What does the VTEC system in a engine do?

If you have read How Car Engines Work, you know about the valves that let air into the engine and let exhaust out of the engine. You also know about the camshaft that controls the valves. The camshaft uses rotating lobes that push against the valves to open and close them. Check out How Camshafts Work for more information.
It turns out that there is significant relationship between the way the lobes are
ground on the camshaft and the way the engine performs in different rpm(rotations per minute) ranges. To understand why this is the case, imagine that we are running an engine extremely slowly -- at just 10 or 20 rpm, so it takes the piston seconds to complete a cycle. It would be impossible to actually run a normal engine this slowly, but imagine that we could. We would want to grind the camshaft so that, just as the piston starts moving downward in the intake stroke, the intake valve would open. The intake valve would close right as the piston bottoms out. Then the exhaust valve would open right as the piston bottoms out at the end of the combustion stroke and would close as the piston completes the exhaust stroke. That would work great for the engine as long as it ran at this very slow speed.
­W­hen you increase the rpm, however, this configuration for the camshaft does not work well. If the engine is running at 4,000 rpm, the valves are opening and closing 2,000 times every minute, or thirty to fourty times every second. When the intake valve opens right at the top of the intake stroke, it turns out that the piston has a lot of trouble getting the air moving into the cylinder in the short time available (a fraction of a second). Therefore, at higher rpm ranges you want the intake valve to open prior to the intake stroke -- actually back in the exhaust stroke -- so that by the time the piston starts moving downward in the intake stroke, the valve is open and air moves freely into the cylinder during the entire intake stroke. This is something of a simplification, but you get the idea. For maximum engine performance at low engine speeds, the valves need to open and close differently than they do at higher engine speeds. If you put in a good low-speed camshaft, it hurts the engine's performance at high speeds, and if you put in a good high-speed camshaft it hurts the engine's performance at low speeds (and in extreme cases can make it very hard to start the engine!).
VTEC (which stands for Variable Valve Timing and Lift Electronic Control) is an electronic and mechanical system in some Honda engines that allows the engine to effectively have multiple camshafts. As the engine moves into different rpm ranges, the engine's computer can activate alternate lobes on the camshaft and change the cam's timing. In this way, the engine gets the best features of low-speed and high-speed camshafts in the same engine. Several of the links below go into the actual mechanics of the VTEC system if you are interested.
Several engine manufacturers are experimenting with systems that would allow infinite variability in valve timing. For example, imagine that each valve had a solenoid on it that could open and close the valve under computer control rather than relying on a camshaft. With this type of system, you would get maximum engine performance at every rpm range. Something to look forward to in the future...
POSTED BY:ABDUL ZAHIR JAN MAGSI
http://www.howstuffworks.com/question229.htm

What Next-Gen Tech, Gadgets Are You Most Looking Forward To?

Motorola Atrix 4G

Motorola came to win at CES this year, and their smartphone offering is, in a word, awesome!  The phone itself is beefy (the dual-core Tegra 2 chip and 1GB of ram make playing 1080p video and Flash a breeze), but the coolest thing about it is the dock — which turns it into a laptop.

The phone just plugs into the back of the 2.4 pound laptop dock! You get an 11.6 inch screen with a compressed keyboard, a track pad, and web top software that lets you surf the full-sized web, even picking up where you left off on the phone. You can also access the phone’s interface, and run its apps in full screen. According to LaptopMag, you can even run Citrix Receiver, which allows you to basically run full Windows right there on the machine.
Very cool
publish by MIRZA AHSAN BAIG

Apple Enchancing photo features in ios5.............

Given the iPhone's popularity as a camera, it's no surprise that Apple would  look to boost the photography features contained in its mobile OS. But what's new in the Camera and Photo apps with iOS 5?

