Viasho "FX series" Professional DPSS lasers white paper

Abstract

Solid state DPSS lasers have become increasingly popular due to their energy efficiency, high reliability, ruggedness, internal blanking and low Total Cost of Ownership (TCO). Solid state lasers are inherently smaller, more efficient and more reliable than traditional ion lasers as they contain no fragile gas tubes. The TCO of DPSS lasers is also lower due to their high efficiency and longer lifespan than conventional ion (gas) lasers. This paper provides background information on DPSS lasers as well as highlighting the features of the Viasho FX series compact DPSS lasers designed for laser show applications.

Introduction

Laser Entertainment systems have relied on bulky and fragile ion (gas} lasers for decades simply because that was the best choice available.  Originally conceived as laboratory instruments, ion lasers are ill suited to the rigors of entertainment applications where they are subjected to vibration, shipping by less than careful carriers, dust and dirt, unstable AC power and less than optimal cooling water supplies.
Laserists have traditionally worked around these obstacles by bringing power stabilization transformers and water works with pressure regulators and pumps to compensate for these problems.  The result was that an entire truck full of heavy equipment had to be be brought to even the simplest shows.  Many hours we spent dragging hoses and 3 phase power cables since the practical limits of air-cooled ion lasers was about 1 watt [although up to 8 watt air-cooled Copper Vapor lasers are available].
For medium and small size shows, laserists have longed for a simple to use, plug in the wall solution that would allow for a smaller system run from standard extensions cords and wall outlets without the need for cooling water.  In the late 1990's the solution appeared in the form of Diode Pumped Solid State (DPSS) lasers.  Rather then exciting a tube full of gas with a high voltage and then flushing away waste heat with running water, these units used rugged and reliable solid state infrared lasers and are generally air-cooled.  Infrared (IR) laser diodes are a well understood and mature technology which high reliability as their primary use is in the telecommunications industry.  IR diodes can be used to pump non-linear crystals capable of generating visible light.

Inside a DPSS Laser

Below is a simplified diagram of a DPSS laser.  There is a great deal more detail and complexity involved in the design and manufacture of these lasers but this diagram will suffice to explain the general principals.

A - A diode driver circuit is required to provide the current to the pump diode.  This circuit has to be very precise as IR diodes are very sensitive and easily blown.  For simplicity, the rest of the electronics involved in the laser are not shown.
B - Powering a DPSS laser is an infra-red laser diode, the pump diode, emitting at 808 nm.  This frequency is in the near infrared so is faintly visible to the eye as a very dim, deep red light.
C - In order to keep the output of the pump diode at exactly 808 nm, it is mounted on a Thermoelectric Cooler (TEC) as the output frequency of diode lasers is temperature dependent.
The TEC is an electronic device that transports heat from one side to another when electric current is passed through it.  It can be use to either cool or heat a device.  In a DPSS laser, the pump diode is attached to the "cold" side while the "hot" side is attached to a heat sink to dissipate the heat that is carried away from the diode through the TEC.  It can be simply controlled by sensing the temperature of the pump diode and then using an electronic circuit to regulate the TEC so as to keep the pump diode at the correct temperature such that the diode frequency is exactly 808 nm.
D - The beam output by the pump diode is not the circular beam that we are used to seeing from an ion laser thus complex beam shaping optics must be used. The pump diode has a "fast" axis in which the beam diverges widely, and a "slow" axis in which the beam diverges far less.  The beam shaping optics are used to make the beam from the pump diode as round as possible.  It is usually not possible to make a perfectly round beam so most DPSS lasers have a slightly elliptical beam where the beam can be as much as 2X bigger in one axis in some of the cheaper lasers.  In the Viasho FX series lasers, the beam is under 10% bigger in one axis making it almost round.
E - A second harmonic of the 808 nm pump diode light is generated by an ND:YVO4 crystal.  This converts the light from 808 nm to 1064 nm with is also IR light but is not visible to the eye.
F - For optimal performance, the ND:YVO4 crystal must be "temperature tuned" so it is also mounted on a TEC cooler with controller.
G - The 1064 nm light is sent to a KTP crystal which frequency doubles it to 532 green light.
H - The KTP crystal must also be "temperature tuned" so it is also mounted on a TEC cooler.
I - Just as in a traditional ion laser, an output coupler is used to form the laser resonator.
J - The 532 nm beam emitted from the KTP is very tiny and divergent.  Beam shaping optics are used to expand and coliminate the beam.
K - The final optic is an IR blocking filer.  This passes the 532 nm green laser beam and blocks any of the IR light from inside the laser that would otherwise be emitted.

