The basic components of a laser can be divided into three parts: pump source which provides the energy to invert the number of particles of working substances, working substances which has suitable structure of energy level and is able to invert the number of particles under the action of energy pump with electrons leaping down from higher energy levels and releasing the energy only in the form of photons) and resonant cavity. The properties of working substance exactly determines what wavelength of laser can be emitted.
The mainstay of laser at 808nm is semiconductor laser. The bandgap energy of semiconductor determines the wavelength of LD emission and 808nm is one of the common operating wavelengths. 808nm laser is also the semiconductor laser which has early start and is a sort of laser of in-depth study. The laser sources of 808nm laser includes aluminium-containing materials like nAlGaAs) and aluminium-free materials like GaAsP.
1064nm is a classical wavelength of solid state laser and the working material has YAG crystals in which aluminium ions can synergistically act on the Nd adulterated cations, producing a suitable spatial structure and energy band structure. Due to the action of excitation energy, Nd cations is in the excited state after excitation, resulting in radioactive jump which emits laser. The crystals of Nd: YAG have good stability and long working life.
The solid state laser with YVO4 crystal is suitable for LD pumping of 1064 nm wavelength.
Light in the infrared band can penetrate biological tissues relatively well and can have some applications in photo thermal therapy. For example, heparin(folic acid targeted modified nanoparticles), which is constructed with phorbol ester near infrared dye IR780 and whose maximum absorption wavelength is about 780 nm, emits at 807 nm. The temperature increased from 23℃ to 42℃ after 2min of laser irradiation (808 nm laser and 0.6 W/cm²power density) with the concentration of 10 g/mL. After administration at 1.4 mg/kg to tumor mice positively expressing folate receptor and irradiation with the 808 nm laser for 5 min (0.8 W/cm²) to the tumour sites of mice, a significant shrinkage of the tumors can be observed in the following days.
Other applications like infrared LIDAR, the current 905nm band has weak ability of weather interference and the penetration of rain and fog is also insufficient. The 1.5xum laser radiation is exactly at atmospheric window of 1.5~1.8um and the attenuation in the air is low. As 905nm is in the dangerous band for human eyes, the power must be limited to reduce its damage while 1550nm is in the safety band so it has applications in LIDAR.
On the whole, because some relevant wavelengths of laser process is more mature and the performance of price ratio is higher as well as these wavelengths of laser in different applications has shown excellent working performance, we can see the laser of these bands used in common applications.