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Optics FAQ


 

How can I increase the depth of field of my lens?

Increase the f-number (decrease the aperture size). This may require increased lighting. However, very large f-numbers (>f/22 image side working f-number) will significantly degrade the lens resolution.

Why are custom lenses so much more expensive than lenses from stock?

The cost of manufacturing optics is extremely volume dependent. Mass-produced lenses provide excellent performance at low cost. Lenses produced in small quantity can cost five to twenty times more. It is always worth attempting to use or adapt a mass-produced lens for an application before designing a custom lens.

Helpful Definitions

  • Continuous Wave
    Laser power is fixed or variable, but not delivered in a discrete pulse envelope.
  • Pulsed
    Laser energy is delivered in a single discrete pulse at a specified repetition rate.
  • Power
    The average power of a continuous wave (cw) laser beam expressed in watts (W).
  • Energy per Pulse
    The energy of an individual pulse expressed in joules (J).
  • Pulse Repetition Rate
    The rate at which pulses are repeated in a uniformly pulsed train of pulses expressed at the frequency of repetition of the pulses in the unit of hertz (pulses per second, Hz).
  • Gaussian Criteria
    The definition as used in the ANSI Z136.1 Standard for both beam diameter and beam divergence, require that these quantities be measured at the 1/e power point (63.2%) on the ideal Gaussian beam intensity profile. Note that most laser equipment manufacturers specify these beam properties at the 1/e2 power point (86.5%), which is a factor of 1.414 larger than the 1/e power point.
  • Beam Dimension
    Beam size (typically diameter) in millimeters, measured on the longest dimension.
  • Beam Divergence
    Change in beam size with respect to distance measured in milliradians.

I have an older Melles Griot Laser, part number 05-LHP-151 that I need to replace, but I can't find the same part number in the new catalog. Is it still a current product?

Yes it is. In our previous catalogs, we sold the laser heads and the power supplies separately, whereas in our new catalog we have grouped them together to be sold as systems. We found that most people ordered both the laser head and its appropriate power supply on the same orders, so we decided to sell them as a system to make it easier on the consumer.

The 05-LHP-151 is the part number for just the laser head while the new system part number 25-LHP-151-249 designates the same laser head with its corresponding US power supply.

We understand that our customers may only need to buy just the laser head or just the power supply, so we still sell them individually.

Commonly, we can still supply a laser head or power supply, but just haven't listed it in the catalog or on the website. This particularly applies to our older components. Most of the time these are still available and can be purchased by calling us directly.

Simply contact the Melles Griot's Applications Engineering department to find the appropriate parts: Customer Support.

What is the Doppler broadened gain width of a Helium Neon laser?

Helium Neon lasers can range from 800 MHz to 1575 MHz full-width-at-half-maximum (FWHM) depending on the design. The typical 632.8nm HeNe is 1400 MHz. The width of a single mode located under the gain curve is typically 1 MHz.

Can a Helium Neon laser be re-gassed?

While re-gassing can provide some extension of the output performance in some gas lasers like the CO2, Argon and the higher powered side arm HeNes (which have external optics), it is not recommended or provided for smaller internal mirror coaxial tubes. Typical end-of-life failure for a HeNe is cathode sputtering. This occurs when the protective oxide layer on the cathode is expended through continuous bombardment by the laser discharge. There is no cost effective way of regenerating this layer. When the oxide layer is expended, the discharge itself vaporizes the "raw" aluminum and deposits this material, in its vapor state, on other surfaces such as the optics and the glass bore.

What agency approvals are available for the Melles Griot Helium Neon lasers?

Most of our HeNe laser heads are CDRH / CE certified. Certified product for CDRH falls under one of the following classifications: Class II (<1.0mW), ClassIIIa(<5.0mW) or Class IIIb(<575mw). For CE our lasers are certified as a class 2 or 3B. Plasma tubes including some laser heads are not certified. In this case, it is the responsibility of the end-user to certify their system by meeting agency approvals. If CDRH / CE certification is a requirement for your system, be sure to verify the laser you select meets your needs.

Which power supply can I use to operate my Helium Neon laser?

All Melles Griot HeNe lasers have a recommended Laboratory or Module power supply (AC and DC input versions available), typically listed on the laser's specifications sheet. If you are unsure which one is appropriate, please call us at 1-800-835-2626 and ask for a Laser Applications Engineer.

Rule of thumb in choosing a power supply: If you know the operating voltage and current of your laser, the power supply must have a voltage range large enough to fit the operating voltage for the laser and must be set at the appropriate operating current.

What is the Temporal Coherence length of a Helium Neon laser?

Coherence length is defined as the length over which energy in two separate waves remains constant. With respect to the laser, it is the greatest distance between two arms of an interferometric system for which sufficient interferometric effects can be obtained:

L = C / V

Where L is the Coherence Length, C is the speed of light and ν is the laser’s spectral line width

Coherence length will vary from laser to laser as a function of the Doppler broadened gain width; however, for a HeNe 20 - 30 cm is typical.

How can I prevent my vision optics from moving out of adjustment?

Optical mounts for on-line applications should be rigid, have positive locks, and have no more than the required adjustments. Laboratory mounting fixtures are generally not rugged enough for permanent on-line installations.

