Lumispot Technology Co., Ltd., based on years of research and development, successfully developed a small size and light weight pulsed laser with energy of 80mJ, repetition frequency of 20 Hz and human eye-safe wavelength of 1.57μm. This research result was achieved by increasing the conversation efficiency of KTP-OPO and optimizing the output of the pump source diode laser module. According to the test result, this laser meets the wide working temperature requirement from -45 ℃ to 65 ℃ with excellent performance, reaching the advanced level in China.
Pulsed Laser Rangefinder is a distance measuring instrument by the advantage of laser pulse directed to the target , with the merits of high-precision rangefinding ability, stronge anti-interference ability and compact structure. The product is widely used in engineering measurement and other fields. This pulsed laser rangefinding method is most widely used in the application of long distance measurement. In this long-distance rangefinder, it is more preferable to choose the solid-state laser with high energy and small beam scatter angle, using the Q-switching technology to output the nanosecond laser pulses.
The relevant trends of pulsed laser rangefinder are as follows:
(1) Human Eye-safe Laser Rangefinder:1.57um optical parametric oscillator is gradually replacing the position of the traditional 1.06um wavelength laser rangefinder in the majority of the rangefinding fields.
(2) Miniaturized Remote Laser Rangefinder with small-size and light-weight.
With the improvement of detection and imaging system performance, remote laser rangefinders capable of measuring small targets of 0.1m² over 20 km are required. Therefore, it is urgent to study the high-performance laser rangefinder.
In recent years, Lumispot Tech put the effort to the research, design, production and sale of the 1.57um wavelength eye-safe solid state laser with small beam scattering angle and high operating performance.
Recently, Lumispot Tech, designed an 1.57um eye-safe wavelength air cooled laser with high peak power and compact structure , resulting from the practical demand within the research of minization long-distance laser rangefinder,.After the experiment, this laser shows the wide application prospects, possessed excellent performace, strong environmental adaptability under the wide range of working temperature from - 40 to 65 degree celsius,
Through the following equation, with the fixed quantity of other reference, by improving the peak output power and decreasing the beam scattering angle, it can improve the measuring distance of the rangefinder. As the result, the 2 factors: the value of peak output power and small beam scattering angle compact structure laser with air-cooled function is the key part deciding the distance measurement ability of specific rangefinder.
The key part to realise the laser with human eye-safe wavelength is optical parametric oscillator (OPO) technique, including the option of non-linear crystal, phase matching method and OPO interiol structure design. The choice of Non-linear crystal depends on big non-linear coefficient, high damage ressiance threshold, stable chemical and physical properties and the mature growth techniques etc., phase matching should take precedence. Select a non-critical phase matching method with large acceptance angle and small departure angle; The OPO cavity structure should take into account efficiency and beam quality on the basis of ensuring reliability.the change curve of KTP-OPO output wavelength with phase matching angle, when the θ=90°, the signal light can exactly output the human eye safe laser. Therefore, the designed crystal is cut along one side, the angle matching used θ=90°，φ=0°, that is, the use of class matching method, when the crystal effective nonlinear coefficient is the largest and there is no dispersion effect.
Based on a comprehensive consideration of the above issue, combined with the development level of the current domestic laser technique and equipment, the optimization technical solution is : The OPO adopts a Class II non-critical phase-matching external cavity dual-cavity KTP-OPO design; the 2 KTP-OPOs are vertically incident in a tandem structure to improve conversion efficiency and laser reliability as shown in Figure 1 Above.
Pump source is the self-research and developed conductive cooled semiconductor laser array, with duty cycle of 2% at most, 100W peak power for single bar and the total working power of 12,000W. The right-angle prism, planar all-reflective mirror and polarizer form a folded polarization coupled output resonant cavity, and the right-angle prism and waveplate are rotated to obtain the desired 1064 nm laser coupling output. The Q modulation method is a pressurized active electro-optical Q modulation based on KDP crystal.
Figure 1 Two KTP crystals connected in series
In this equation, Prec is the smallest detectable work power;
Pout is the peak output value of work power;
D is the receiving optical system aperture;
t is the optical systm transmittance;
θ is the emittering beam scattering angle of the laser;
r is the reflection rate of the target;
A is the target equivalent cross-sectional area;
R is the largest measurement range;
σ is the Atmospheric absorption coefficient.
Figure 2 : The arc-shaped bar array module via self-development ,
with the YAG crystal rod in the middle.
The Figure 2 is the arc-shaped bar stacks, putting the YAG crystal rods as the laser medium inside of the module, with the concentration of 1%. To resolve the contradiction between the lateral laser movement and the symmetric distribution of the laser output, a symmetric distribution of the LD array at an angle of 120 degrees was used. The pump source is 1064nm wavelength, two 6000W curved array bar modules in series semiconductor tandem pumping. The output energy is 0-250mJ with a pulse width of about 10ns and a heavy frequency of 20Hz. a folded cavity is used, and the 1.57μm wavelength laser is output after a tandem KTP nonlinear crystal.
Graph 3 The dimensional drawing of 1.57um wavelength pulsed laser
Graph 4 :1.57um wavelength pulsed laser sample equipment
Graph 5: 1.57μm output
Graph 6: The conversion efficiency of the pump source
Adapting the laser energy measuremnt to measure the output power of 2 kinds of wavelength respectively. According to the graph shown below, the resut of energy value was the average value working under the 20Hz with 1 min working period. Among them, the energy generated by the 1.57um wavelenth laser has the consquent change with the relationship of 1064nm wavelength pump source energy. When the energy of the pump source equals to 220mJ, the output energy of he 1.57um wavelength laser is able to achieve 80mJ, with the conversion rate up to 35%. Since the OPO signal light is generated under the action of certain power density of fundamental frequency light, its threshold value is higher than the threshold value of 1064 nm fundamental frequency light, and its output energy increases rapidly after the pumping energy exceeds the OPO threshold value. The relationship between the OPO output energy and efficiency with the fundamental frequency light output energy is shown in the figure, from which it can be seen that the conversion efficiency of the OPO can reach up to 35%.
At last, a 1.57μm wavelength laser pulse output with energy greater than 80mJ and a laser pulse width of 8.5ns can be achieved. the divergence angle of the output laser beam through the laser beam expander is 0.3mrad. simulations and analysis show that the range measurement capability of a pulsed laser rangefinder using this laser can exceed 30km.
|
Wavelength |
1570±5nm |
|
Repetition Frequency |
20Hz |
|
Laser beam scattering angle (beam expansion) |
0.3-0.6mrad |
|
Pulse Width |
8.5ns |
|
Pulse Energy |
80mJ |
|
Continuous Working Hours |
5min |
|
Weight |
≤1.2kg |
|
Working Temperature |
-40℃~65℃ |
|
Storage Temperature |
-50℃~65℃ |
In addition to improving its own technology research and development investment, strengthening the construction of R&D team and perfecting the technology R&D innovation system, Lumispot Tech also actively cooperates with external research institutions in industry-university-research, and has established a good cooperation relationship with domestic famous industry experts. The core technology and key components have been developed independently, all key components have been developed and manufactured independently, and all devices have been localized. Bright Source Laser is still accelerating the pace of technology development and innovation, and will continue to introduce lower cost and more reliable human eye safety laser rangefinder modules to satisfy market demand.
Post time: Jun-21-2023