Menlo Systems C-Fiber 780 Fiber Lasers

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System Description | Hazards | Approved Users | Documentation | Controls | Recommended Practices | Maintenance | Emergency Procedures | Revision History

System Description

The C-Fiber laser series consists of erbium-doped femtosecond fiber lasers with a 100 MHz repetition rate. In the IREAP lab (ERF 0205A), there are two identical (laser A and B) C-Fiber femtosecond lasers operating at 1560nm. The lasers can also generate 780nm output which is generated via a SHG process on 1560nm beam.

In addition to the main laser system, there is an electrical synchronization system. This system was designed to do asynchronous optical sampling (ASOPS) which allows high-speed scanning over 10ns(=1/100MHz) of time delay without a mechanical delay line.

  • Manufacturer:  Menlo Systems
  • Product Name(s):  C-Fiber 780
  • Serial Number:  1370G
  • UMD Property Tag:  202846
  • Manufactured Date:  6/2010
  • Location:  ERF 0205a
  • Laser Type:  Ultrafast mode-locked fiber laser, with frequency doubling
  • Laser Classification:  Class IV
  • Wavelength (Center):  1560nm±20nm, 780nm±20nm
  • Repetition Rate:  100 MHz
  • Pulse Duration:  <90 fs
  • Timing Jitter:  2 fs RMS
  • Average Power (energy): 100 mW (1560 nm), or 65 mW (780 nm)
  • Beam Diameter:  Approx. Gaussian, with 1/e2 width of 1.8 mm
  • Polarization:  linear, s-polarized

Hazards

Femtosecond lasers are Class IV lasers. Wear appropriate goggles when adjusting and operating. There may be back reflections from optical surfaces within the optical setup. Take measures to block any unwanted beams.

Approved Users

All users must have completed the mandatory Laser Safety training: https://des.umd.edu/risk_comm/edu/training.cfm Further, all users must receive proper safety training from the PI, other authorized users, or Coherent service technician before operating the Libra.  The following are currently authorized users:

  • Mehdi Jadidi
  • Kyowon Kim
  • Shanshan Li
  • Ryan Suess
  • Jeremiah J. Wathen

When the laser is in use, a sign should be placed on the door, advising all visitors and laboratory personnel of the wavelengths in use.  All personnel entering the laboratory (whether or not they are using the laser) must wear the appropriate laser safety eyewear.

Required training:

  • Online laser safety training — http://www.des.umd.edu/risk_comm/edu/training.cfm
  • UMD Laser Safety training course (schedule via the UMD LSO, Steve Hand, hand@umd.edu)

Visitors may be permitted in the lab while the MenloSystems Fiber Laser is operating, but only under the following conditions:

  1. The visitor has donned the proper eye protection (> OD 5 @ 1560nm and(or) 780nm).
  2. The visitor has been briefed on the paths of all beams in the lab.
  3. The beam-path is enclosed to the extent possible, with all beams terminated properly (i.e., in folded metal beam dumps or razor-stack beam dumps).
  4. No adjustments are made to the beam-path while the visitor is present.
  5. The laser’s cavity must be enclosed while the visitor is present.

Documentation

There are hardcopy manuals for MenloSystems laser, its electronic synchronization system, and the ASOPS technique in the Kim lab(KEB 2135). The FiberLaser Software v0.9.5 and the software manual are on the PRL shared folder.  A brief documents describing the system specifications can be found on Thorlabs website.

Controls

  • During alignment of the beam, wear suitable eye protection protection (> OD5 @ 1560 nm and(or) 780nm).
  • Inform all personnel having access to the lab prior to aligning/re-routing the beam.
  • Keep the beam path free of combustible material.
  • Avoid exposure of the skin and eyes to direct or scattered laser light.
  • Turn off the laser or close the output shutter when the laser is not in use.
  • To reduce the possibility of eye damage, maintain a high ambient light level in the laser operation area during normal operation.
  • Unless actively aligning the laser, maintain the cavity cover installed at all times.
  • Avoid wearing reflective objects such as jewelry or watches while in the laser operation area.
  • If you want to leave the lab for a short time, shutter the laser.

The recommended eyewear (>OD5 @ 1560 nm and(or) >OD5 @ 780 nm) can be found in the goggle locker in the IREAP lab(ERF 0205A).

Recommended Practices

In the original factory design, the 1560nm pulse goes to a second harmonic generation (SHG) setup to generate the 780nm, and the two outputs(1,2) are the generated second harmonic (780nm) and the leftover signal (1560nm) from the SHG process.