Advantages of DPSS lasers

DPSS lasers have a number of important advantages that make them very desirable in laser show applications:

• They are solid state with no fragile gas filled tube which requires the gas pressure to be maintained correctly for optimal performance.

• DPSS lasers are more rugged that typical Ion lasers.  The do not require the complex resonator structure found in an Ion laser.  Because the optics are small, it is easy to adjust them at the factory and they generally stay in alignment for the lifetime of the laser - no more tweaking the optics before the show.

• DPSS lasers are very compact.  Typically they are very small and much lighter weight that ion lasers of similar power outputs (see picture below).

• DPSS lasers are very efficient.  Since they use IR laser diodes, they do not need high voltages to operate.  Ion lasers output about 2-3% of the AC power input as light, the rest is wasted as hear which is why higher power ion lasers require water cooling.  The DPSS lasers are fare more efficient converting about 25-30% of the electrical input into light.

• DPSS lasers are also less costly to manufacture than Ion lasers as they have fewer parts and there is no need for high voltage electronics and complicated plumbing.

• Solid state lasers have longer life spans that Ion lasers as they do not suffer from gas clean-up.  They have an almost unlimited shelf-life since they do not have to be run at regular intervals like Ion lasers as there is no need to maintain gas pressure.

• The IR diode in a DPSS laser can be modulated directly by the driver circuit.  Rather than using an external device (with inherent optical losses and alignment problems), the graphics system can turn the laser on and off directly as needed for blanking.  With analogue blanking, the laser power can be varied to produce different brightness in the image.

• Finally, and a major advantage for laserists, the 532 nm frequency produced by green DPSS lasers is very close to the peak of the spectral sensitivity in the human eye - the eye is very sensitive to lime green. Typically a 532 nm laser will appear between 3 and 4 times brighter than the same power of argon laser [when losses in the PCAOM are factored in].

TCO (Total Cost of Ownership)

One very important item is TOC or Total Cost of Ownership.  As an example, we can briefly compare the cost of a 100 mW argon laser with the cost of a 100 mW DPSS laser.
While the acquisition cost of a 100 mW Ion laser may be lower than a DPSS laser (especially if purchased used), the lifetime of the tube will typically be between 2,000 and 3,000 hours depending on him much shock, vibration and cooling problems it is subjected to in a touring application.   A DPSS laser will have a lifetime of 5,000+ hours.
Usually you will need at last one replacement tube for the argon laser laser in a 5,000 hour time period. Replacement tubes typically cost between 1/2 and 2/3 the price of the laser (including labour), not to mention the weeks of down-time and shipping to the manufacturer where your expensive repairs are endangered by commercial carriers.
Argon lasers have complex, high voltage, heavy power supplies that blow up on a regular basis so cost of maintenance is higher for Ion lasers.
Another item to take into consideration is the blanking device.  With an Ion laser, you will have to use a galvo or PCAOM for blanking which should be added to the cost of the laser.  This expense is unnecessary with the Viasho FX series as they have internal blanking,. As an added benefit, you do not loose any light in an external blanking device.
The DPSS lasers have the advantage of operating on much lower amounts of power and lower voltages so it is possible to make the electronics very reliable.  Since the Viasho FX series DPSS lasers will operate for 5,000+ hours with little or no maintenance, the cost of ownership is much lower even though the initial cost of purchase may be higher than a comparable argon laser.