How should I mount my video camera and lens?

Machine vision optics should be mounted firmly but should not be stressed by excessive force. Do not rely on the camera C-mount thread to support heavy lenses. Either mount the lens and let the camera be supported by the lens, or provide support for both. Avoid over-tightening lens mounting clamps.

Do telecentric lenses have larger depths of field than other lenses?

No. The image from a telecentric lens remains in focus over the same depth of field as that of a conventional lens working at the same f-number. Telecentric lenses provide constant magnification at any object distance. Therefore, they make accurate dimensional measurements over a larger range of object distances than a conventional lens.

Do telecentric lenses have less distortion than other lenses?

In optics, "distortion" is the name of a specific aberration inherent in lens designs. Telecentric lenses offered by Melles Griot have low distortion. However, low distortion and telecentricity are separate, unrelated lens parameters.

Can I change the magnification of my telecentric lens?

No. By definition, a telecentric lens has a fixed magnification. Melles Griot offers a variety of telecentric lenses with large selection of magnifications.

Is there a telecentric lens with a very large field of view?

Because the first element of a telecentric lens must be larger than its field of view, telecentric lenses are generally restricted to fields of less than six inches. Larger fields of view are possible in some applications, including web inspection, using line-scan cameras.

I have a lens/filter/mirror/optic that I purchased from Melles Griot and I want to clean it. What cleaning methods are recommended for my item?

The recommended cleaning methods are dependent on the type of optic and its coatings.

You can download the recommended Melles Griot cleaning procedures document Cleaning Methods (PDF). The first part of the document describes five separate cleaning procedures with step-by-step instructions. The second part of the document lists which procedures should be used for which component.

You can also download this article Cleaning Optics (PDF) which explains the importance of the cleaning process to improve both the lifetime and performance of optics. Proper materials, techniques and handling procedures should be used to minimize the risk of damage.

I want to permanently attach fibers. Can the autoalignment piezoactuator controller follow relative movements during a bonding process?

Yes, the auto alignment piezoactuator controller has the ability to accommodate movements between a device and fiber during a pig tailing operation. However, when attaching fibers, two options are available, depending on the response of the throughput signal to the bonding process itself.

  1. Remain in TRACK mode — The auto alignment piezoactuator controller follows any relative movements by constantly and automatically optimizing throughput power.
  2. Switch to LATCH mode — this freezes the vertical and horizontal positions at optimum coupling.

I'm providing my own power to the OEM shutter drive board. What are specs for the necessary power cord and power supply?

The power connector/cord we use is a Mouser Electronics #172-4201 (mouser.com / tel. 800-346-6873). Ref. Shutter Pwr Cable - Mouser 172-4201.pdf

The recommended power supply is 12VDC, regulated, 3 Amp (providing some "reserve" over the 2.5A max load).

I'm using the OEM shutter board with TTL control. What are the proper DIP switch settings?

For direct TTL control of shutter "ON" time, DIP switches DS-1 & DS-2 should be ON. DS-3 should be OFF. On-board timer pot R3 should be set to it's minimum value (full CCW). Maintain the TTL pulse as long as required to get desired shutter timing.

For on-board control of shutter "ON" time, all DIP switches should be ON. Initiate the shutter drive with a short TTL pulse (i.e., 20mS). Set on-board timer pots as needed to get desired shutter timing.

Notes - The shutter will not actuate if DS-2 and DS-3 are both OFF. See Operating Instructions sheet #25164B for more complete information.

When the shutter is closed, is the transmission zero?

For standard (black-painted metal) shutter blades, the transmission is essentially zero.

What is the light power that can safely be incident on the closed shutter without affecting its performance?

Maximum allowable light level will depend on many factors (wavelength, duration, blade material, blade coating, and environmental conditions), generally limited by coating damage and/or warping of shutter blades. Although we do not rate shutters for specific light levels, we can provide sample blades for application-specific testing by customers.

Contact a Melles Griot Applications Engineer for sample blade arrangements.

How does the X synchronization work?

When the shutter blades are fully open (or fully closed for a normally open shutter); a dry contact is made with the X-synchronization, which provides electrical continuity.

May I use a lower DC signal than the recommended 4X the rate solenoid voltage to open or close the shutter?

We recommend only using the recommended 4X voltage pulse for 20mS; Using any lesser voltage will result in less reliable shutter actuation.

What are the operational specifications for the Standard and Ultrathin Electronic Shutters?

Shutters operated outside these conditions may function reliably.

Specifications:

Operational
Maximum Repetition: 2 Hz 
Minimum Recharge Time: 200 msec (from de-energized to next actuation) 
Duty Factor: < 100% (NOTE 1) 
Service life: >100,000 actuations

Environmental
Operating Temperature: -10C to + 40C
Humidity: Non-condensing
Shock/Vibration Resistance: To be verified by user, within system

What is the laser damage threshold for the shutters blades?

We do not have a documented laser damage threshold for our Spring-Steel Blades with a Teflon-impregnated black matte finish. If this is a concern for your application Melles Griot will send you a shutter blade for testing.

Are the Melles Griot laser beam divergence angles which are specified in the laser specifications the half angle values or the full angle values?

The full angle values

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