In order to get the highest possible output power at 1560nm, the lasers have been slightly modified from the original design. A mirror(4) on a flip mount was installed on the optical path to send the 1560nm pulse out of the cover, before it goes to the SHG process. Accordingly, a third output hole(3) on the cover was drilled in our lab for this deviated 1560nm beam.  In most cases, the system is usually configured to operate at 1560nm, thereby bypassing the frequency doubling crystal, such that the light emerges from the third output (3).   In this configuration, the first two outputs are dark.

 

 

Standard day-to-day operating procedures for the Tsunami can be found in Chapter 7 of the Tsunami’s manual. Key points and additional guidance follow here.

System Startup and Normal Operation

  1. Verify the Model 3955 electronics module is on. The Model 3955 electronics module should remain on at all times to maintain thermal stability of the Tsunami’s acousto-optic modulator.
  2. Ensure the chilled water system is operating prior to admitting the pump beam to the Tsunami’s cavity. Verify the chiller is operating with a temperature setpoint of 18°C.
  3. Block the output of the Tsunami with a power meter or suitable beam block. Switch on the pump laser (the Verdi) and open the pump shutter. Typically, the Verdi should output > 9.6 Watts in order to obtain >1.8 Watts output from the Tsunami. Allow a minimum of 10 minutes after switching on the pump laser before optimizing the Tsunami’s output power. The pump laser (the Verdi) takes time to reach thermal equilibrium.
  4. Optimize power output from the Tsunami and start mode-locking

Mode Locking procedure:

  1. Project the Tsunami’s output onto a suitablel power meter.
  2. While monitoring the output power on the power meter and the PHOTODIODE LED indication on the 3955 electronics module, adjust mirrors M10 and M1 for maximum output power and note the power level. You should easily be able to obtain > 1.8 Watts out of the Tsunami (@ 810 nm). You can often increase output power a little more by “walking the beam.” See the “Optimizing Laser Output” procedure in Chapter 7 of the Tsunami’s manual. At least 1.85 Watts of power from the Tsunami is required to drive the Opal. Only an experienced operator of the Tsunami should attempt to adjust cavity mirrors other than M1 and M10. Severe misalignment can occur. If you are new to the Tsunami and cannot obtain sufficient output power by simple adjustments of M1 and M10, obtain help from an experienced user.
  3. After optimizing output power, project the Tsunami’s output onto an optical spectrum analyzer. Depress the STATUS mode locker enable button (the ENABLE LED should illuminate). Observe the spectrum to verify proper mode-locking. Verify the laser’s bandwidth and ensure there is no “CW breakthrough.” See Figure 6-14 in the Tsunami’s manual as a reference. If the Tsunami does not spontaneously mode-lock, it sometimes helps to “jog” the dispersive optics and/or gently tap on the cavity enclosure: Deactivate the STATUS mode locker enable button. While monitoring the laser spectrum, quickly jog the dispersive prisms by rapidly rotating the prism operator. Be sure to return the prisms to their original position. If mode-locking starts, re-activate the STATUS mode locker enable button. If mode-locking cannot be achieved, re-optimize the Tsunami’s output power and try again.
  4. After operating for approximately ½ hour, the Tsunami should reach equilibrium. Small adjustments during this time may be necessary to maintain optimum power output and mode-locking.

Maintenance

The Tsunami is cooled by a closed-loop chilled water system. The coolant flows through a solid block heat exchanger, which cools the laser’s Ti:sapphire rod. It is recommended that the chilled water be replaced every three months, to prevent deposition of algae and other organic matter on the internal walls of the heat exchanger and throughout the chilled water system.

Caution: Do not replenish the chilled water with de-ionized water. De-ionized water is corrosive. Use only distilled water in the chilled water system.

Caution: The timing of the circuitry in the Model 3955 electronics module was tuned during installation. Do not replace the BNC cables that connect the Model 3955 to the Tsunami. Doing so will affect the phase delay of the active mode-locking circuit.

Emergency Procedures

In the case of a medical emergency (e.g., you or a colleague suffer personal injury due to accidental laser exposure) contact UM Emergency (Fire-Police-Rescue) immediately. In the case of non-injury related emergencies, follow standard shut down procedures for the Opal-Tsunami laser system and contact an authorized user. The following table gives relevant emergency contact numbers.

UM Emergency (Fire-Police-Rescue) #911
Environmental Safety (Main Office) 301-405-3960
Laser Safety Officer (Steve Hand) 301-405-3985
University Health Center Occupational Health Medical Consultation and Evaluation 301-314-8172
T. E. Murphy, PI 301-405-0030, tem@umd.edu

Revision History

    • Created:  10/15/2013 (Jeremiah J. Wathen)