Insant excess

Imagine a moment is in front of you , by the time you take out mobile and open the camera application to catch the moment, the scene is gone by. To enhance camera availability , apple launches easy to access camera application. Now if you double-press the Home button, a camera icon appears to the right of the unlock slider. Tap it once, and the Camera app will automatically open.

  

 Physical Shutter Button

Apple has now has introduce a physical button in ios5 for snapping the image.  Using the button should feel more natural to use than tapping the screen; it will also minimize camera shake.

 new camera application

-There’s a new Grid option that divides the screen into thirds. It will help you properly frame your shots. To toggle the Grid view on and off, tap the Options button in the Camera app.

-You’ve always been able to tap once on screen to set the focus and exposure point for an image. But if you move the phone, or if the view changes too much, the Camera app will recalibrate and pick a new focus and exposure point. If you’d like to force a certain focus and exposure setting and lock it in place no matter where you point the camera, just tap and hold until the blue box appears and pulsates. The words AE/AF Lock appear at the bottom of your screen.

-you can still tap on a small thumbnail image to view the photo you just took. But there’s now a more intuitive way to view previously taken pictures: just swipe with one finger from left to right. It’s as if the camera interface is the most recent photo on the Camera Roll, with all your photos right behind it. It’s a good move: Swiping back to check your recent shots feels a lot more natural than tapping the thumbnail and navigating through the Camera Roll interface.

-If you want to zoom in, just stick two fingers on screen and spread them apart. The Camera app will do exactly what you expect it to do: Zoom in. Just pinch with two fingers to zoom back out.

New to the Photos app

With iOS 5, Apple has at last brought a bit of photo editing to the Photos app. The Auto-Enhance button (which is represented by a magic wand) will instantly improve an image by tweaking settings like sharpness, levels, and contrast, and automatically reducing red-eye.

Also new to Photos is the ability to create and edit photo albums directly on your device; previously, you could edit albums by using a third-party app or by transferring everything back to your computer for editing there. When you add a photo to a new album in iOS 5, it also stays in the main Camera Roll folder.


pubish bt Mirza Ahsan Baig

"Mango" Arrives with a Wi-Fi Tethering Surprise

When Windows Phone 7 was first launched, it received tepid reviews. It was missing key features like the capability to copy and paste text, and many of the core functions of the device like Wi-Fi, Outlook messaging, and general OS performance were lacking.

"Mango" turns Windows Phone into a real smartphone contender.In March of this year, Microsoft rolled out the "NoDo" update. "NoDo" was sort of like Windows Phone 7 Service Pack 1. It essentially fixed what was broken and made Windows Phone 7 what it should have been when it was launched. But, even with "NoDo" the Windows Phone platform wasn't really ready to go head to head with iOS and Android.

Now "Mango" is here. "Mango" is a major update with more than 500 changes and updates to the Windows Phone system. That is why Microsoft is now calling it Windows Phone 7.5 instead of Windows Phone 7.

I have been playing with a pre-release beta version of "Mango" for my 30 Days With Windows Phone 7 series, so I have already had an opportunity to explore some of the new features. I have been very impressed.

Here is a brief rundown of some of the highlights in "Mango":

• Messaging Threads: Within a messaging exchange between you and another party, you can switch the messaging platform on the fly. You can start off instant messaging, switch to SMS texting, then jump over to Facebook messaging all within one message thread.
• Group Contacts: With "Mango" you can create groups of contacts like "Family", or "Softball Team". You can filter incoming messages in the People Hub using the groups, and you can use the Group as a contact for outbound messages if you want to send an email or text message to the whole group.
• Local Scout: The Maps app in "Mango" has a new tool called Local Scout that identifies places nearby to eat or drink, tourist sites and things to do, and places to shop. You can also use it to plan a trip by finding where you're going to travel on the Maps app ahead of time and then using Local Scout to discover what's near there.
• Multitasking: "Mango" brings multitasking to Windows Phone 7 beyond the core functions of the OS. It's not "true multitasking", but it is precisely the right kind of multitasking for a smartphone OS.
• Speech Recognition: There is little you can't do just using voice commands with "Mango". The speech recognition functions allow you to place calls, open apps, search the Web, or get directions to a restaurant without touching the smartphone. You can also speak text messages, and have incoming messages read out loud so you can text while driving without touching the phone or taking your eyes off the road.
• Visual Search: "Mango" can do neat things like scan Microsoft Tags and QR codes, automatically identify and find information on books, CDs, and DVDs just by "looking" at the cover, and translate text to and from just about any language.

