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Model GL-3300 Nitrogen Laser

Also applicable to the PL-2300

CONTENTS

GENERAL

Dimensions and Controls

A.C. line cord connector. Fuse holder. Nitrogen input. The input pressure is displayed on the gauge marked G2 above the input. Main power key switch. The key cannot be removed when the laser is operating. POWER indicator. Illuminated when laser system power is on. LASER ON indicator. Illuminated 10 seconds after system power is turned on. Trigger mode selector. Selects either internal trigger operation or external trigger source. Rep rate control. Controls the rep rate when the trigger mode is set to internal. Trigger button. When trigger mode is set to external, a single laser pulse is emitted when this button is pressed. When trigger mode is set to internal, laser pulses are momentarily interrupted when this button is pressed. Trigger in connector. BNC connector provides input for external trigger source. Trigger pulse must be >3 volts and >100 nanoseconds. H.V. adjust control. Controls the voltage delivered to the laser head. The voltage applied is displayed on the meter above the control. Gas purge button. While this button is depressed, the system is purged with fresh nitrogen. Sync out connector. BNC connector provides a 1.5 microsecond wide, 24 V pulse, 1 microsecond before the laser fires. Remote shorting connector. This connector must be installed for the system to operate. Gas flow control. Provides fine adjustment of the gas flow to the laser channel. G1 adjust control. Sets the gas pressure within the trigger spark gap. The pressure is displayed on the gauge marked G1 above the control. Shutter. Opens and closes the laser output aperture. The aperture is opened and closed using the sliding shutter. It is open when the slider is pushed toward the body of the laser, and closed when it is pulled out.

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Warning Labels

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OPERATION

Initial Setup

1. Connect the N₂supply and set the pressures as indicated on the rear panel gauges.

2. Close the shutter.

3. Select external trigger mode.

4. Turn the key switch on (the power indicator will light).

5. Press and hold the gas purge button for 3 or 4 seconds to flush the system with fresh N₂.

6. After a 10 second safety delay, the laser on indicator will light.

7. Refer to your Quality Control Report and the following section for the proper H.V., gas flow and rep rate control settings to obtain the expected output.

8. Switch to internal trigger mode or apply an external trigger signal and lasing will commence.

9. Open the shutter. Output may be monitored on an energy meter or observed on a fluorescent card.

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Operation

Reference settings for normal operation are listed in your Quality Control Report at the front of this manual. The appropriate settings may need to be adjusted over time due to normal component wear, readjustment, etc. The spark gaps will operate in a range of +/-20% of rated pressure, so it is possible to compensate for some wear of the electrodes by lowering the pressure slightly.

The gas flow through the laser channel is a critical operating parameter, and must be carefully adjusted to obtain full laser energy output. Also, different rep rates will require different flow rates. For this reason, a micrometer is used for fine adjustment of the gas flow.

The scale on the barrel of the gas flow micrometer has four divisions per unit. The rotating knob has 25 divisions, and one full rotation is equal to one division on the barrel. Thus, 4 full rotations is equivalent to 1 full unit on the barrel scale.

NOTE: If you are familiar with the use of a micrometer, you will note that gas flow readings are equivalent to inches; for example, a gas flow reading of 16 is equivalent to 0.016 inches. Since the micrometer is being used for gas flow and not distance, we omit the decimal point from the readings.

Gas flow is best optimized by using an energy meter. However, the sound of the discharge is also a good indicator; too little or too much gas will produce a much sharper sound, and the output energy will be lower or less stable. Purging the system with fresh N₂ occasionally will help prevent misfires by flushing the spark gaps and removing discharge by-products.

The rep rate of the GL-3300 is from single-shot (in external trigger mode) to 20 Hz. Note that the internal mode rep rate control is not linear. In the control's full counter-clockwise position, the rate is approximately 0.6 Hz. In the full clockwise position, the rate is 20 Hz. When the indicator is in the vertical position, the rate is approximately 6 Hz.

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SERVICE

Maintenance Schedule

Optimum performance requires regular maintenance. The maintenance requirements of the GL-3300 are minimal and relatively simple, and only involve the cleaning of components subject to gas impurity deposition. These components include the two spark gaps, the laser channel, and the laser mirror. Gas impurity deposition degrades performance; cleaning these components will bring your laser back to original operating specifications.

The frequency of maintenance is dependent on the purity of the nitrogen gas and how many shots the laser has been fired. Lower rep rates require less frequent cleaning of the components. The following schedule is a general guide to determine when the laser components should be cleaned. (The recommendations are based on the assumption that lab grade nitrogen is used.) However, the performance of your laser should be used as the primary determinant for when cleaning is necessary.

Cleaning interval for absolute number of shots or continuous operation @ 5 Hz, 20 hr/week

Spark Gaps: 2-10 million shots or 5-28 weeks

Laser Channel & Mirror: 6-30 million shots or 15-84 weeks

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Spark Gaps

The GL-3300 uses two spark gaps to trigger the lasing process. The first spark gap (SG1) initiates the voltage multiplication process which develops across the two laser electrodes. One of these electrodes is in series with the second and larger spark gap (SG2), which acts as a breakdown gap. It quickly releases the potential from one laser electrode, thus creating the breakdown across the laser channel that results in excitation of the nitrogen gas. Both spark gaps use nitrogen gas as their active medium.

