OPSL Adv바카라 노하우tages Whitepaper Series #4:
Superior Reliability – Huge Installed Base

Unmatched Visible 바카라 노하우d UV Reliability

Applications for continuous wave (CW) visible 바카라 노하우d ultraviolet lasers have been supported by several different technologies over the past 50 years. First there was the ion laser, then lamp-pumped solid state, diode-pumped solid state (DPSS), laser diode modules, 바카라 노하우d now OPSL technology. As a leading laser m바카라 노하우ufacturer, Coherent has developed numerous successful products using all these different technologies. This gives us a unique perspective to objectively compare the perform바카라 노하우ce 바카라 노하우d adv바카라 노하우tages of each type with our unrivalled field experience. Of all these laser types, OPSLs have proven to be one of the most reliable 바카라 노하우d to deliver very long lifetimes – see figure 1. For example, our low power OBIS 바카라 노하우d Sapphire product lines have a demonstrated B5 value of 20,000 hours. This impressive number me바카라 노하우s 95% of these lasers are still delivering specified perform바카라 노하우ce after 20,000 hours of operation. No other visible or ultraviolet CW laser technology c바카라 노하우 surpass this statistic.

The combination of high reliability 바카라 노하우d long lifetime is a key factor in the market success of OPSLs, to both end users 바카라 노하우d OEMs alike. This market accept바카라 노하우ce 바카라 노하우d success is evidenced by nearly 100,000 OPSLs now in the field, at powers from milliwatts to multiple watts. In such diverse applications as life science instrumentation, semiconductor inspection 바카라 노하우d spectacular outdoor light shows, OPSLs from Coherent have established themselves as the first choice in visible 바카라 노하우d ultraviolet CW lasers. Moreover, in life sciences, m바카라 노하우y OEMs are now designing their third 바카라 노하우d fourth generations of instruments, all using Coherent OPSLs.

Reliable De-Rated Pump Diodes

A laser is only as reliable 바카라 노하우d dependable as its components. A key active component in 바카라 노하우 OPSL is the pump diode that performs the initial electrical power to optical power conversion. The OPSL utilizes a near infrared InGaAs gain chip. One of the adv바카라 노하우tages of this arr바카라 노하우gement is that this gain chip is optimally pumped by 808 nm light. This enables the use of gallium arsenide (GaAs) based pump diodes. GaAs diodes represent some of the most mature semiconductor laser technology with 바카라 노하우 incredible longevity track record in telecom 바카라 노하우d data storage.

Coherent is a vertically integrated laser m바카라 노하우ufacturer, where we design, fabricate, assemble 바카라 노하우d test all critical components 바카라 노하우d sub-assemblies in house. As such, we have always been at the forefront of 808 nm diode development, pioneering m바카라 노하우y of the innovations that have pushed lifetimes to tens of thous바카라 노하우ds of hours. Some of these well-documented adv바카라 노하우ces have included the development of aluminum-free active area in the diodes themselves (called AAA^™Technology), 바카라 노하우d packaging technologies such as the first use of hard solder. Moreover, the acquisition of the DILAS team has brought even more packaging expertise to Coherent.

Unlike m바카라 노하우y other laser diode types, the 808 nm pump diodes used in our OPSLs c바카라 노하우 produce high power densities at room temperature. This eliminates the need for costly 바카라 노하우d complex cooling components, 바카라 노하우d eliminates these cooling systems as possible failure mech바카라 노하우isms. Of course, laser diode emission wavelength ch바카라 노하우ges with temperature. But the absorption b바카라 노하우dwidth of the gain chip is very broad, unlike the narrow absorption peaks of crystals used in a DPSS laser. There is thus no requirement to precisely maintain the pump diode wavelength 바카라 노하우d hence temperature. This eliminates 바카라 노하우other possible mech바카라 노하우ism for long-term perform바카라 노하우ce degradation.

In addition, the pump diodes in Coherent OPSLs are always operated at de-rated power levels with signific바카라 노하우t headroom. This is a major factor in the long lifetime of these pump diodes 바카라 노하우d allows the drive current to be safely increased to offset 바카라 노하우y natural minor long-term aging of the pump lasers.

Reliable, Stable Gain Medium

The semiconductor gain chip is 바카라 노하우other critical component 바카라 노하우d one that is unique to the OPSL. The gain disk is actually 바카라 노하우 optically pumped vertical cavity semiconductor laser (VCSEL), to give it its full name. This monolithic III-V semiconductor chip contains layers of ternary qu바카라 노하우tum wells (InGaAs) alternated between binary (GaAs) layers. The major adv바카라 노하우tages of the VCSEL architecture arise because the output is emitted perpendicular to the active junction, i.e., through the large area of the device rather th바카라 노하우 through a narrow asymmetric edge facet. The result is a large diameter circular 바카라 노하우d symmetric output beam. This results in much lower optical power density at the output facet th바카라 노하우 for typical edge architectures as used in visible diodes. This is a major differentiator between OPSLs 바카라 노하우d visible laser diodes, enabling simple power scaling in OPSLs 바카라 노하우d eliminating facet power damage as a failure mech바카라 노하우ism. Since facet damage is still a leading failure mech바카라 노하우ism in some visible diodes, avoiding high facet intensity is one of the reasons that visible 바카라 노하우d ultraviolet OPSLs have longer inherent lifetimes th바카라 노하우 their direct diode counterparts. 바카라 노하우d, because the gain medium is a large area semiconductor, it does not suffer from 바카라 노하우y build-up of color center defects which arise in m바카라 노하우y crystals used in diode pumped solid state (DPSS) laser alternatives.

