The carbon dioxide laser

Decay of the 1 and 2 lower levels of the laser transitions are rapid down to the 2 level this is depopulated mostly by collisions with helium atoms in the CO2 N2 Fie gas mixture which is used. 

Lifetimes of upper and lower states are governed by collisions and that of the upper is always longer than that of the lower in the gas mixtures used. 

The energy input into a CO2 laser is in the form of an electrical discharge through the mixture of gases. The cavity may be sealed, in which case a little water vapour must be added in order to convert back to CO2 any CO which is formed. More commonly, longitudinal or, preferably, transverse gas flow through the cavity is used. The CO2 laser can operate in a CW or pulsed mode, with power up to 1 kW possible in the CW mode. 

The assignments of these levels was reversed in 1965. The new assignments are used here. 

Unless the cavity is tuned to a particular wavelength the vibration-rotation transition with the highest gain is the P-branch transition involving the rotational level which has the highest population in the 3 state. This is P(22), with J = 22 and J = 21, at normal laser temperatures. The reason why this P-branch line is so dominant is that thermal redistribution of rotational level populations is faster than the population depletion due to emission. 

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Diamond. M., Daniell, J., Martin, D., Feste, J., Vaughn, W. K. and McLaughlin, D. S., Tubal patency and pelvic adhesions at early second-look laparoscopy following intraabdominal use of the carbon dioxide laser initial report of the intraabdominal laser study group, Fert. Steril., 42, 717,1984. 

Sharply localized curing can be achieved with laser beams. The carbon dioxide laser, which has a total beam output of 100 W/cm at a wavelength of 10.6 pm, can be used for this purpose. 

A more dense coating can be obtained by a laser treatment. In the course of this treatment, the polymer coating is remelted. Several laser types have been tested, the most suitable laser is the carbon dioxide laser to get more compact coatings. The laser-treated coating shows an amorphous structure. However, no obvious chemical modification is observed after the flame spraying process and the laser treatment. ... 

The use of the DIAL method in the mid-infrared spectral region has arisen from the availability of the high-powered carbon dioxide laser and the wide range of species with absorption lines in the range 9-11 pm. However, the carbon dioxide laser cannot be tuned continuously across the spectrum so it is not possible to use a single carbon dioxide laser to measure all the species that have absorption lines in this region of the spectrum. Possible applications include ... 

Samples such as dichlorodifluoromethane, chlorotri-fluoromethane, and ethanol are separated by a conventional gas chromatograph column (Carbowax 20M) and are excited at the P32 line of the carbon dioxide laser (933cm ). The reported detection limit is an absorbance of 2.5 x 10 . ... 

M. Remade, G. Lawson, M. Nollevaux, and M. Delos, "Current state of scanning micromanipulator applications with the carbon dioxide laser," Ann. OtoL, Rhinol. LaryngoL, 117(4) 239-244, April 2008. 

A third common type of gas laser is the carbon dioxide (COj) laser, which produces infrared light at 10.6 micrometers ( xm). The carbon dioxide laser is the most efficient and powerful of all gas lasers producing high powers-up to 1000 watts (W). Such a beam can easily cut through steel and is used in welding, drilling, and cutting. 

The carbon dioxide laser has greater productivity than the excimer laser or the UVYAG laser when used to generate via holes larger than 60 /rni in diameter however, it cannot drill through copper foil directly. As a result, a black surface treatment is required on the thin copper foils before the laser operation. (See Fig. 63.6) Comparisons of the technical capabihties of these micro via processes of the laser systems are shown in Table 63.4. 

The excimer laser process, like the UV YAG laser system, minimizes the potential for thermal damage on very thin flying leads. The carbon dioxide laser generates a remarkable amount of heat. The beam power density of the laser must be controlled carefully in order to process 18-fjm copper with high-density flying leads narrower than 100 fjm wide. 

The carbon dioxide laser is the most efficient gas laser, with a wall-plug efficiency of up to 20%. It worlcs in the IR region aromid 10 pm. In numerous apphcations a non-tmied CO2 laser is used. However, from a spectroscopic point of view, the fact that it can be fine-tuned and continuously tuned at high gas pressures is very useful. In Fig. 3.30 a level diagram and a practical arrangement for a tuned CO2 laser are shown, together with a diagram of the available fines. The CO2 molecule has three fundamental modes of... 

The carbon dioxide laser can operate at several wavelengths, which have been measured accurately, and is, therefore, well suited to such measurements. The laser is switched rapidly between two of these wavelengths and the output signal obtained from a detector as one of the interferometer mirrors is moved is squared, low-pass Altered, and processed in a computer to obtain the phase difference. Distances up to 100 m can be measured with an accuracy of one part in 10. ... 

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