The present invention is achieved through the following technical solutions:

A test method for a cavity-free short-pulse polymer fiber random laser, including the following steps:

(1). Use the prepared cylindrical polymer fiber random laser as the sample to be tested;

(2) Using a nanosecond pulse laser as the pump light source, the pump light is emitted to couple into one end of the sample to be measured. When passing through the fiber core, a random laser is formed under the combined action of the laser dye and nanoparticles, and the remaining pump light The mixed light with the random laser is emitted from the other end of the sample to be tested, a filter is used to filter out the remaining pump light, and a beam splitter is used to divide the random laser into two beams of light equally;

(3) Use the optical fiber probe of the fiber spectrometer to receive one of the random laser beams, and obtain the spectral information of the random laser by changing the pump laser intensity multiple times; use the photodetector probe to receive the other random laser beam, and convert the optical signal To transmit the electrical signal to the oscilloscope, the time domain information of the random laser is obtained by changing the pump laser intensity multiple times.

The polymer fiber random laser described in step (1) does not have an optical resonant cavity and generates short-pulse random laser with a pulse width in the range of 400 picoseconds to 8 nanoseconds by adjusting the pump energy.

In step (2), the pump laser emitted by the pump light source is sequentially aggregated through a set of Glan mirrors and convex lenses and then coupled into the sample to be measured. The two Glan mirrors of a set of Glan mirrors control the pump laser respectively. energy magnitude and polarization direction.

The beam splitter described in step (2) uses a 50:50 non-polarizing beam splitter to divide the random laser into two random laser beams in different directions on average and without any difference.

In step (3), one of the random laser beams is coupled into the fiber probe of the fiber spectrometer. The fiber spectrometer receives the optical signal and transmits it to the computer, obtains the current spectral information of the random laser, and adjusts the Glan lens group to change the energy intensity of the pump light. Thus, the random laser properties are changed, and the information about the spectrum changes with the pump intensity is statistically obtained.

In step (3), another random laser beam is coupled into the photodetector probe. The photodetector converts the optical signal into an electrical signal and transmits it to the oscilloscope. The oscilloscope simulates the collected voltage change to the random laser time domain change curve. When When adjusting the Glan mirror group to change the pump intensity to control the spectral changes, the time domain signal also changes at the same time, and the information of the time domain changes with the pump intensity is statistically calculated.

The advantage of the present invention is: in the present invention, the principle of establishing short-pulse random laser is to use a cavity-free polymer fiber random laser with laser dye and nanoparticles doped in the fiber core as the sample to be tested. Inside the polymer fiber core The irregularly distributed nanoparticles form a random structure that causes the pump light to scatter strongly and disorderly multiple times inside the fiber core, increasing the probability of light propagating in a loop and providing sufficient optical feedback for the formation of short-pulse random lasers. , and the laser dye provides a gain effect, causing the dye molecules to absorb photons and amplify the laser to create a short-pulse random laser;

Under the same pump energy intensity, the present invention uses a 50:50 non-polarizing beam splitter to evenly divide random laser light into two beams of light to collect spectra and time domain waveforms respectively; by testing the polymer optical fiber at different pump energies Establish the change of random laser under the condition, and use fiber spectrometer, photodetector and oscilloscope to collect random laser signals respectively. We can obtain the random laser spectrum and time domain information under the current pump energy in real time, thus for the short pulse random laser Establishment provides experimental demonstration;

This invention is the first disclosed polymer fiber random laser test method. It can demonstrate the establishment of short-pulse random lasers and laser mode mechanisms inside cavity-free polymer fibers. It will be important in studying the internal dynamics of polymer fiber random lasers. meaning.

Description of the drawings

Figure 1 is a device diagram of the polymer fiber random laser testing method in the present invention.

Figure 2 is a normalized time domain diagram of the random laser in the present invention under different pump energies.

Figure 3 is a half-height full width diagram after time domain fitting of the random laser in the present invention under different pump energies. The dotted line in the diagram is the threshold of the random laser of 40.79 microjoules.

