This article introduces dpss, including its advantages, development, technology and types.

The full name of DPSS in English is Diode Pump Solid State, that is, pumped solid-state laser. It is a new type of laser with the fastest development and wide application in the world in recent years. This type of laser uses a semiconductor laser with a fixed wavelength to replace the traditional krypton lamp or xenon lamp to pump the laser crystal, thus achieving a new development, which is called the second-generation laser.

The development of DPSSL is inseparable from the development of semiconductor lasers. In 1962, the first homojunction gallium arsenide semiconductor laser came out. In 1963, American Newman first proposed the idea of using semiconductor as the pump source of solid-state laser. But in the early days, due to the poor performance of diodes, it was still immature as a pump source for solid-state lasers. Until the concept of quantum well semiconductor laser was proposed in 1978, and the use of MOCVD technology and the emergence of strained quantum well lasers in the early 1980s, the development of LD has reached a new level. Since the 1990s, high-power LD and LD array technologies have gradually matured, thus greatly promoting the research of DPSSL. This paper focuses on diode-pumped solid-state lasers, first briefly introduces the development status of LD arrays, and then combines the various lasers that the author has contacted, starting from the design of diode-pumped heads, and exemplifies the technology of DPSSL devices that have appeared in recent years. characteristics and development status.

1. Long work time. The lifespan of traditional krypton or xenon lamps is only a few hundred hours, and the longest does not exceed 2000 hours. The lifespan of the diode laser used for pumping is as high as tens of thousands of hours, which greatly reduces the maintenance cost of the user.
2. Low power consumption. The conversion efficiency of the traditional lamp-pumped laser is only about 3%, and most of the energy emitted by the pump lamp is converted into heat energy, resulting in a great waste of energy. The LD used in DPSSL emits a fixed laser with a wavelength of 808 nm that is absorbed by the laser crystal, and the light-to-light conversion efficiency can be as high as 40% or more, which greatly reduces the operating cost.
3. Small size, easy to design miniaturization. A DPSSL laser is about 1/3 or even smaller than a traditional lamp-pumped laser, making it easy to carry.

1. End Pump Solid State Laser

The biggest advantage of the end-pumping method is that it is easy to obtain good beam quality and can realize high-brightness solid-state lasers. Therefore, attempts to end-face pumping have never stopped. In this system, an 8W semiconductor laser is used as the pump source. After output, it is shaped by a columnar prism group, and the beam divergence angle is compressed and focused before being input to the laser crystal. One end of the laser crystal near the pump source is coated with an 808nm antireflection coating and a 1064nm high reflection coating. The 808nm anti-reflection film minimizes the loss of the 808nm wavelength laser emitted by the pump source before entering the laser crystal, while the 1064nm high reflection film is combined with the output mirror coated with the 1064nm partial reflection film to form a resonant cavity, making the 1064nm The laser produces oscillation amplification and output. In this structure, the crystal mode activated by the pump beam is small, so it is generally used in applications with low power. For example, the purpose of ACI’s design of this laser is to use it in a 3W laser marking machine system. However, the advantage of the end pump is that the output laser mode is better, which is convenient to realize the TEM00 output. It is very practical in some occasions where the power requirement is not high and collimation is required. Such as laser ranging, marking of electronic components and so on.

2. Side Pump Solid State Laser

Researchers at Hughes Aerospace Laboratory achieved a high power output of 0.95KW by side-pumping a rod-shaped Yb:YAG crystal. This is the maximum power output obtained by pumping a single Yb:YAG with a semiconductor laser. The side pump solid-state laser head is composed of three diode pump modules in a circle to form a pump source, and each pump module is composed of three diode line arrays with microlenses. The average output power of each line array is 20W and the output wavelength is 808nm. The device uses glass tubes to cleverly design the pumping cavity and cooling channels. Most of the surface of the glass tube is coated with 808nm high-reflection film, and the remaining part is coated with three 808nm anti-reflection films at 120°, thus forming a pump cavity. The light emitted by the diode pump source is condensed into the three long and narrow areas coated with anti-reflection coatings through three pairs of beam shaping lenses, and then passes through the tube wall of the glass tube and is absorbed by the crystal. Since most of the glass tube is coated with a highly reflective film, after the pump light enters the pump cavity, it is reflected back and forth in the pump cavity until it is fully absorbed by the crystal, and a uniform gain distribution is formed on the cross section of the crystal. At the same time glass tube

It can also be used for refrigeration, and the heat generated by the cooling water passing through at a high speed is quickly taken away. The crystal adopts a composite structure Nd:YAG rod with an effective size of j3*63mm and a doping concentration of 1.5at.%. When the pump power is 180W, a laser output of 72W is obtained. The light-to-light conversion efficiency is as high as 40%.