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Cleaning and Adjusting SG1

1. Remove the AC cord from the wall plug and also from the back panel.

2. Disconnect the N₂ gas supply.

3. Open the lid. There are ten screws which hold it shut. It is hinged at the back. After removing the screws, lift the lid up and back.

4. Remove the RFI shield surrounding the laser assembly. Remove the four screws holding it in place and lift it straight up.
   
   

5. Disassemble SG1. First, remove the white cap, which is connected to the red wire, from the spark gap trigger terminal. Then remove the four long screws holding the trigger housing and main housing to the bracket. Remove the trigger and main housing assembly.

6. Clean the interior of the spark gap with methanol and cotton swabs.

7. Check the adjustable electrode tip and adjust as necessary.

8. Reassemble SG1.

9. Replace the white cap on the trigger terminal.

10. Replace the RFI shield and secure the laser housing lid.

During normal operation, the adjustable electrode will wear down over time. This increases the electrode gap, which can adversely affect laser performance. To compensate for this normal wear, the adjustable electrode must be moved.

With SG1 disassembled, measure the distance from the electrode tip to the bracket. If it is less than 20 mm, the tip has worn and must be adjusted in order to maintain the factory setting of 2 mm. Loosen the lock nut and rotate the adjustable electrode holder, which is threaded into the bracket, until the tip-to-bracket distance is 20 mm.

The adjustable electrode will eventually wear to the point that it must be replaced. Contact PTI to obtain a replacement.

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Cleaning and Adjusting SG2

1. Remove the AC cord from the wall plug and also from the back panel.

2. Disconnect the N₂ gas supply.

3. Open the lid. There are ten screws which hold it shut. It is hinged at the back. After removing the screws, lift the lid up and back.

4. Remove the RFI shield surrounding the laser assembly. Remove the four screws holding it in place and lift it straight up.
   
   

5. Remove the four mounting screws which hold SG2 to the laser head.

6. Disassemble SG2 by removing the six screws holding the insulator to the main housing.

7. Do not clean the interior of the spark gap housing. The surfaces of the electrodes will normally darken in time as deposits are left on them. Only when they are excessively blackened do they require cleaning. Use emery cloth or a cleaning pad (such as Scotchbrite) to restore the shiny finish.

8. Reassemble SG2.

9. Adjust the electrode gap.

10. Remount SG2 to the bracket.

11. Replace the RFI shield and secure the laser housing lid.

During normal operation, the fixed electrode will wear down over time. This increases the electrode gap, which can adversely affect laser performance. To compensate for this normal wear, the adjustable electrode must be moved.

The factory setting is 3.5 mm. Screw the adjustable electrode in until it contacts the fixed electrode, then back it out 2.25 revolutions (1 revolution equals 1.6 mm). The electrode gap is set such that the laser fires between 15 and 17 KV. If your laser is not firing within this range, SG2 should be re-adjusted in, to lower the firing voltage, or out, to raise the firing voltage. If the laser is not performing satisfactorily after adjusting SG2, the laser channel and mirror should be inspected.

The fixed electrode will eventually wear to the point that it must be replaced. Contact PTI to obtain a replacement.

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Cleaning and Adjusting Laser Channel and Mirror

NOTE: Be sure you have a channel spacer before disassembling the laser head.

1. Remove the AC cord from the wall plug and also from the back panel.

2. Disconnect the N₂ gas supply.

3. Open the lid. There are ten screws which hold it shut. It is hinged at the back. After removing the screws, lift the lid up and back.

4. Remove the RFI shield surrounding the laser assembly. Remove the four screws holding it in place and lift it straight up.
   
   

5. Loosen the four plastic locking screws on the top of the laser head.

6. Pull out the high voltage connector located next to SG2.

7. Remove the six knurled nuts on the front of the laser electrode assembly and slide the assembly out.

8. Look through the aperture down the laser channel to inspect the mirror. If necessary, reach through the opening left by the electrode assembly and carefully clean the mirror with methanol.

9. To inspect and clean the laser channel, disassemble the removed electrode assembly. Remove the 2 plastic nuts and 4 slot screws holding the top transmission board to the assembly.

10. Lift the top transmission board off the assembly and clean the board and electrodes with methanol. Inspect the transmission board for black carbon tracks. These are a result of H.V. arcing and an indicator that the board may need replacement.

11. Realign the electrodes by reassembling the transmission boards without tightening the 2 plastic nuts and the 4 slot screws. Slide the spacer into the channel and adjust the large electrode such that the spacer is snug between the two electrodes along the entire length of the laser channel. (Note that the small electrode remains fixed.) Tighten the 2 plastic nuts and 4 slot screws.

12. Reassemble the laser head. Reconnect the H.V. line next to SG2.

13. Replace the RFI shield and secure the laser housing lid.

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Factory Service

Photon Technology International has designed the GL-3300 to provide years of dependable operation. The maintenance requirements of the GL-3300 are the simplest and least frequent of any nitrogen laser on the market. If after routine service the unit is not performing to your satisfaction, do not hesitate to call PTI for assistance. Most problems can be resolved over the phone.

In the rare instance your laser requires more than routine service, replacement parts and service support can usually be obtained by phone. We will need a purchase order for any replacement parts you require.

It is extremely rare that a laser or any of its components must be shipped back to PTI for service. However, if such service is required, you must obtain an R.A. (Return Authorization) number from PTI before shipment. No items will be accepted at the plant without an R.A. number.

We listen to our customers. While we feel that we have developed the most advanced nitrogen laser available, we are open to your suggestions. Please feel free to contact PTI.

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