SECTION 1: STARTING 1.1 UNPACKING AND INSPECTION Upon receipt of the laser system, inspect the shipping containers for gross external damage. Unpack the unit and inspect for internal damage. If any damage is found, immediately notify the shipper and Lightwave Electronics. The 126-MOPA is shipped in one crate and two separate boxes that contain the following: Crate has Box with power supply Box with Chiller has 126-MOPA head Power supply Chiller with controller DB25 head control cable Power cable 20-A power cable Diode power umbilical cable Chiller control RS-232 Chiller manual 9-pin temperature sense cable Null modem adapter Master osc. umbilical cable Keys Master osc. DC power cord Microlock driver 2 insulated hoses MOPA and 126 manual 2 draining hoses Performance data sheet Test report When you receive the laser system, first turn the crated container and the two boxes upright as indicated by labels if it has been delivered improperly oriented. Retain the shipping cartons and packing material. If a component of the 126-MOPA system needs repair, the specially designed containers will ensure safe shipment of the unit to Lightwave Electronics. This manual is composed of chapters on: (1) Starting (unpacking and safety), (2) System Setup, (3) Basic Operation, (4) Power Supply and Electronic Interfaces, and (5) Service. There are appendices that have: (1) Pictures of the Laser System, (2) Performance Specifications, and (3) Packing Lists. Laser Head 1.2 PRODUCT OVERVIEW Lightwave Electronics 126-MOPA is a diode-pumped Nd:YAG master oscillator (MO) power amplifier (PA) system. The schematics of the laser head are depicted in Fig. 1-1. The MO is a Lightwave Electronics diode-pumped model 126 laser which produces narrow linewidth, frequency-stable, single-axial-mode output at a Nd:YAG wavelength of 1064 nm. At the heart of the model 126 laser is a patented (US patent 4579793) 5
monolithic, traveling-wave ring resonator, referred to as the NPRO (Non-Planar Ring Oscillator). Details about the model 126 laser can be found in the 126 users manual which is included in the 126-MOPA package. The PA amplifies the output of the 126 laser in a double-pass configuration. The PA module includes laser diodes that reliably, compactly, and efficiently pump the Nd:YAG laser gain medium, using Lightwave Electronics Direct-Coupled Pump (DCP ) technology. The PA contains a retro-reflecting mirror that allows for double-passing the gain medium. The laser output is separated from the input by utilizing the non-reciprocity of one of the two Faraday rotators that are part of the MO-to-PA coupling optics. There are two outputs from the MOPA head, a high-power (> 10 W) main beam and a low-power (approximately 50 mw) beam which represents a sample of the main beam. The sample beam is a transmission of the main beam through a leakage mirror. The beam sample can be used conveniently for power monitoring or other measurement purposes without affecting the main high-power beam. The laser head also contains two photo-detectors for monitoring the 126-MO output (= PA input) and the PA output. The optical signals to the detectors are provided by a transmission of the PA input and output beams through leakage mirrors at the PA input and output. As described in Section 4 of this manual the photo-detector signals can be monitored on the power supply in normal display mode and electrical signals are accessible through the 64-pin connector on the rear panel of the power supply. The laser head also contains an electronic memory chip that carries information on the PA within the laser head such as its proper operating current, operating temperature, and the accumulated hours of operation of the PA. In addition the laser head contains electronics which provide the appropriate drivers for the 126-MO diode current, the 126- MO diode thermo-electric cooler (TEC), NPRO crystal TEC and other controls. Consequently, laser heads are interchangeable with different power supplies or chillers. The laser head also allows for a slow and a fast laser frequency actuation and a MO current adjust (see 126 users manual) via 3 LEMO connectors. Before using the 3 inputs, jumpers JPZT1, JPZT2, JCM1 and JSL1 have to be removed. As will be described in Section 4.2, with the jumpers in place, frequency control and current adjust can also be achieved via an external 64-PIN connector at the back panel of the power supply. Appendix A presents pictures of the MOPA head, its inside and other components of the 126-MOPA system. The entire MOPA head is built on a 2 x 2 ft. breadboard with sealed holes and 4 or 5 Newport Microlocks for mounting onto an optical table or any other platform. Chiller The chiller cools the laser head with temperature-regulated water. Insulated water lines connect the chiller to the laser head. The chiller uses a CFC-free refrigerant loop to cool the water and exhausts the heat to the room air by a fan and radiator. As described in section 4 of this manual, the chiller can be locally controlled by its own micro-controller or remotely controller via the power supply through an RS-232 interface. Note that supplying the chiller with electricity requires a circuit rated for at least 20 A including a 6