This list just scratches the surface of the 500 changes and updates in "Mango". Microsoft also surprised us all with a few bonus features that it had been holding up its sleeve. Microsoft launched a Web Marketplace for apps, and added Wi-Fi tethering capabilities.

The ability to piggyback on the 3G (or 4G) wireless connection to get other devices online can come in handy on occasion. Whether or not the tethering is allowed, or what it will cost will vary with your wireless provider, though, and there are some reports that the Wi-Fi implementation in "Mango" may have some other limitations to consider.

If you have a Windows Phone 7 device, you will love the "Mango" update. If you looked at Windows Phone 7 before and didn't like it, you owe it to yourself to look again next time you're in the market for a new smartphone. If you have never looked at Windows Phone 7, go check it out.

It's not perfect, but with "Mango" Microsoft might actually have a mobile OS that can contend head to head with iOS and Android.

posy by: Mirza Hassan Baig

source:http://www.pcworld.com/businesscenter/article/240735/mango_arrives_with_a_wifi_tethering_surprise.html

Seagate GoFlex Satellite: A Wireless Hard-Drive Tablet Companion

The Seagate GoFlex Satellite hard drive takes the shackles off your tablet, freeing it to connect to a greater amount of storage capacity--without having to go through any pesky wires. But although the hardware implementation is adequate, the software app struggles. A lot. At launch, Seagate is offering a messy, limited app for iPad and iPhone; an Android app equivalent is still in the works, so for now Android users must access the hard drive's contents using a comparatively crude Web-browser interface (admittedly, one not unlike the browser interface for standard network-attached drives).

The GoFlex Satellite ($200, price as of 5/20/2011) is slightly thicker and larger than most other portable hard drives, but not onerously so. In fact, it's about comparable in size to Seagate's own 1.5TB portable GoFlex, and to some of Iomega's 1TB eGo models (but not in price--you can get twice the capacity for half the price). Like the 1.5TB GoFlex, the GoFlex Satellite has a USB 3.0 USMadapter that plugs into the back of the drive; the use of USM opens the GoFlex Satellite up to a potential world of modular peripheral adapters, but it also adds about a half-inch to the depth.

Inside the chassis you get a 500GB hard drive with a battery rated for up to 5 hours of continuous streaming (assuming a single stream), or up to 25 hours of standby use. The device also offers integrated 802.11 b/g/n wireless (Wi-Fi being the secret to allowing a tablet with no ports to connect to the hard drive). On the outside are four functional additions: a DC input for the cleverly designed power cable, a power button to turn the Wi-Fi connectivity on and off, and two status lights on the top that show whether the wireless is on as well as the state of the battery's charge.

Seagate has ruggedized the drive's mounting inside its chassis, and improved its ability to withstand being transported helter-skelter. Seagate says, for example, that the drive was designed to endure being tossed into a backpack, and then being accessed from there--even while you're on the move.

Included in the box is a DC-input-to-USB 2.0 power cable. You can use this power cord to get juice through an extra USB port, via the 1.25-inch-square USB-to-wall-power adapter, or through the tiny USB-to-AC car adapter. It's a versatile design on the whole. My sole physical design gripe: The back cover that you can use to shield the USM adapter (if you prefer to pull off the USB connector) is difficult to remove.

In PCWorld Labs performance tests, the GoFlex Satellite earned a score of Good. It performed comparably to the Seagate GoFlex Pro, but other drives were incrementally faster on our tests.

