Stability and Tuning with -S models where innovation never stops Achieving Stability without Breaking Your Budget
Stabilized lasers from Access Laser Company are made from Invar or other materials with high thermal mechanical stability. They also employ a feedback control system regulating the temperature of the laser resonator.
Bad news becomes good news Typical CO2 lasers line hop, from one wavelength to another, causing instability in spectrum and power. Reason: the length of the laser cavity drifts constantly under normal ambient conditions. Solution: Control the drift and we will control wavelength and achieve power stability.
How it works: Gratingless tuned Take advantage of the interaction between the molecular line spectrum and resonator modes by actively controlling the cavity length of the laser. Tune into single wavelength and stay. Method of tuning: Micrometer Temperature Piezo actuator
Spectral Distribution: Gratingless tunable Laser resonators are tightly controlled to force the laser to stay in the desired wavelength 10.2-10.7 μm or 10.7-11.2 μm ( 13 CO2)
Warming Up To Stability When the laser is first turned on it heats up. As a result the length of the cavity expands, and the laser goes through a sequence of lines before it is stabilized. This is the warm-up process, which typically takes 30-40 minutes.
Features Common to All -S Models All S model lasers can operate in single longitudinal mode and single transverse mode All S model lasers can operate in a single line You can minimize wavelength and power instability by tuning to the middle of the temperature range for a specific line. The more lines an S model laser can achieve the less temperature range each line has. Lines with a wide range of temperature are easier to achieve and are more stable, and vise versa.
Power & Spectrum Considerations to fit your application The smaller the laser the lower the power. The L3S is the shortest with 400mw of output power, and the L20S is the biggest at 20 watts. The smaller the laser, the more lines you ll have (you should notice this trend in the following pages). L3S has 12-17 lines typically, while L20S has 3-6. It is not practical to stay on one spectral line that has a very narrow range of temperature. Typical applications for S model lasers require one stable line around center of the wavelength band (P20 or R20). -S models offer best spectral purity and frequency stability when water cooled with a good chiller. For L4SL the measured line width is less than 100kHz. Frequency drift is less than 5MHz/min. Line Tracker is an option available for all S models, which improves power stability to ±1%, and enhances frequency stability.
Wavelength table of a typical model L3S, 400 mw laser, 14 lines.
Wavelength table of a typical model L4S, 1 W laser, 9 lines.
Wavelength table of a typical model MeritS, 8 W laser, 6 lines.
Wavelength table of a typical model L20-S, 20 W laser, 4 lines
The Line Table The line table, which goes with most S lasers is only for reference. In practice you may not achieve the desired line at the given temperature. This is because this table is recorded during ramp up of laser temperature after turn-on. Once the laser stabilizes it temperature range is shifted. The customer, if desire a particular wavelength, will need to find out exactly where that line is in his/her own ambient working environment, by experiment. If the laser is equipped with piezo actuator, then the table is obtained with the piezo set at a single ramp up when the laser is stabilized at a certain room temperature. The most important, and accurate information from a line table is the relative range of spectral lines. The wider the range the more stable the laser can be operating on a line. The range can be temperature or piezo voltage, depending on the specific laser model and options. Another piece of highly useful information is the sequence of spectral lines. Most spectral lines will appear in the sequence as recorded in rising temperature or piezo voltage.
Example of Using Line Table Looking at the line table of MeritS on Page 11, we find that 10P20 have the widest range of temperature from 82.3 to 87.5 F. Therefore we chose this line. Suppose by setting the laser body temperature at 84.9 degrees, which should be the middle of the range for 10P20 from the line table, we actually achieved 10P22. The line table shows that 10P22 appears at a lower temperature than 10P20. Therefore we increase the temperature setting to go for 10P20. Once the laser operates in one single wavelength its power is most stable. If the laser operates in a few lines at the same time it can negatively impact its power stability, in addition to compromised spectral purity.
Pick the Right Tool for Your Work Do you need linear polarization? L20S is by default linearly polarized in the horizontal direction. Linearly polarization is not default in other models, but can be added to L4S and MeritS Do you want to achieve even better stability? Consider Line Tracker, which provides closed loop feedback. Feel free to email us at sales@accesslaser.com, or call 425-582-8674.