special high current wall socket! A separate chiller manual provided by the chiller manufacturer is shipped with the 126-MOPA system. Power Supply The user controls the laser exclusively through the power supply, either directly via the manual controls on the front panel or externally via a computer that is connected to the 64-pin connector on the back of the power supply. The power supply includes electronics to drive the 126-MO and the PA. Parameters that can be controlled or monitored are described in Section 3 of this manual. A fan integral to the power supply cools the power supply's drive electronics. Low-Power Beam Sample High-Power Main Output Beam Coupling & Separation Retro- Reflector Power Amplifier Model 126 Master Oscillator Figure 1-1. Schematics of the laser head with the 126-MO, the coupling optics and the PA. General Background An excellent reference on the practical aspects of solid-state lasers is W. Koechner, Solid-State Lasers, Springer-Verlag, Berlin, 1992. An excellent reference on laser theory including laser modes is A. E. Siegman, Lasers, University Science Books, Mill Valley, 1986. We also recommend the following review article on the founding work in diode-laser-pumped lasers: T. Y. Fan and R. L. Byer, "Diode laser-pumped solid-state lasers," IEEE Journal of Quantum Electronics, Volume 24, page 895 (1988). 7
1.3 LASER SAFETY 1.3.1 Explanation of Terms The cautions and warnings used throughout this manual are explained below. WARNING: Warnings describe situations or equipment that can injure or be fatal to people. Mechanical damage may also result. CAUTION: Cautions describe situations or equipment hazardous primarily to equipment. 1.3.2 Safety Summary The 126-MOPA diode-pumped laser is a Class IV laser as defined by the Federal Register 21 CFR 1040.10 Laser Safety Standard. The Standard requires that certain performance features and laser safety labels be provided on the product. Photographs of the warning labels in place on the laser are shown in Section 1.3.4. The American National Standards Institute publishes a laser safety standard for users entitled American National Standard for the Safe Use of Lasers (ANSI Z136.1). Lightwave Electronics strongly recommends that laser users obtain and follow the procedures described in this ANSI standard. Copies may be obtained from: American National Standards Institute Inc. Laser Institute of America 1430 Broadway or 2424 Research Parkway New York, NY 10018 Orlando, FL 32826 WARNING: WARNING: WARNING: Avoid direct or indirect eye exposure. Direct exposure will result in permanent eye damage. Indirect exposure (viewing a diffuse reflection of the laser beam scattering off a surface such as ceramic or white paper) may result in permanent eye damage. Avoid direct skin exposure to the laser beam. Skin exposure will result in skin and flesh burns. The aperture that can emit laser energy in excess of levels that are considered safe is identified with the appropriate aperture label shown in this section. Take extreme care when working in the area of this label. The user must not disassemble the laser head for service or maintenance. Doing so will expose the user to uncontrolled laser radiation. Do not mount the laser at or near eye level for a person in the standing or sitting position; enclose beam paths whenever possible. Operate laser only under the direct supervision of a person knowledgeable in laser safety. Limit access to the laser area by spectators unless supervised. Provide protective eyewear suitable for 1064 nm output. Control all beam reflections. Post the area with laser safety warning signs. Ensure that no beams are emitted through windows, doors, etc. 8
WARNING: CAUTION: Use of controls or adjustments or performance of procedures other than those specified in this manual may result in hazardous radiation exposure. Opening or disassembling the head will result in damage even if it is not operating, and will void the warranty. The laser head is sealed and purged in a contamination-free environment. 1.3.3 Laser Emission Levels The 126-MOPA operates with a continuous wave (CW) 1064-nm emission of less than 18 W. There are two output windows, one for the main high-power output beam labeled MAIN and the other for a low-power beam sample labeled SAMPLE (see Fig. 1-3). The high-power emission is typically between 10 and 15 W and the low-power emission is typically between 40 and 60 mw. The low power beam sample can be used conveniently for beam monitoring or other measurement purposes without affecting the main highpower output beam. Laser diode emission is contained within the laser head. The power of escaping diode light is less than 25 µw. The diode emission wavelength is between 800 nm and 815 nm. 9