App Design: Critical Stumble

Primarily, I tested the drive in conjunction with Seagate's GoFlex Media app on the Apple iPad 2. You can also use the drive via a Web browser--on Android tablets and phones, and even on iOS or Windows--but the experience is rougher there.

On the iPad, the iOS app starts off well with a pleasing two-pane interface that shows file-access shortcuts at the left and a viewer/access pane at the right. (On the iPhone, this structure is reduced to a one-pane-at-a-time approach, as necessitated by the phone's smaller screen.) On the left are sections for Videos, Photos, Music, Documents, and Folder View; tap there, and content of the appropriate file types then becomes visible in the main pane.

That good start is about as far as the app gets, though. In every other way, this 1.0 version comes up quite short. The problems are probably not unsolvable: Seagate has already said that it will address some of the disappointing aspects in future versions, and mobile users are certainly used to frequent app updates. Unfortunately, at this time the app is very limited, which in turn diminishes the usefulness of the drive itself.

Getting started is simple enough: You install the GoFlex Media app onto the iPad, and tap to open it. You can save a step if you go to the Wi-Fi settings and select the GoFlex drive as your wireless network before you open the app; otherwise, the app gives you instructions the first time you open it, or it will alert you when the unit is disconnected and you need to go out of the app to adjust the settings. Regrettably, fixing those settings is not something you can do from within the app. Every time it disconnects--or, say, whenever you exit the app to go to another app that needs an Internet connection--you'll have to revisit the settings to toggle to the Internet connection, and then do so again to reset the Wi-Fi back to the GoFlex Satellite. How much of this hassle is due to a limitation of Apple's iOS and how much is attributable to a limitation of the app itself is unclear; either way, it makes for a frustrating experience.

The GoFlex Media app does nothing to your files, and it has no built-in viewers, as some apps do. That means Seagate totally relies on Apple's iOS for file handling, and you can view a file only if it's already supported within iOS.

Seagate says it has optimized the app to handle video playback, and I found that the app does take care of the task well--with some peculiarities. You have to preformat your videos, or select videos that you bought from iTunes. Oddly, my iTunes-purchased, protected content could play, but only through the Web browser. At least that way I had audio available through the iPad's built-in speaker. My iPhone 4 videos played just fine in the app, but I couldn't get audio via the speaker; when I played the same video via the Web-browser interface, audio played just fine. Streaming worked surprisingly well for both high-definition (720p) and standard-definition video; I tried live-action and animation, and both types played fairly smoothly, albeit not perfectly (I noticed minor pixelation and macroblocking in some scenes).

To me, the frustrations with GoFlex Media seem to be basic design and development issues that lead to poor app behavior. Another example: When you're in the individual folders, you must first press a button (whose purpose is unclear) to get little checkboxes overlaid atop your images or documents; from there, you can choose whether to select individual files, select all files, play all files (in the case of music, photos, and videos), or download a file locally. Why not just allow you direct access, eliminating that extra, initial button press?

The app was also slow to reconnect to the drive after disconnection, and it was slow to display new content; sometimes, it would spin and spin and spin while trying to represent content, and it would have stayed in that state had I not clicked into a specific category.

Many more examples of poor design involve the photo component, which clearly is restricted in function. Once you open a photo, you can't move among your other images with basic next and back swipes, nor can you zoom in to a photo or do anything with it (at least in Apple's Photo Roll, you can tap an image to copy it, choose to e-mail or print an image, or select it as your new wallpaper). Photo icons display in an image thumbnail, but the aspect ratio is mangled, resulting in squashed-looking images. You can initiate a slideshow by selecting images and choosing 'Play all', but the result is crude: You have no control over the slideshow settings or transitions.

Even the locally stored content feels lost and limited: For instance, if you drill into music you've downloaded to your device, all you can do is play the tracks individually--you can't view them in any way but by file name, and you have no way to create playlists or sort by artist or album.