3.  Thin Disc Pump

Thin-film laser is a new type of solid-state laser design that combines the advantages of end-pumping and side-pumping. It was first proposed by researchers at the Institute of Technical Physics of the German Aerospace Research Institute. Its basic concept is to use the fiber-coupled output semiconductor laser as the pump source to perform end-face pumping on a very thin crystal, so that the pump light passes through the crystal slice of several hundred microns for many times, and the distribution direction of the thermal gradient is consistent with that of the crystal. The propagation direction of the laser beam is the same. In the new pump design, a parabolic imaging mirror is used to replace the original 4 spherical imaging mirrors, which increases the number of times the pump light passes through the crystal from the original 8 to 16 times. Using the improved pump structure, at room temperature, pumping with a 24W CW laser and using a j3*0.2 Nd:YAG crystal flake, a 10W TEM00 continuous light output was obtained, and the optical efficiency was 41.7%. This thin-film laser has the characteristic of proportional power amplification. By cascading multiple thin-film crystals on the same heat sink, it is expected to obtain a high-efficiency kilowatt-class all-solid-state solid-state laser with a beam near the diffraction limit. The optical quality of the output of this laser is between that of end-pump and side-pump, and higher output power and better optical mode can be obtained. However, the design and debugging of such lasers are difficult, so they are not used by most laser companies.

4 Fiber Lasers

Fiber lasers have evolved from optical amplifiers in the optical communications industry in recent years. As soon as it was launched, it caused a shock in the industry. Its good optical quality, high output power, long life and maintenance-free characteristics have won the attention of many companies. Strictly speaking, it is a type of end-face pumping. The pump source of modern high-power fiber lasers is a high-power multimode diode implemented by a double cladding surrounding the single-mode core.

The idea of replacing the multimode emission output of solid-state lasers or broadband semiconductor laser diodes with a single-mode fiber laser was first proposed in the 1970s. In the simple double-clad fiber structure, an axial single-mode glass core is doped with the desired laser ions, such as rubidium, bait, ybium, thulium, etc. The core fiber is surrounded by an undoped glass cladding several times its diameter and has a lower refractive index. Next is the inner pump cladding, which is covered by an outer undoped glass cladding, which also has a lower index of refraction. In this fiber structure, the multimode diode pump light enters the pump cladding through the terminal face of a composite fiber, propagates through the fiber structure, periodically traverses the doped single-mode fiber core, and ends up in the core fiber. Produces a population inversion.

The IPG Laser Division (now a division of IPG Photonics) has developed a more advanced fully ruggedized side-pumped fiber laser. It consists of an active fiber with a polyhedral structure that can be freely spliced with other optical components or gain stages, thereby enabling pump light to be injected into the cladding from multiple points. In this way, a simple scaling control of the fiber output power becomes possible. Other side pumping techniques are V-groove coupling. In 1996, an industrial-quality, diffraction-limited 10-watt cladding-pumped fiber laser was brought to market by IPG Photonics. Similar lasers were soon introduced by Polaroid Corporation (Cambridge, MA), Spectra Diode Laboratories (now JDS Uniphase), and Spectra Physics.

Coupling the output power of multiple 100-watt fiber lasers can well boost the output power of fiber lasers to a higher level. For example, the output beams of seven 100-watt fiber lasers are transmitted over a distance of more than 30 meters through seven single-mode fibers, and then combined in a multi-core fiber beam coupler to output a beam with a diameter of 80 μm and a divergence angle of less than 40 mrad beam. This corresponds to a laser with an output beam parameter of <1.6 mm mrad; a coupled output power of 700 watts can act on the workpiece with an intense laser beam, up to more than 50 kilowatts per square centimeter. In comparison, a diode-pumped solid-state laser typically has beam parameters >10mm mrad, and its output power density is only 1/50 of that of a fiber laser. The 700-watt fiber laser measures 55 x 60 x 95 cm3 and weighs 120 kg. This form of laser can achieve very high power by lengthening the fiber according to the required power. However, its fatal weakness is that the single pulse energy is not high, which limits the application field of fiber lasers to a certain extent. At present, all countries in the world regard how to improve the single-pulse energy of fiber lasers as a key research and development topic.

This paper focuses on the technical characteristics of the laser head, the core component of several semiconductor-pumped solid-state lasers that have appeared in recent years, from the perspective of experimental devices and principles. High-power, high-brightness DPSSL has always been a frontier topic in the laser field at home and abroad. At present, there have been many reports of kilowatt-level DPSSL systems abroad, and Japan is also expected to achieve high-power all-solid-state lasers with an average output power of ≥10KW and an electro-optical efficiency of ≥20% and a laser head size of ≤0.05m3 in 2005. The development of DPSSL in China is relatively backward, but with the gradual maturity of high-power LD and LD array manufacturing technology in my country in recent years, DPSSL is bound to have a more vigorous development.