Laser Material Processing Division

2 kW RF-excited FAF CO2 Laser

A compact 2.0 kW RF-excited fast axial flow (FAF) continuous wave (CW) CO₂ laser having good beam quality has been indigenously developed. The operating wavelength is 10.6µm. The RF-FAF Laser works at an efficiency of 17% at 1.5 kW level. It offers stable output power (±1.5% at 1 kW) and good beam quality suitable for high quality material processing studies.

Excitation:

The CO₂ laser, molecular gas laser in the IR region, here, is excited by electrical discharge. The gaseous active medium composed of the mixture, CO₂: N₂: He = 4:26:70, flowing at ~120m/s through eight quartz glass tubes of 20mm ID is pumped by a radio frequency electric voltage applied through a set of parallel profiled external Al electrodes placed transversely to the axial gas flow. The excitation of FAF CW CO₂ laser gas is achieved through a capacitively coupled RF discharge (CCRF) at 13.56 MHz. This type of excitation provides clean and efficient discharge for laser excitation. The RF power is generated by a water-cooled triode based Hartley power oscillator operating in Class C mode and is coupled to the impedance matching network through a 50W flexible coaxial cable. The discharge load impedance is matched to 50W using L-C network. Typically 9-10kW of RF power is used to excite gas mixture in 8 parallel discharge tubes as shown in the photograph. The laser power is controlled through gating of RF power by duty cycle variation from 10%-80% in the frequency range 100Hz-20kHz.

Construction:

The RF-FAF CO₂ Laser is based on heat removal by convective gas flow. In this laser it is realized through a high speed radial blower to circulate the gas mixture through a flow loop comprising quartz discharge tubes, gas mixing blocks, heat exchangers and flow separators. The flow loop is designed for symmetrical distribution of total available volumetric flow of gas mixture through the eight discharge tubes connected in parallel.   

Optical resonator:

 The laser employs plane-concave stable resonator configuration to provide feedback and extract useful laser output for material processing. It is realized using plane ZnSe output coupler/partially reflecting mirror and a curved total reflecting metal mirror. The output laser beam is circular with 17mm diameter and consists of TEM₀₀ and TEM₀₁* modes giving M²~3.

Applications:

Suitable for quality material processing studies viz., laser cutting of sheet metal, plastics & polymers, gas-phase nano-particle synthesis, high power novel optical beam generation (Super-Gaussian), EUV generation for HVM of chips at 13.5nm and research studies.

RF excited Fast Axial Flow (FAF) CW CO2 Laser

CCRF discharge