Detailed ways

A test method for a cavity-free short-pulse polymer fiber random laser, including the following steps:

(1). Prepare a cylindrical polymer fiber random laser 1. The polymer fiber random laser 1 to be tested consists of two parts: a core and a cladding. The core is doped with laser dyes and nanoparticles. The core of the polymer fiber random laser 1 to be tested is doped with polysilsesquioxane nanoparticles and PM597 laser dye. The mass fraction of PM597 laser dye is 0.14wt.%, and the mass fraction of polysilsesquioxane nanoparticles is is 22.9wt.%. The cladding diameter is 696.42 microns, the core diameter is 26.78 microns, the length is 3 cm, and the threshold is 40.79 microjoules.

(2) As shown in the test device in Figure 1, a Q-switched Nd:YAG laser with an output wavelength of 532 nanometers, a pulse duration of 6 nanoseconds, a repetition frequency of 10 Hz, and a spot diameter of 100 microns is used as the pump light source 2, and the emission pump The pump light is coupled into one end of a 3 cm long polymer optical fiber through a convex lens 3 with a focal length of 10 cm, and is emitted from the other end of the optical fiber. At this time, it is a mixed light of the remaining pump light and the random laser, with a cut-off wavelength of 550 nm. The filter 4 filters out the remaining pump light and leaves only the random laser. A reflector 5 is used to change the path of the random laser, and the random laser is guided through the lens 6 to a piece with a side length of 30 mm and a beam splitting ratio of 50: 50 non-polarizing cubic beam splitter 7, the beam splitter 7 splits the random laser into two beams of light.

(3), 50% of the light is coupled to the micro spectrometer 8 (model QE65PRO, Ocean Optics, resolution 0.4 nm, integration time 100 milliseconds) by the optical fiber probe to measure the spectrum of the random laser. The remaining 50% of the light is emitted to the silicon photodetector 9 with a bandwidth of 2 gigahertz and a rise time of 150 picoseconds. The photoelectric effect occurs inside the photodetector 9 and converts the collected random laser signal into a voltage signal for transmission. Given an oscilloscope 10 with a bandwidth of 1 gigahertz, the time domain waveform of the random laser can be collected from the oscilloscope 10 . This method can simultaneously test the spectrum and time domain of random lasers by changing the pump laser intensity multiple times, greatly reducing testing errors.

In step (1), the prepared polymer fiber random laser 1 is different from traditional lasers in that it does not have an optical resonant cavity. By adjusting the pump energy, a short-pulse random laser with a pulse width in the range of 400 picoseconds to 8 nanoseconds can be generated. .

In step (2), the pump laser passes through a set of Glan mirrors 11 and is polymerized by the convex lens 3 before being coupled into the polymer fiber sample. The two Glan mirrors control the energy and polarization direction of the pump laser respectively.

In step (2), the mixed light of the remaining pump light and the random laser is emitted from the other end of the polymer optical fiber sample. The filter 4 filters out the remaining pump light and leaves only the random laser, using a 50:50 non-polarized type. The beam splitter 5 can divide the random laser light into two random laser beams in different directions evenly and without any difference.

In step (3), one of the random laser beams is coupled into the fiber probe of the fiber spectrometer. The spectrometer receives the optical signal and transmits it to the computer 12 to obtain the current spectral information of the random laser and adjust the Glan lens group 11 to change the energy intensity of the pump light. , thereby changing the random laser properties and statistically obtaining information on how the spectrum changes with the pump intensity.

In step (3), another random laser beam is coupled into the photodetector 9 probe. The photodetector 9 converts the optical signal into an electrical signal and transmits it to the oscilloscope 10. The oscilloscope 10 simulates the collected voltage changes to simulate the random laser time domain. Curve. When the Glan mirror group 11 is adjusted to change the pump intensity to regulate the spectral changes, the time domain signal also changes simultaneously, and the information of the time domain changes with the pump intensity is statistically calculated. The function of the beam splitter 7 is to simultaneously test the spectral information and time domain information of the same random laser beam at the same time and pump intensity.

Figure 2 is the normalized time domain diagram of the random laser to be tested under different pump energies. As the pump energy increases, the function of pulse duration and pump energy shortens significantly. When the pump light energy is 23 microjoules, the dye molecules absorb the energy, and the time signal begins to grow rapidly. The energy has not yet reached the threshold. The main emission mode is spontaneous amplified radiation, which is a wider fluorescence state. The right side of the time waveform corresponds to The dye molecules spontaneously decay relatively slowly, and the emission line width at this time is limited by the lifetime of PM597. When the energy increases to 38 microjoules, the time domain linewidth narrows from 6.46 nanoseconds at 23 microjoules to 2.46 nanoseconds, which is narrower than the width of the pump pulse of 6 nanoseconds, proving that a short-pulse random laser begins to be established inside the fiber. . When the pump energy is 50 microjoules, it exceeds the random laser threshold of 40.79 microjoules. The main emission mode inside the fiber is stimulated radiation, and a short-pulse random laser is completely established.