The GoFlex Satellite works fine in Windows Explorer--it's recognized as just another USB 3.0 hard drive there, and it performs as you'd expect any USB 3.0 hard drive to perform. You can't use the drive wirelessly while connected to a PC via USB, though. Seagate also includes a handy Media Sync software app to help you move content over to the drive. The app, for both PC and Mac, identifies your attached drives (Seagate and otherwise), and provides the ability to perform several precanned syncs: Simple iPad Sync (to find files your iPad can play or view), Simple Sync (to sync media folders with the external drive), and custom sync (to manually select the folders and media types to synchronize).

After I picked the iPad Sync function, I could then either proceed with the sync or choose to edit the sync options. From there, I could choose to sync files for iPad, iPhone 4, other iOS devices, other Apple devices, or other digital devices; changing the setting altered the set of file types supported in the sync. I then could select if I wanted photos, music, videos, and documents. Finally, I could decide whether to sync automatically or to click the Sync Now button.

Sadly, the GoFlex Media app never found and transferred my purchased iTunes video content. (Well, it found two parts of a multipart series of videos, and nothing else.) Seagate had no explanation for this.

Ultimately, the Seagate GoFlex Satellite is the first of what I expect to be many wireless hard drives designed to help tablet users get and share content from their PCs to their slates. The idea is clever, but the implementation leaves much to be desired. For now, this gadget is best left to those people who need to transport lots of video to a tablet--and who aren't concerned about digging through arcane file names and contending with glitches and poor app design. I'll update this review once the Android app becomes available, and if I hear that Seagate has overhauled the iOS app. It's frankly a shame that the company chose to rush it out the door with limited functionality.

posted by: Mirza Hassan Baig

source: http://www.pcworld.com/article/228316/seagate_goflex_satellite_a_wireless_harddrive_tablet_companion.html

LASER's:A BRIEF INTRO

A laser is a device that emits light (electromagnetic radiation) through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation. The emitted laser light is notable for its high degree of spatial and temporal coherence, unattainable using other technologies.

Spatial coherence typically is expressed through the output being a narrow beam which is diffraction-limited, often a so-called "pencil beam." Laser beams can be focused to very tiny spots, achieving a very high irradiance. Or they can be launched into a beam of very low divergence in order to concentrate their power at a large distance.

Temporal (or longitudinal) coherence implies a polarized wave at a single frequency whose phase is correlated over a relatively large distance (the coherence length) along the beam.A beam produced by a thermal or other incoherent light source has an instantaneous amplitude and phase which vary randomly with respect to time and position, and thus a very short coherence length.

Most so-called "single wavelength" lasers actually produce radiation in several modes having slightly different frequencies (wavelengths), often not in a single polarization. And although temporal coherence implies monochromaticity, there are even lasers that emit a broad spectrum of light, or emit different wavelengths of light simultaneously. There are some lasers which are not single spatial mode and consequently their light beams diverge more than required by the diffraction limit. However all such devices are classified as "lasers" based on their method of producing that light: stimulated emission. Lasers are employed in applications where light of the required spatial or temporal coherence could not be produced using simpler technologies.

Terminology

The word laser started as an acronym for "light amplification by stimulated emission of radiation"; in modern usage "light" broadly denotes electromagnetic radiation of any frequency, not only visible light, hence infrared laser, ultraviolet laser, X-ray laser, and so on. Because the microwave predecessor of the laser, the maser, was developed first, devices of this sort operating at microwave and radio frequenciesare referred to as "masers" rather than "microwave lasers" or "radio lasers". In the early technical literature, especially at Bell Telephone Laboratories, the laser was called an optical maser; this term is now obsolete.