Viasho FX series DPSS lasers

The Viasho FX series lasers offer improvements and enhancements on typical DPSS lasers which were implemented to meet the needs of laser professionals:

• The one piece design gives you a very compact and light weight laser - up to 200+ mW in the palm of your hand.  the Viasho FX series is so compact and lightweight, than you can consider carrying one as a "spare laser" with your regular rig just in case of problems with your Ion laser.  While it may not offer as much power, it can save your bacon at a show as the graphic/animation portion of the show can still be presented.

• The FX series one piece design also eliminates one of the major failure modes in DPSS lasers - static discharge thought the umbilical connecting the head and the PSU.  Pump diodes are very sensitive and in many cases, special static elimination procedures must be used when connecting and disconnecting the laser head and PSU.  Some owners keep their PSU and head permanently connected to avoid this problem making the laser difficult to handle.  The Viasho FX series eliminates these problems entirely by providing a small and simple to use one-piece laser.

• Viasho FX series lasers are also very simple to use.  Just plug AC power into the back with a two pin line cord of the type typically used with laptop computers, connect the blanking signal and you are ready to lase.  The universal AC power supply accepts a wide range of voltages form 100 to 250 VAC at 50 or 60 Hz.  You can operate the Viasho FX series lasers from any wall outlet in the world... and if you don't have the right plug on the end of your cable, just go to the local computer store!

• The Viasho FX series lasers have internal blanking so no external blanking device is required.  You just plug the blanking signal into the mini BNC connector on the back of the laser (see photo below).  This cuts set-up time as there is no need to align the blanking and there is no optical loss in a blanking device.  While some DPSS lasers offer internal blanking, often this is at very slow (sub 5 K) speeds.  While this is fine for beam effects, high speed graphics systems need to be able to blank faster when projecting complex images.  While the FX series laser can be modulated at speeds of up to 50K, there is "optical capacitance" inherent in any DPSS laser so there is a finite decay time in the system when it is turned on and off at very high speeds.  For practical purposes, the blanking speed of the FX series is around 25K which is more than sufficient for high quality graphics.

• The beam quality on the Viasho FX series has been optimized to give lower divergence than most typical small DPSS lasers.  The new analogue blanking models that will be introduced shortly will have even lower divergence than the present models.

• Viasho recognizes that reliable power output is important to laserists.  Precision electronics keep the laser temperature stabilized to maintain output power.  All Viasho FX series lasers are delivered after an extensive burn-in and testing at the factory with output at least 5% over specifications to account for the inevitable slight drop in power that occurs in any DPSS laser after it has been in operation for some time.

• Finally, as with all DPSS lasers, the 532 nm green has a higher perceived brightness that an argon laser of the same power.  The FX series allow you to perform you shows anywhere in the world with a high brightness laser than can fit in your coat pocket and which is more rugged, reliable and has lower cost of ownership than an Ion laser that appears the same in brightness.

Summary

The Viasho FX series offers laserists a compact, efficient, rugged and reliable laser system in a convenient one-piece unit with good beam quality and a choice of output powers from 50 to 200 mW. The FX series lasers are delivered after extensive testing at the factory with at least 5% over specification power.  The high perceived brightness of the 532 nm lasers make the FX series an ideal replacement for small argon lasers.  Internal high speed blanking means no loss of light, or extra costs due to an external blanking device.
Viasho has teamed up with Laser F/X International to bring you these exceptional lasers at factory direct prices.  Laser F/X will provide full applications and technical support for the FX series so you can be assured you will get the correct information you need from a laserists perspective.

ORDERING

To order your Viasho FX series DPSS laser, see the purchasing information on the main page or send E-mail to viasho@laserfx.com

viasho@laserfx.com

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