1.3.4 Safety Features and Labels Reproductions of the labels on the 126-MOPA system are given below in Figure 1-2. Warning Label: Class designation and warning label, located on top of the laser head. Aperture Labels (2): Located on the front of the laser head, below the 2 emission apertures, pointing towards the output beams. Certification Label: Located on the side of the laser head. Includes Model Number, Serial Number, Manufactured Date, Manufacturers Name and Address. This label is also used on the rear of the power supply. 1.3.5 Laser Head Safety Features Figure 1-2. Reproductions of laser safety labels. The Lightwave Electronics Series 221 incorporates several safety features to minimize the chances of harm or damage as a result of exposure to laser emission. The safety features of the laser head are described below, and their locations are given in Figure 1-3. 10
Figure 1-3. Laser head safety and certification label locations. 11
1.3.6 Power Supply Safety Features The safety features of the laser power supply are described below, and their locations are given in Figure 1-4. Figure 1-4. Power supply safety and certification label locations. Key Switch The laser cannot emit any radiation unless the key switch is turned to the ON position. The key cannot be removed in the ON position. Simply turning the key switch to the ON position does not necessarily imply the laser is emitting radiation, as the laser may be in the Standby Mode or the shutter may be closed. 12
Emission Indicator A light-emitting-diode (LED) indicator is lit when the laser key switch is turned to the ON position. The light is located on the front of the power supply above the key switch (Fig. 1-4). The indicator light is yellow or amber. It does not necessarily indicate the laser is emitting radiation, as described above. WARNING: Do not depend on the LED indicator for your safety! Failure of the emission indicator LED itself does not turn off the laser. If the LED should fail the laser will still operate. Some laser safety glasses will block or attenuate the light from the LED, or room light can overwhelm the LED light and make their emission invisible. The LED is provided strictly as a convenience. If the LED light does not come on when the laser is keyed on the laser should be serviced. Master Oscillator and Amplifier STANDBY Switches These switches are located next to the key switch and act as electrical attenuators for the 126-MO and the PA. When they are switched to the STANDBY position they turn off the laser diode within the 126-MO and the laser diodes within the PA, respectively. This is known as being in Standby Mode. More on the Standby Mode can be found in Section 3.2. When the diodes are off the laser can not produce dangerous light of any sort. Shutter Switch The shutter switch is located next to the Amplifier Standby switch and operates the shutter remotely. The shutter is located at the entrance of the PA and is intended to block the MO output beam before it can enter the PA. Note, that as a result of surface reflections from the MO-to-PA beam coupling optics, even with the shutter operated some low-power 1064-nm light (less than 2 mw) might still be emitted through the output windows. In order to be safe, the user must switch the MO into the Standby position as described in Section 3.2 of this manual and/or place a mechanical beam block in front of the output windows after the shutter has been operated. Make sure not to expose your hands or other body parts to the beam! Also, be aware that in case of a shutter failure if the MO is still on the beam block has to be capable of absorbing more than 10 W of 1064-nm light! Removing the beam block, turning the MO back into the Lase position and opening the shutter allows the laser radiation to exit from the laser head. WARNING: Although the shutter is intended as a safety feature, never rely solely on operation of the shutter for safety. Always wear eye protection when using the laser, even with the shutter closed. Safety Interlock 13
The user may disable the laser for safety purposes using the safety interlock provided. This interlock must be enabled in order for the laser to operate. The interlock is on the back panel of the power supply (see Fig. 4-1). This safety interlock comes with an "enable" jumper plug installed. An example of use of this interlock would be configuring the laser so that the interlock opens or closes when a door is opened or closed respectively. To use the interlock feature, remove the plug and connect switch (or relay) contacts across the input. Internally the sense circuit has a 10 kω pull-up resistor to +5 volts. If the interlock circuit is open, or the input voltage exceeds +2.5 volts, the laser will be disabled, and the power supply's display will read "ILCKOPEN". Once this interlock circuit is closed, the laser will implement a warm-up, as described in Section 3.1, and then return to the state it was in before opening the interlock. The interlocks are also described in Section 4.2 of this manual. 14