A laser which produces light by itself is technically an optical oscillator rather than an optical amplifier as suggested by the acronym. It has been humorously noted that the acronym LOSER, for "light oscillation by stimulated emission of radiation," would have been more correct.With the widespread use of the original acronym as a common noun, actual optical amplifiers have come to be referred to as "laser amplifiers", notwithstanding the apparent redundancy in that designation.

The back-formed verb to lase is frequently used in the field, meaning "to produce laser light," especially in reference to the gain medium of a laser; when a laser is operating it is said to be "lasing." Further use of the words laser and maser in an extended sense, not referring to laser technology or devices, can be seen in usages such as astrophysical maser and atom laser.

Types and operating principles

Gas lasers

Following the invention of the HeNe gas laser, many other gas discharges have been found to amplify light coherently. Gas lasers using many different gases have been built and used for many purposes. The helium-neon laser (HeNe) is able to operate at a number of different wavelengths, however the vast majority are engineered to lase at 633 nm; these relatively low cost but highly coherent lasers are extremely common in optical research and educational laboratories. Commercial carbon dioxide (CO₂) lasers can emit many hundreds of watts in a single spatial mode which can be concentrated into a tiny spot. This emission is in the thermal infrared at 10.6 µm; such lasers are regularly used in industry for cutting and welding. The efficiency of a CO₂ laser is unusually high: over 10%. Argon-ion lasers can operate at a number of lasing transitions between 351 and 528.7 nm. Depending on the optical design one or more of these transitions can be lasing simultaneously; the most commonly used lines are 458 nm, 488 nm and 514.5 nm. A nitrogentransverse electrical discharge in gas at atmospheric pressure (TEA) laser is an inexpensive gas laser, often home-built by hobbyists, which produces rather incoherent UV light at 337.1 nm. Metal ion lasers are gas lasers that generate deep ultraviolet wavelengths. Helium-silver (HeAg) 224 nm and neon-copper (NeCu) 248 nm are two examples. Like all low-pressure gas lasers, the gain media of these lasers have quite narrow oscillation linewidths, less than 3 GHz (0.5 picometers),^[ making them candidates for use influorescence suppressed Raman spectroscopy.

Chemical lasers

Chemical lasers are powered by a chemical reaction permitting a large amount of energy to be released quickly. Such very high power lasers are especially of interest to the military, however continuous wave chemical lasers at very high power levels, fed by streams of gasses, have been developed and have some industrial applications. As examples, in the Hydrogen fluoride laser (2700-2900 nm) and the Deuterium fluoride laser(3800 nm) the reaction is the combination of hydrogen or deuterium gas with combustion products of ethylene in nitrogen trifluoride

Solid-state lasers

Solid-state lasers use a crystalline or glass rod which is "doped" with ions that provide the required energy states. For example, the first working laser was a ruby laser, made from ruby (chromium-dopedcorundum). The population inversion is actually maintained in the "dopant", such as chromium or neodymium. These materials are pumped optically using a shorter wavelength than the lasing wavelength, often from a flashtube or from another laser.

It should be noted that "solid-state" in this sense refers to a crystal or glass, but this usage is distinct from the designation of "solid-state electronics" in referring to semiconductors. Semiconductor lasers (laser diodes) are pumped electrically and are thus not referred to as solid-state lasers. The class of solid-state lasers would, however, properly include fiber lasers in which dopants in the glass lase under optical pumping. But in practice these are simply referred to as "fiber lasers" with "solid-state" reserved for lasers using a solid rod of such a material.

These lasers are also commonly frequency doubled, tripled or quadrupled, in so-called "diode pumped solid state" or DPSS lasers. Under second, third, or fourth harmonic generation these produce 532 nm (green, visible), 355 nm and 266 nm (Ultraviolet|UV]]) beams. This is the technology behind the bright laser pointersparticularly at green (532 nm) and other short visible wavelengths.Neodymium is a common "dopant" in various solid-state laser crystals, including yttrium orthovanadate (Nd:YVO₄), yttrium lithium fluoride (Nd:YLF) and yttrium aluminium garnet (Nd:YAG). All these lasers can produce high powers in the infrared spectrum at 1064 nm. They are used for cutting, welding and marking of metals and other materials, and also in spectroscopy and for pumping dye lasers.