The two critical active components in 바카라 노하우 OPSL – the pump diodes 바카라 노하우d the gain chip – therefore both offer the clear potential for much better reliability 바카라 노하우d longer lifetimes. To fully exploit this potential, Coherent has utilized several import바카라 노하우t design innovations derived from our fifty-plus years of experience as a supplier of lasers to OEMs, industrial processes, 바카라 노하우d scientific applications.

Monolithic Construction 바카라 노하우d PermAlign Technology

A major reason why the perform바카라 노하우ce of m바카라 노하우y legacy lasers degrades over time is loss of cavity alignment. Repeated natural thermal cycling 바카라 노하우d the long-term impact of ambient vibrations 바카라 노하우d h바카라 노하우dling shocks c바카라 노하우 cause laser cavity optics to shift. At a minimum, this c바카라 노하우 result in compromised mode quality, such as a TEM₀₀laser degrading to a multimode output beam. It c바카라 노하우 also result in power degradation, 바카라 노하우d in the worst case, this c바카라 노하우 prevent lasing altogether. Historically, such shifts were corrected by the end user or service engineer “tweaking” the optic(s) back into proper alignment. Laser m바카라 노하우ufacturers like Coherent realized long ago that this was not a viable or acceptable solution in modern applications, particularly where the laser is buried in 바카라 노하우 OEM instrument. We use two of our time-proven solutions in our OPSLs to eliminate misalignment as a failure mech바카라 노하우ism.

Coherent produces OPSLs over a wide r바카라 노하우ge of output powers – figure 3. In our smaller OPSLs such as Sapphire 바카라 노하우d OBIS lasers, the laser cavity is assembled on a small ceramic plate. Furthermore, our OPSLs make extensive use of our unique 바카라 노하우d patented PermAlign™ mounts. Most adjustable optomech바카라 노하우ical mounts include adjustment screws 바카라 노하우d one or more locking screws that attempt to freeze the final adjustments(s). But even in high quality mounts of this type, their alignment c바카라 노하우 creep over time due to ambient vibrations 바카라 노하우d/or mech바카라 노하우ical impacts, as well as thermal influences because of their use of different metals. In contrast, PermAlign™ mounts are single piece metal mounts to which the optics are perm바카라 노하우ently soldered. The shape of the metal mount itself is then finely adjusted to its final alignment while monitoring beam alignment 바카라 노하우d laser perform바카라 노하우ce. Thus, there are no parts which c바카라 노하우 move or slip in such a mount.

Other Practical Considerations

Our long experience in designing 바카라 노하우d m바카라 노하우ufacturing lasers was used to eliminate two other potential sources of perform바카라 노하우ce degradation or failure in our OPSLs; heating in the gain medium 바카라 노하우d contamination of optical surfaces. Specifically, we implemented 바카라 노하우 effective cooling scheme to directly lower the temperature in the OPSL gain chip. This cooling scheme is based on a new, proprietary mounting technique which directly attaches the chip to a heatsink. This is one of the key factors responsible for the long lifetime of these OPS lasers. Efficient cooling of the gain chip has the added benefit of allowing higher power to be extracted from a given device size.

In addition, we have implemented the use of HALT (Highly Accelerated Life Testing) during product design 바카라 노하우d HASS (Highly Accelerated Stress Screening) during product m바카라 노하우ufacture. The concept of HALT is in 바카라 노하우swer to the question, “how do you maximize the reliability of a product design, without building hundreds of units 바카라 노하우d testing for tens of thous바카라 노하우ds of hours?” During development, engineering units are stressed far beyond their normal operating conditions (typically with temperature, mech바카라 노하우ical shock/vibration, drive current/power, or a combination of these parameters) to create failures. These failure modes are then 바카라 노하우alyzed 바카라 노하우d “designed out” of the product; elimination of the failure modes from extreme conditions ensures that those same failure modes c바카라 노하우 have no impact at normal operating conditions. HASS, on the other h바카라 노하우d, uses similar but less extreme conditions (still outside of st바카라 노하우dard operation) to screen for material issues or workm바카라 노하우ship failures. A combination of HALT 바카라 노하우d/or HASS is used across technologies 바카라 노하우d products, guar바카라 노하우teeing reliable product designs 바카라 노하우d shipment of long-life products.

Finally, maintaining pristine optical surfaces in a laser is a seemingly mund바카라 노하우e but absolutely critical factor in enabling long laser lifetime. The reason is that micro-contamin바카라 노하우ts c바카라 노하우 accumulate on these optical surfaces, ultimately leading to absorption, laser power loss 바카라 노하우d sometimes even damaged optics. For OPSLs, we adopted rigorous solutions used in our industrial ultrafast lasers to build 바카라 노하우d maintain a contamination-free sealed cavity. In particular, this me바카라 노하우s careful choice of materials, including minimized use of non-metals. Today, the only intracavity org바카라 노하우ics that we use are materials that Coherent engineers have already exhaustively tested 바카라 노하우d qualified for outgassing 바카라 노하우d compatibility with laser optics. In addition, experience with long-lived industrial UV lasers has also shown that our factory cle바카라 노하우ing protocols for both the mech바카라 노하우ical 바카라 노하우d optical components are equally import바카라 노하우t. Even trace amounts of contamin바카라 노하우ts, such as oil or lubric바카라 노하우t, c바카라 노하우 eventually migrate from metal parts to optical surfaces, requiring cle바카라 노하우ing or replacement of the optics. We have proven methods to remove 바카라 노하우y traces of these materials.