Figure 3 shows the relationship between the emission line width of the time profile and the pump energy calculated by Gaussian fitting of the normalized time distribution. The dotted line in the figure represents the threshold of 40.79 microjoules. When the threshold has not been reached, the relaxation process inside the sample has begun to establish stimulated emission, and there is a transition zone where stimulated emission and spontaneous amplified emission are mixed. When the energy is much higher than the threshold, stimulated emission is the main mode. At 50 microjoules, the emission linewidth is narrowed from 7.15 nanoseconds at 18 microjoules to 0.69 nanoseconds, reaching an order of magnitude change, which proves the establishment of short pulses. , the broad tail of the temporal distribution of photoluminescence is completely suppressed and only the narrow peak of gain survives.

The invention discloses a cavity-free short-pulse polymer optical fiber random laser and a testing method. By testing the polymer optical fiber under different pump energies, the changes of the short-pulse random laser are established, and the optical fiber spectrometer, photoelectric detector and oscilloscope are used to collect light respectively. signal, we can obtain the spectrum and time domain information of the short-pulse random laser under the current pump energy in real time, and demonstrate the establishment of the short-pulse random laser. This test method is also applicable to other types of random lasers, such as solution, Powder, gel, film, electrospinning, etc. This invention is the first disclosed polymer fiber random laser test method. It can demonstrate the establishment of short-pulse random lasers and laser mode mechanisms inside cavity-free polymer fibers. It will be important in studying the internal dynamics of polymer fiber random lasers. meaning.

Claims (1)

1. A testing method of a cavity-free short pulse polymer fiber random laser is characterized in that: the method comprises the following steps:

(1) Taking the prepared cylindrical polymer fiber random laser as a sample to be measured;

(2) A nanosecond pulse laser is used as a pumping light source, pumping light is emitted to be coupled into one end of a sample to be detected, random laser is formed under the combined action of laser dye and nano particles when the pumping light passes through a fiber core, mixed light of the residual pumping light and the random laser is emitted from the other end of the sample to be detected, the residual pumping light is filtered by a filter, and the random laser is equally divided into two beams by a beam splitter;

(3) Receiving one beam of random laser by using an optical fiber probe of an optical fiber spectrometer, and obtaining spectrum information of the random laser by changing the intensity of the pumping laser for a plurality of times; receiving another beam of random laser by adopting a photoelectric detector probe, converting an optical signal into an electric signal, transmitting the electric signal to an oscilloscope, and obtaining time domain information of the random laser by changing the intensity of pumping laser for a plurality of times;

the polymer fiber random laser in the step (1) has no optical resonant cavity, and short pulse random laser with the pulse width in the range of 400 picoseconds to 8 nanoseconds is generated by adjusting pumping energy;

in the step (2), the pump laser emitted by the pump light source is coupled into the sample to be tested after being polymerized through a group of gram mirror groups and convex lenses, and the two gram mirrors of the group of gram mirror groups respectively control the energy and the polarization direction of the pump laser;

the beam splitter in the step (2) adopts a 50:50 unpolarized beam splitter to split random laser evenly and indiscriminately into two random lasers in different directions;

in the step (3), one of the random lasers is coupled into an optical fiber probe of an optical fiber spectrometer, the optical fiber spectrometer receives an optical signal and transmits the optical signal to a computer to obtain the current spectrum information of the random lasers, the energy intensity of pump light is changed by adjusting a gram mirror group, so that the property of the random lasers is changed, and the information of the spectrum changing along with the pump intensity is counted;

in the step (3), another beam of random laser is coupled into a photoelectric detector probe, the photoelectric detector converts an optical signal into an electric signal and transmits the electric signal to an oscilloscope, the oscilloscope simulates the acquired voltage change to a change curve of a random laser time domain, when the adjusting gram mirror group changes the pumping intensity to regulate and control the spectrum change, the time domain signal is also changed simultaneously, and the information of the time domain changing along with the pumping intensity is counted.