Ytterbium, holmium, thulium, and erbium are other common "dopants" in solid-state lasers. Ytterbium is used in crystals such as Yb:YAG, Yb:KGW, Yb:KYW, Yb:SYS, Yb:BOYS, Yb:CaF2, typically operating around 1020-1050 nm. They are potentially very efficient and high powered due to a small quantum defect. Extremely high powers in ultrashort pulses can be achieved with Yb:YAG. Holmium-doped YAG crystals emit at 2097 nm and form an efficient laser operating at infrared wavelengths strongly absorbed by water-bearing tissues. The Ho-YAG is usually operated in a pulsed mode, and passed through optical fiber surgical devices to resurface joints, remove rot from teeth, vaporize cancers, and pulverize kidney and gall stones.

Titanium-doped sapphire (Ti:sapphire) produces a highly tunable infrared laser, commonly used for spectroscopy. It is also notable for use as a mode-locked laser producing ultrashort pulses of extremely high peak power.

Thermal limitations in solid-state lasers arise from unconverted pump power that manifests itself as heat. This heat, when coupled with a high thermo-optic coefficient (dn/dT) can give rise to thermal lensing as well as reduced quantum efficiency. These types of issues can be overcome by another novel diode-pumped solid-state laser, the diode-pumped thin disk laser. The thermal limitations in this laser type are mitigated by using a laser medium geometry in which the thickness is much smaller than the diameter of the pump beam. This allows for a more even thermal gradient in the material. Thin disk lasers have been shown to produce up to kilowatt levels of power.

Safety

Even the first laser was recognized as being potentially dangerous. Theodore Maiman characterized the first laser as having a power of one "Gillette" as it could burn through one Gillette razor blade. Today, it is accepted that even low-power lasers with only a few milliwatts of output power can be hazardous to human eyesight, when the beam from such a laser hits the eye directly or after reflection from a shiny surface. At wavelengths which the cornea and the lens can focus well, the coherence and low divergence of laser light means that it can be focused by the eye into an extremely small spot on the retina, resulting in localized burning and permanent damage in seconds or even less time.

Lasers are usually labeled with a safety class number, which identifies how dangerous the laser is:

• Class I/1 is inherently safe, usually because the light is contained in an enclosure, for example in CD players.
• Class II/2 is safe during normal use; the blink reflex of the eye will prevent damage. Usually up to 1 mW power, for example laser pointers.
• Class IIIa/3R lasers are usually up to 5 mW and involve a small risk of eye damage within the time of the blink reflex. Staring into such a beam for several seconds is likely to cause damage to a spot on the retina.
• Class IIIb/3B can cause immediate eye damage upon exposure.
• Class IV/4 lasers can burn skin, and in some cases, even scattered light can cause eye and/or skin damage. Many industrial and scientific lasers are in this class.

The indicated powers are for visible-light, continuous-wave lasers. For pulsed lasers and invisible wavelengths, other power limits apply. People working with class 3B and class 4 lasers can protect their eyes with safety goggles which are designed to absorb light of a particular wavelength.

Certain infrared lasers with wavelengths beyond about 1.4 micrometres are often referred to as being "eye-safe". This is because the intrinsic molecular vibrations of water molecules very strongly absorb light in this part of the spectrum, and thus a laser beam at these wavelengths is attenuated so completely as it passes through the eye's cornea that no light remains to be focused by the lens onto the retina. The label "eye-safe" can be misleading, however, as it only applies to relatively low power continuous wave beams; any high power or Q-switched laser at these wavelengths can burn the cornea, causing severe eye damage.

http://en.wikipedia.org/wiki/Laser